Probing Albumin Adsorption onto Calcium Phosphates by XPS and ToF-SIMS

In this study the binding and assembly of bovine serum albumin (BSA) onto three different calcium phosphate phases (hydroxyapatite, dibasic calcium phosphate dihydrate, and β-tricalcium phosphate) was investigated using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS was used to record adsorption isotherms and to quantify the amount of BSA adsorbed onto the different CaP surfaces. On all three surfaces a monolayer of adsorbed BSA was formed. ToF-SIMS was then used to investigate how the structure of BSA changes upon surface binding. ToF-SIMS data from BSA films on the three CaP surfaces showed intensity differences of secondary ions originating from both hydrophobic and hydrophilic amino acids. For a more quantitative examination of structural changes, we developed a ratio comparing the sum of intensities of secondary ions from hydrophobic and hydrophilic residues. A small, but statistically significant, increase in the value of this ratio (7%) was observed between a BSA film on hydroxyapatite versus dibasic calcium phosphate dihydrate. From this ratio we can make some initial hypotheses about what specific changes in BSA structure relate to these differences observed in the ToF-SIMS data.     

Potential nitrate removal in a coastal freshwater sediment (Haringvliet Lake, The Netherlands) and response to salinization

Nitrogen transformations and their response to salinization were studied in bottom sediment of a coastal freshwater lake (Haringvliet Lake, The Netherlands). The lake was formed as the result of a river impoundment along the south-western coast of the Netherlands, and is currently targeted for restoration of estuarine conditions. Nitrate porewater profiles indicate complete removal of NO(3)(-) within the upper few millimeters of sediment. Rapid NO(3)(-) consumption is consistent with the high potential rates of nitrate reduction (up to 200 nmol N cm(-3) h(-1)) measured with flow-through reactors (FTRs) on intact sediment slices. Acetylene-block FTR experiments indicate that complete denitrification accounts for approximately half of the nitrate reducing activity. The remaining NO(3)(-) reduction is due to incomplete denitrification and alternative reaction pathways, most likely dissimilatory nitrate reduction to NH(4)(+) (DNRA). Results of FTR experiments further indicate that increasing bottom water salinity may lead to a transient release of NH(4)(+) and dissolved organic carbon from the sediment, and enhance the rates of nitrate reduction and nitrite production. Increased salinity may thus, at least temporarily, increase the efflux of NH(4)(+) from the sediment to the surface water. This work shows that salinity affects the relative importance of denitrification compared to alternative nitrate reduction pathways, limiting the ability of denitrification to remove bioavailable nitrogen from aquatic ecosystems.     

Development of a lightweight low-current 10 K 4 T magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. We previously reported the development of a lightweight (1 kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We now report our progress in developing a new 10 K magnet of similar size made with smaller diameter Nb₃Sn wire which will produce a 4 T central field with approximately 5 A.     

An accelerator based fusion-product source for development of inertial confinement fusion nuclear diagnostics

A fusion-product source, utilizing a 150 kV Cockraft-Walton linear accelerator, has been refurbished to provide a reliable nuclear diagnostic development tool to the national inertial confinement fusion (ICF) research program. The accelerator is capable of routinely generating DD reaction rates at approximately 10(7)/s when using a 150 kV, 150 microA deuterium (D) beam onto an erbium (Er) or titanium (Ti) target doped with D, and D(3)He reaction rates at approximately 5 x 10(5)/s when using a using a 120 kV, approximately 100 microA D beam onto a Er or Ti target doped with (3)He. The new accelerator is currently being used in a number of projects related to the national ICF program at the OMEGA Laser Fusion Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], which includes the wedge range filter charged-particle spectrometry program [F. H. Seguin et al., Rev. Sci Instrum. 75, 3520 (2004)] and the magnetic recoil neutron spectrometer [J. A. Frenje et al., Rev. Sci. Instrum. 72, 854 (2001)].     

Discharge of methylmercury-enriched hypolimnetic water from a stratified reservoir

A study conducted from July 1995 to June 1996 examining spatial and temporal distribution of mercury (Hg) at the Caballo Reservoir, New Mexico, revealed that the highest levels of methylmercury (MMHg) occurred in both the inlet and the Rio Grande upstream of the reservoir. As a result, a second study was designed to identify possible sources of the elevated levels of MMHg, and to determine if water discharged from the Elephant Butte Reservoir upstream could be a primary source. In July 1996, as anoxia began to develop in the hypolimnion of the Elephant Butte Reservoir, surface water MMHg concentrations were below the MDL of 0.018 ng/l while water discharged into the tailrace was 0.149 ng/l MMHg. By September 1996, when the anoxic hypolimnion spanned 60% of the total reservoir depth, surface water MMHg was still below the MDL, while discharge water had increased to 1.144 ng/l MMHg. Following reservoir turnover in November 1996, surface water increased to 0.264 ng/l MMHg while discharge water decreased to 0.420 ng/l MMHg. By January 1997, MMHg in the tailrace decreased to pre-stratification levels, and both surface water and discharge water reached similar MMHg levels until the onset of summer stratification in July 1997. This trend was repeated the following year when MMHg concentrations in the tailrace increased from 0.190 ng/l in August 1997 to 1.240 ng/l in September 1997. In addition, vertical profile sampling of the reservoir from August 1997 to September 1997 showed a buildup of MMHg in the anoxic hypolimnion which coincided with increasing levels of MMHg discharged into the tailrace. During the course of this study the single largest contribution of MMHg to the river below the reservoir was from water released through the dam during the fall months of the year.     

Parametric investigation of load-induced structure remodeling in the proximal femur

The process of adaptive bone remodeling can be simulated with a self-optimizing finite element method. The basic remodeling rules attempt to obtain a constant value for the strain energy per unit bone mass, by adapting density. The precise solution is dependent on the loads, initial conditions, and the parameters of the remodeling rule. While there are several investigations on developing algorithms leading to the bone density distribution in the proximal femur, these algorithms often require a large number of iterations. The aim of this study was to develop a more efficient adaptive bone remodeling algorithm, and to identify how the bone density distribution of the proximal femur was affected by parameters that govern the remodeling process. The forces at different phases of the gait cycle were applied as boundary conditions. The bone density distributions from these forces were averaged to estimate the density distribution in the proximal femur. The effect of varying the initial bone density, spatial influence function, non-linear order of the adaptive algorithm, and the influence range on the converged solution were investigated. The proposed procedure was shown to converge in a fewer number of iterations and requiring less computational time, while still generating a realistic bone density distribution. It was also shown that varying the identified parameters within reasonable upper and lower bounds had very little impact on the qualitative form of the converged solution. In contrast, the convergence rate was affected to a greater degree by variation of these parameters. In all cases, the solutions obtained are comparable with the actual density in the proximal femur, as measured by Dual-energy X-ray absorptiometry (DEXA) scans.     

Directional hyperattention in tactile neglect within grasping space

This study was motivated by the fact that unilateral neglect, an impediment to progress in patient rehabilitation, is often reported to occur in a wider area of space than that usually assessed in clinical settings. Neglect within "grasping space" (Halligan & Marshall, 1991; Kolb & Whishaw, 1990) was assessed via two search tasks: one in which search was guided by visual information and the other in which search was guided by tactile information. The performance of 10 left brain-damaged patients (LBD) and 20 right brain-damaged patients, 10 of whom showed left visual neglect (RBD+) while 10 did not (RBD-), was compared with that of age-matched controls. The visual search task confirmed the clinical diagnoses of unilateral visual neglect. On the tactile test, both RBD groups showed reduced search within the left hemispace, although this was a particularly strong feature of the performance of the RBD+ patients. Furthermore, this reduced leftwards exploration in RBD+ patients was associated with an increased frequency of repetitions made within the right hemispace, as had also been noted in some of these patients on conventional visual star cancellation. Results are discussed in relation to hyperattentional theories of directional spatial neglect.