AD Values Research Articles

Adsorption of Glyphosate on Variable‐Charge, Volcanic Ash–Derived Soils

Glyphosate (N-phosphonometylglycine) is widely used due to its broad spectrum of activity and nonselective mode of action. In Chile it is the most used herbicide, but its adsorption behavior in the abundant and widespread variable charge soils is not well understood. In this study, three volcanic ash-derived soils were selected, including Andisols (Nueva Braunau and Diguillin) and Ultisols (Collipulli), to evaluate the adsorption kinetics, equilibrium isotherms, and the effect of pH in glyphosate adsorption. The influence of glyphosate on soil phosphorus retention was also studied. Glyphosate was rapidly and strongly adsorbed on the selected soils, and adsorption isotherms were well described by the Freundlich relationship with strong nonlinearity (n(fads) < 0.5). The n(fads) values were consistently higher than n(fdes) values, suggesting strong hysteresis. Adsorption (K(ads)) increased strongly when pH decreased. The presence of glyphosate (3200 mug mL(-1)) changed the adsorption behavior of phosphate at its maximum adsorption capacity. Andisol soils without the addition of glyphosate had similar mean K(ads) values for Nueva Braunau (5.68) and Diguillin (7.38). Collipulli had a mean K(ads) value of 31.58. During the successive desorption steps, glyphosate at the highest level increased K(ads) values for phosphate in the Andisol soils but had little effect in the Ultisol soil. This different behavior was probably due to the irreversible occupation of some adsorption sites by glyphosate in the Ultisol soil attributed to the dominant Kaolinite mineral. Results from this study suggest that in the two types of volcanic soils, different mechanisms are involved in glyphosate and phosphate adsorption and that long-term use of glyphosate may impose different effects on the retention and availability of phosphorus. Volcanic ash-derived soils have a particular environmental behavior in relation to the retention of organic contaminants, representing an environmental substrate that may become highly polluted over time due to intensive agronomic uses.

New spectroscopic studies of the comet- tail (A2Πi → X2Σ+) system of the 12C18O+ molecule

Four bands (with v′ = 2–5 and common v″ = 0) of the comet-tail (A2Πi → X2Σ+) band system were recorded under high resolution by conventional, photographic spectroscopy and their modern analysis was carried out. The current investigations include a much greater region of the observed 12C18O+ molecule spectrum than before. In particular, the 5–0 band was recorded and studied for the first time. Thanks to the application of high resolution it was possible to record the complete set of 12 branches in all bands studied. The high precision of the measurements and the use of the commonly accepted theoretical model allowed us to obtain full spectroscopic characteristics of the analysed excited vibrational levels v′ = 2–5 of the upper A2Πi state. In particular, the values of AD, p and q molecular constants for v′ = 2, 3, 4 and all rotational parameters for v′ = 5 were extracted for the first time. Also, the first values of the numerous equilibrium constants, as well as RKR parameters, were calculated. Finally, Franck–Condon factors and r-centroids for the comet-tail bands were provided.

정수기용 입상활성탄소 필터의 흡착특성에 관한 고찰

Quality test for activated carbon(AC) filter used for drinking water purifier is now an obligatory test and the standard material for valid purifying amount in water purifier performance test has been changed from residual chlorine to chloroform according to the notice of Ministry of Environment in 2006. Therefore, this study aimed to compare the ingredients of AC filters by confirming chloroform removal rate of AC filter and conducting 4 adsorption tests (Iodine, methylene blue decolorization, phenol value, ADS value) for AC filters provided by manufacturers. With water pressure of <TEX>$1kgf/cm^2$</TEX>, 1,500 liters of prepared inflow went through to check chloroform removal rate. As a result, product with removal rate of below 60% from all products. On the other hand, 4 adsorption tests were conducted for filters in the market and filters from manufacturers. None of the products satisfied all 4 tests. In particular, they showed great shortage to the standard in phenol value and ADS value test. However, manufacturers' filter showed much better performance than filters in the market. Also, the result of valid purifying amount test for each of five products of appropriate product and inappropriate product based on filter quality test showed average 4,440 liters for appropriate product and average 2,620 liters for inappropriate product. According to the result, it is shown that the filter with good adsorption also had good chloroform removal efficiency and adsorption efficiency. Therefore, it is expected that customers can screen good quality product through obligatory conduct of filter quality test. However, it is considered that complementation in system is required for future inspection.

Adsorption and Corrosion Inhibition Effect of 1,1′-Thiocarbonyldiimidazole on Mild Steel in H 2SO 4 Solution and Synergistic Effect of Iodide Ion

The inhibition effect of 1,1′-thiocarbonyldiimidazole (TCDI) on the corrosion behaviors of mild steel (MS) in 0.5 mol·L −1 H 2SO 4 solution was studied with the help of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) techniques. The effect of immersion time on the inhibition effect of TCDI was also investigated over 72 h. For the long-term tests, hydrogen evolution with immersion time ( V H 2– t) was measured in addition to the three techniques already mentioned. The thermodynamic parameters, such as adsorption equilibrium constant ( K ads) and adsorption free energy (Δ G ads) values, were calculated and discussed. To clarify inhibition mechanism, the synergistic effect of iodide ion was also investigated. The potential of zero charge (PZC) of the MS was studied by electrochemical impedance spectroscopy method, and a mechanism of adsorption process was proposed. It was demonstrated that inhibition efficiency increased with the increase in TCDI concentration and synergistically increased in the presence of KI. The inhibition efficiency was discussed in terms of adsorption of inhibitor molecules on the metal surface and protective film formation.

Determination of the adsorption free energy for peptide-surface interactions by SPR spectroscopy.

To understand and predict protein adsorption behavior, we must first understand the fundamental interactions between the functional groups presented by the amino acid residues making up a protein and the functional groups presented by the surface. Limited quantitative information is available, however, on these types of submolecular interactions. The objective of this study was therefore to develop a reliable method to determine the standard state adsorption free energy (delta Go ads) of amino acid residue-surface interactions using surface plasma resonance (SPR) spectroscopy. Two problems are commonly encountered when using SPR for peptide adsorption studies: the need to account for "bulk-shift" effects and the influence of peptide-peptide interactions at the surface. Bulk-shift effects represent the contribution of the bulk solute concentration to the SPR response that occurs in addition to the response due to adsorption. Peptide-peptide interactions, which are assumed to be zero for Langmuir adsorption, can greatly skew the isotherm shape and result in erroneous calculated values of delta Go ads. To address these issues, we have developed a new approach for the determination of delta Go ads using SPR that is based on the chemical potential. In this article, we present the development of this new approach and its application for the calculation of delta Go ads for a set of peptide-surface systems where the peptide has a host-guest amino acid sequence of TGTG-X-GTGT (where G and T are glycine and threonine residues and X represents a variable residue) and the surface consists of alkanethiol self-assembled monolayers (SAMs) with methyl (CH 3) and hydroxyl (OH) functionality. This new approach enables bulk-shift effects to be directly determined from the raw SPR versus peptide concentration data plots and the influence of peptide-peptide interaction effects to be minimized, thus providing a very straightforward and accurate method for the determination of delta Go ads for peptide adsorption. Further studies are underway to characterize delta Go ads for a large library of peptide-SAM combinations.

Energy-level alignment in the adsorption of phosphonyl reagents on γ-Al 2O 3

Density functional theory is applied to the computation of the adsorption energy (Δ E ads) for a series of molecules on γ-Al 2O 3. Three different cluster models are used to represent the γ-Al 2O 3 surface. The molecules of interest all contain a phosphonyl (P O) functional group and adsorb via formation of a donor bond between the O atom and a threefold-coordinated tetrahedral Al [Al(T d)] surface site. The highest occupied molecular orbital (HOMO) of the free molecule is, in all cases, composed largely of non-bonding orbitals on the O atom of the P O group. The empty “dangling orbital” on the coordinatively-unsaturated Al(T d) site constitutes a surface state. A linear relationship is found between Δ E ads and the difference between the orbital energies of the molecular HOMO ( ε H) and the surface state ( ε S). Trends in Δ E ads for different molecules can then be understood in terms of variations in ε H. Likewise, differences in Δ E ads for various cluster models can be explained by considering the differences in the predicted ε S values. A further evaluation of the cluster models is presented by comparing results for the physisorption of H 2O or CO with those obtained from two-dimensionally-periodic slab models. When differences in ε H and ε S are accounted for, the various models and computational procedures are seen to yield essentially equivalent results for adsorption of the molecules considered. These results are thought to constitute a useful conceptual tool for rationalizing Δ E ads values for different molecules and cluster models.

Investigation of adsorption and inhibitive effect of 2-mercaptothiazoline on corrosion of mild steel in hydrochloric acid media

The inhibition effect of 2-mercaptothiazoline (2MT) on the corrosion behavior of mild steel (MS) in 0.5 M HCl solution was studied in both short and long immersion times (120 h) using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. For long-term tests, hydrogen gas evolution ( V H 2 − t ) and the change of the open circuit potential with immersion time ( E ocp − t) were also measured in addition to the former three techniques. The surface morphology of the MS after its exposure to 0.5 M HCl solution with and without 1.0 × 10 −2 M 2MT with the different immersion times was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal stability of the inhibitor film was investigated by thermogravimetric analysis (TGA). The value of activation energy ( E a) for the MS corrosion and the thermodynamic parameters such as adsorption equilibrium constant ( K ads), free energy of adsorption (Δ G ads), adsorption heat (Δ H ads) and adsorption entropy (Δ S ads) values were calculated and discussed. The potential of zero charge (PZC) of the MS in inhibited solution was studied by the EIS method, and a mechanism for the adsorption process was proposed. The results showed that 2MT performed excellent inhibiting effect for the corrosion of the MS. Finally, the high inhibition efficiency was discussed in terms of adsorption of inhibitor molecules and protective film formation on the metal surface. TGA results also indicated that the inhibitor film on the surface had a relatively good thermal stability.

An Approach for Assessment of Compaction Curves of Fine Grained Soils at Various Energies Using a One Point Test

Compaction curves of soils are essential for establishing practical and reliable criteria for an effective control of field compaction. This paper deals with the development of a practical method of assessing laboratory compaction curves of fine-grained soils. It is found that for a given fine-grained soil compacted at a particular compaction energy, the relationships between water content (w) and degree of saturation (S) are represented by power function, which are w=AdSBd and w=AwSBw for the dry and the wet sides of optimum, respectively (where Ad, Aw, Bd and Bw are constant). The Bd and Bw values and optimum degree of saturation (ODS) are mainly dependent upon soil type irrespective of compaction energy. The Ad and Aw values decrease with the logarithm of compaction energy and the decrease rates are practically the same for any compacted fine-grained soil. This leads to a simple and rational method to assess the compaction curve wherein the compaction energy varies over a wide range using a one point test (a single test). Assuming that fine-grained soils compacted under standard Proctor energy behave in agreement with Ohio's curves, the modified Ohio's curves for the other three compaction energy levels (296.3, 1346.6 and 2693.3 kJ/m3) are developed based on the proposed method. These curves can be used to assess the entire compaction curves at the required compaction energy based on a single set data of dry unit weight and water content.

The Synthesis of Imidazoline Derivative Compounds as Corrosion Inhibitor towards Carbon Steel in 1% NaCl Solution

Oleic imidazoline is one of the nitrogen containing heterocyclic compounds that has been widely used as commercial corrosion inhibitor, especially in minimizing the carbon dioxide induced corrosion process in oilfield mining. In this present work, some imidazoline derivative compounds have been synthesized utilizing both conventional and microwave assisted organic synthesis (MAOS) methods, in order to determine their corrosion inhibition properties on carbon steel surface. The MAOS method is more effective in synthesizing these compounds than the conventional method regarding to the higher chemical yields of products (91% to 94%) and the shorter reaction times (7 to 10 minutes). The characterization of corrosion inhibition activities of the synthesized products towards carbon steel in 1% NaCl solution was determined by the Tafel plot method. The corrosion inhibition activities of compound 1b ((Z)-2-(2-(heptadec- 8-enyl)-4,5-dihydroimidazol-1-yl)ethanamine), 2b ((Z)-2-(2-(heptadec-8-enyl)- 4,5-dihydroimidazol-1-yl)ethanol) and 3b (2-(2-heptadecyl-4,5-dihydroimidazol- 1-yl)ethanamine) at 8 ppm concentration in 1% NaCl solution are, respectively, 32.18%, 39.59% and 12.73%. The heptadec-8-enyl and hydroxyethyl substituents at C(2) and N(1) position of imidazoline ring, respectively, gave the most effective corrosion inhibition activity towards carbon steel compared to the presence of other substituents. The increase in concentrations of compound 1b, 2b and 3b in 1% NaCl solution tends to improve their corrosion inhibition activities. Based on the analysis of the free Gibbs adsorption energy (ΔG 0 ads) values of compound 1b, 2b and 3b (-32.97, -34.34 and -31.27 kJ/mol, respectively), these compounds have the potential to interact with carbon steel through semi-physiosorption or semi-chemisorption.

Adsorption and corrosion inhibitive properties of 2-amino-5-mercapto-1,3,4-thiadiazole on mild steel in hydrochloric acid media

In this study, adsorption of 2-amino-5-mercapto-1,3,4-thiadiazole (2A5MT) on mild steel (MS) surface in 0.5 M HCl solution and its corrosion inhibition effect was studied in both short and long immersion times (over 120 h). For this purpose, a series of techniques, such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), thermogravimetric analysis (TGA), surface photographs, hydrogen evolution ( V H 2 – t ) and change of open circuit potential with immersion time ( E ocp– t) were utilized. The values of activation energy for MS corrosion and the thermodynamic parameters, such as adsorption equilibrium constant ( K ads), free energy of adsorption (Δ G ads), adsorption heat (Δ H ads) and adsorption entropy (Δ S ads) values were calculated and discussed. The potential of zero charge ( E pzc) of MS in inhibited solution was studied both after short and long immersion times by EIS method, and a mechanism of adsorption process was proposed. Results showed that 2A5MT performed excellent inhibiting effect for the corrosion of MS in 0.5 HCl solution and inhibition efficiency is higher than 99% after 120 h at 1.0 × 10 −2 M. The high inhibition efficiency was discussed in terms of strongly adsorption of inhibitor molecules on the metal surface and forming a protective film. Surface photographs showed a good surface coverage on the metal surface. TGA results indicated that the surface inhibitor film has relatively good thermal stability.

A new formula for correction of total calcium level into ionized serum calcium values in very elderly hospitalized patients

Ionized calcium (Ca 2+) seems to be the best measure of active serum calcium but, in France, numerous laboratories do not have Ca 2+ analyzers so that numerous clinicians use Payne's formula to obtain adjusted calcium (Ca Ad) values. In frail very elderly patients with protein/energetic malnutrition and very low concentrations of albumin, “correction” with Payne's formula usually gives false hypercalcemic results, so that hypocalcemia may be seriously underdiagnosed. Two hundred and ninety-four patients of 80 years and older with serum albumin level <35 g/l were included in four French hospitals for elderly people. Biological measurements were standardized in order to determine Ca 2+ and total calcium (Ca T) in accordance with approved guidelines. Ca Ad was calculated with Payne's formula whereas the dependence of Ca 2+ with serum protein, albumin and Ca Ad was investigated by linear regression, the goodness-of-fit of each equation with the measure of Ca 2+ being studied. Taking into account serum protein and albumin levels, multiple linear regression gave the equation: Ca 2+ (mmol/l) = 0.188 − 0.00469 protein (g/l) + 0.0110 albumin (g/l) + 0.401Ca Ad with r 2 = 0.442. The relative difference between the measure and the value given by the equation did not depend upon the center, and the correlation between measured and computed values of Ca 2+ was better, for any group, with our formula than with Payne's formula. When Ca 2+ was expressed with Ca T instead of Ca Ad, albumin term was no longer significant and the new equation was: Ca 2+ (mmol/l) = 0.592 − 0.00449 protein (g/l) + 0.410 total calcium (mmol/l) with r 2 = 0.438. We propose an alternative to direct measurement of Ca 2+ with a simple formula usable in geriatric units, which are often deprived of high-performance equipment.

The adsorption, CMC determination and corrosion inhibition of some N-alkyl quaternary ammonium salts on carbon steel surface in 2 M H 2SO 4

Electrochemical measurements were performed to investigate the effectiveness of cationic surfactants of the N-alkyl quaternary ammonium salt type, i.e. myristyltrimethylammonium chloride (MTACl), cetyldimethylbenzylammonium chloride (CDBACl), and trioctylmethylammonium chloride (TOMACl), as corrosion inhibitors for type X4Cr13 ferritic stainless steel in 2 M H 2SO 4 solution. Potentiodynamic polarization measurements showed that these surfactants hinder both anodic and cathodic processes, i.e. act as mixed-type inhibitors. It was found that the adsorption of the N-alkyl ammonium ion in 2 M H 2SO 4 solution follows the Langmuir adsorption isotherm. Plots of log [ θ/(1 − θ)] versus log c inh yielded straight lines with a slope, which changed drastically at the critical micelle concentration (CMC) of the surfactants studied. Accordingly, the CMC could be accurately determined from these measurements. The calculated values of the free energy of adsorption Δ G ads are, in cases when the charge on the metal surface is negative with respect to the PZC, relatively high what is characteristically for the chemisorption. On the other hand, for positive metal surfaces it is assumed that SO 4 2− anions are adsorbed first, so the cationic species would be limited by the surface concentration of anions. Accordingly Δ G ads values were lower in this case and the adsorption is due to merely electrostatic attraction, which is characteristically of physisorption.

Markedly Enhanced Cytolysis byE1B-19kD-Deleted Oncolytic Adenovirus in Combination with Cisplatin

Oncolytic adenoviruses are currently being developed as novel antitumor therapeutics. To enhance their therapeutic potential, adenoviruses are being administered in combination with standard chemotherapy. Adenoviral vectors used in these clinical trials, however, can be destructive as they encode intact E1B 19-kDa protein, which can block the apoptotic pathway induced by a variety of chemotherapeutic agents. Previously, we have shown that oncolytic adenovirus Ad-DeltaE1B19/55, deleted for sequence encoding E1B 19-kDa and E1B 55-kDa proteins, exhibits marked enhancement in cytolytic and apoptotic activity [Kim, J., Cho, J.Y., Kim, J.H., Jung, K.C., and Yun, C.O. (2002). Cancer Gene Ther. 9, 725-736]. In the current study, we assess the therapeutic value of Ad- DeltaE1B55 and Ad-DeltaE1B19/55 in combination with cisplatin. A marked increase in cytotoxicity was observed for both Ad-DeltaE1B55 and Ad-DeltaE1B19/55 when combined with cisplatin. Relative to each other in all cell lines examined, the combination of the double-deleted adenovirus, Ad-DeltaE1B19/55, plus cisplatin exhibited a greater cell-killing effect than did the single-deleted adenovirus, Ad-DeltaE1B55, plus cisplatin. Propidium iodide staining and TUNEL analysis also revealed that the combination of cisplatin with Ad-DeltaE1B19/55 caused greater induction of apoptosis than that with Ad-DeltaE1B55. Similarly, in vivo, the combination of Ad-DeltaE1B55 or Ad-DeltaE1B19/55 with cisplatin also induced greater antitumor effect in a human cervical xenograft model. TUNEL staining showed that the apoptotic level was significantly higher in tumor tissue treated with Ad-DeltaE1B19/55 plus cisplatin than with any other treatment. In addition, viral presence was confirmed by immunohistological staining, with increased numbers of adenoviral particles detected in wider areas of tumors treated with Ad-DeltaE1B19/55 oncolytic adenovirus plus cisplatin. Taken together, these findings demonstrate that cisplatin in combination with E1B- 19kD-deleted oncolytic adenovirus may enhance therapeutic efficacy (via active induction of apoptosis), eliciting a greater efficacy profile than that with E1B-19kD-expressing oncolytic adenovirus.

Sorption of Chromium(VI) from Aqueous Solution by Cassava (Manihot sculenta Cranz.) Waste Biomass

The sorption of highly toxic Cr(VI) ions by cassava waste biomass was quantitatively investigated. The sorption was found to be influenced by several physico-chemical factors such as agitation speed, temperature, contact time, pH, and sorbent/sorbate ratio. The adsorption data at equilibrium were fitted to Freundlich and Langmuir isotherms. The monolayer sorption capacity was found to be 61.79 mg of Cr(VI) per gram of biomass. The kinetics of Cr(VI) adsorption to pure cassava-tuber-bark wastes were determined based on a pseudo-second-order-rate model using the batch-sorption technique at a temperature of 30 degrees. The kinetics data suggest that the adsorption process is exothermic, and that the rate-limiting step is physisorption. Negative DeltaG(ads) values indicate that the adsorption is spontaneous and exothermic in nature. Also, under optimal conditions (in agitated 1M H(2)SO(4) at 30 degrees), the cassava waste biomass appears to be recyclable.

Localization Effect on the Metal Biosorption Capability of Recombinant Mammalian and Fish Metallothioneins in Escherichia coli

In this study, we examined the expression of mammalian and fish metallothioneins (MTs) in Escherichia coli as a strategy to enhance metal biosorption efficiency of bacterial biosorbents for lead (Pb), copper (Cu), cadmium (Cd), and zinc (Zn). In addition, MT proteins were expressed in either the cytoplasmic or periplasmic compartment of host cells to explore the localization effect on metal biosorption. The results showed that MT expression led to a significant increase (5-210%) in overall biosorption efficiency (eta(ads)), especially for biosorption of Cd. The MT-driven improvement in metal biosorption relied more on the increase in the biosorption rates (r(2), a kinetic property) than on the equilibrium biosorption capacities (q(max), a thermodynamic property), despite a 10-45% and 30-80% increase in q(max) of Cd and Zn, respectively. Periplasmic expression of MTs appeared to be more effective in facilitating the metal-binding ability than the cytoplasmlic MT expression. Notably, disparity of the impacts on biosorption ability was observed for the origin of MT proteins, as human MT (MT1A) was the most effective biosorption stimulator compared to MTs originating from mouse (MT1) and fish (OmMT). Moreover, the overall biosorption efficiency (eta(ads)) of the MT-expressing recombinant biosorbents was found to be adsorbate-dependent: the eta(ads) values decreased in the order of Cd > Cu > Zn > Pb.

Electrochemical quartz crystal nanobalance and chronocoulometry studies of phenylalanine adsorption on Au

The interfacial adsorption behaviour of the amino acid, phenylalanine (Phe), was studied at a polycrystalline Au surface in 0.05 M KClO 4 using cyclic voltammetry, chronocoulometry (CC) and electrochemical quartz crystal nanobalance (EQCN) frequency measurements. The frequency was observed to decrease with increasing concentration of Phe, indicating that the frequency measurements were following analyte adsorption directly. Both CC and EQCN frequency measurements showed a two-stage adsorption process, consistent with the molecule being adsorbed in the horizontal position at negative potentials, but rearranged to the more upright position at potentials more positive to the potential of zero charge. From the slopes at the onset of each of these two regions in plots of change in mass from the EQCN frequency measurements versus the surface charge density from CC measurements, the calculated molar mass corresponded to that of Phe displacing adsorbed water molecules for EQCN measurements made with small bulk concentrations of Phe (i.e., <1 × 10 −4 mol L −1). The adsorption process from CC measurements for Phe, described using the Henry adsorption isotherm, gave Gibbs energies of adsorption (Δ G ADS) ranging from −18 to −35 kJ mol −1 over the potential range of −0.6 to 0.6 V. The observed decrease in frequency of the EQCN measurements with additions of aliquots of amino acid and the substantial Δ G ADS values suggests that Phe adsorbs onto the surface via chemisorption. Surface concentrations (1.2 × 10 −10 mol cm −2) were in excellent agreement between the EQCN and CC measurements for small bulk concentrations of Phe (4.0 × 10 −5 mol L −1), in very good agreement with previously published results at the Au(1 1 1) surface. Thus, for small bulk concentrations of analyte, these electrochemical techniques complement one another to enhance our knowledge of the behaviour of thin organic films at electrode surfaces.

Monte Carlo calculation of radiation dose in CT examinations using phantom and patient tomographic models

By using a voxel-based Monte Carlo simulation technique, we developed and validated a method to calculate radiation-absorbed dose in the computed tomography (CT) examinations from the images of phantoms and patients. The ionising radiation transport was simulated using the EGS4 code system. The geometry of the X-ray beam (focus-to-axis distance, field of view, collimation, and primary and beam-shaper filtration) and the X-ray spectral distribution (HiSpeed LX/i) were included in the simulation. Each axial CT image was reduced to a 256 x 256 matrix and stacked in a volume. The patient images were segmented before the simulation of radiation transport by using four categories of materials, such as air, lung, muscle and bone. To test the voxel-based method, the values of the radiation dose derived from a simulated CT exposure were calculated and compared with those obtained from the measurements performed within the dosimetry phantoms. To complete the scope of the work, series of CT scans of the trunk of an anthropomorphic phantom and patients were simulated to calculate the average dose in each 1-cm-wide transverse slice (ADS). The comparison between the simulated and measured dose data for the CT indices showed a difference of <5% in all the cases. The estimated mean values of ADS from the chest, abdomen and pelvis of the anthropomorphic phantom were approximately 1.7-2 times the weighted CT dose index (CTDI(w)) value, whereas the mean ADS values for these anatomical areas were 1.3-2 times the CTDI(w) of patients. The voxel-based simulation method provided a technique for estimating the individual patient doses in the CT examinations.

Frontal Surface Area Versus Drag Area in Predicting Level Cycling Time Trial Performance

In road cycling, performance time on level terrain is highly influenced by aerodynamic resistance (Ra). At a given velocity, drag area is the primary component of Ra. Drag area is influenced by the bicycle-rider system's frontal surface area (AP) and its drag coeffcient. Traditionally, level time trial performance has been predicted based upon the assessment of a riders' frontal surface area, which represents only one component of the bicycle-rider system's drag area. PURPOSE To compare how actual measures of the rider frontal surface area (AP), estimates of the rider frontal surface area (APest), and direct determinants of the aerodynamic resistance of the bicycle/rider system measured as the drag area (AD), predict level cycling time trial performance (LTT) in the field when normalized to the measured power output (P). METHODS Nineteen highly trained cyclists (Mean ± SD VO2 peak = 67.6 ± 6.4) performed an all out 22.1 km LTT in the aerodynamic position and bicycle of their choice. Power output (304 ± 26 W) measured with a rear hub power meter and finish time (1884 ± 106 sec) were determined from the LTT. Drag area (0.349 ± 0.059 m2) was determined by using rear hub power meters to measure the relationship between tractive resistance and velocity squared. Projected frontal area (AP) was determined directly via the digitized planimetry technique (0.338 ± 0.049 m2) or indirectly with various estimation techniques (APest) currently used in the literature (range: 0.306 ± 0.020 to 0.550 ± 0.028 m2). LTT power was normalized to all values of AD (P/AD), AP (P/AP) and APest (P/APest), then correlated to LTT finish time. RESULTS (mean ± SD): P/AD (r = −0.926) correlated significantly stronger than all other correlations with time, while P/AP (r = −0.746) was not significantly different from any of the P/APest (r = −0.517 to −0.725) correlations to time. CONCLUSIONS Measures of the AD of the bicycle-rider system, which can be accurately determined in the field with a cycle mounted power meter, is a better predictor of performance time compared to direct measures of the AP using digitized planimetry or estimates of AP.

Synthesis, Nicotinic Acetylcholine Receptor Binding, and Antinociceptive Properties of 3‘-Substituted Deschloroepibatidine Analogues. Novel Nicotinic Antagonists

A series of 3'-substituted deschloroepibatidine analogues (3a-g and 4) showed high affinity for alpha4beta2 binding and relatively weak affinity for alpha7 nAChRs. The 3'-ethynyl (3g) and 3'-fluoro (3a) analogues with K(i) values of 0.02 and 0.037 nM, respectively, were the most potent. Even though the alpha4beta2 binding affinity of several of the analogues were equal to that of epibatidine, all of the compounds were weak agonists in the antinociceptive, hypothermia, and spontaneous activity test in mice. In contrast, all of the compounds were functional antagonists of nicotine-induced antinociception. In general, compounds 3a-g and 4 were more potent in the tail-flick assay than the hot-plate test. For example, the 3'-fluoro analogue 3a and the N-methyl-3'-iodo analogue 4 showed AD(50) values of 0.07 and 0.04 microg/kg, respectively, in the tail flick test and only 35 and 0% inhibition at 20 and 10 microg/kg in the hot-plate assay, respectively. These results suggest that these compounds will be highly useful for identifying which specific receptor subtypes are involved in each of nicotine's pharmacological effects. The high affinity of the N-methyl-3'-iodo analogue 4 combined with its weak agonist and potent antagonist activity suggests that carbon-11 and iodine-123 analogues may be useful as PET and SPECT ligands, respectively, for studying nAChRs in vivo.

1,3-Diaxial steric effects and intramolecular hydrogen bonding in the conformational equilibria of new cis-1,3-disubstituted cyclohexanes using low temperature NMR spectra and theoretical calculations

The conformational equilibria of 3-X-cyclohexanol [X = F ( 1), Cl ( 2), Br ( 3), I ( 4), Me ( 5), NMe 2 ( 6) and MeO ( 7)] and of 3-X-methoxycyclohexane [X = F ( 8), Cl ( 9), Br ( 10), I ( 11), Me ( 12), NMe 2 ( 13) and MeO ( 14)] cis isomers were determined from low temperature NMR spectra and PCMODEL calculated coupling constants. The energy differences between aa and ee conformers were obtained from these data ( Δ G J av and Δ G PC av , respectively) and also by the additivity principle from data for the monosubstituted cyclohexanes (Δ G Ad). H-1 and H-3 hydrogen vicinal coupling constants and Δ G J av values showed that the diequatorial conformer is predominant in the conformational equilibrium of the compounds studied at low temperature. However, Δ G PC av data show that compounds 6 and 7 constitute an exception, since they are almost equally populated by ee and aa at room temperature, due to stabilization of their aa conformer by an intramolecular hydrogen bond. Δ G Ad values, obtained according to the additivity principle, show a better agreement for compounds 2 and 3, since the 1,3-diaxial steric effect is counterbalanced by the formation of an intramolecular hydrogen bond (IAHB). For the remaining compounds, Δ G Ad values underestimate the energy differences, since the 1,3-diaxial steric effect, between X and OH or OCH 3, is absent in the monosubstituted compounds used as references. Moreover, the Δ G PC av , calculated from the coupling constants, obtained through the PCMODEL program, are rather smaller than the Δ G J av values, since the program does not have parameters for the effect, observed in this report, of a substituent at γ position on coupling constants values for the hydrogen under consideration.