Adsorption energetics of CO on supported Pd nanoparticles as a function of particle size by single crystal microcalorimetry.

The heat of adsorption and sticking probability of CO on well-defined Pd nanoparticles were measured as a function of particle size using single crystal adsorption microcalorimetry. Pd particles of different average sizes ranging from 120 to 4900 atoms per particle (or from 1.8 to 8 nm) and Pd(111) were used that were supported on a model in situ grown Fe(3)O(4)/Pt(111) oxide film. To precisely quantify the adsorption energies, the reflectivities of the investigated model surfaces were measured as a function of the thickness of the Fe(3)O(4) oxide layer and the amount of deposited Pd. A substantial decrease of the binding energy of CO was found with decreasing particle size. Initial heat of adsorption obtained on the virtually adsorbate-free surface was observed to be reduced by about 20-40 kJ mol(-1) on the smallest 1.8 nm sized Pd particles as compared to the larger Pd clusters and the extended Pd(111) single crystal surface. This effect is discussed in terms of the size-dependent properties of the Pd nanoparticles. The CO adsorption kinetics indicates a strong enhancement of the adsorbate flux onto the metal particles due to a capture zone effect, which involves trapping of adsorbates on the support and diffusion to metal clusters. The CO adsorption rate was found to be enhanced by a factor of ∼8 for the smallest 1.8 nm sized particles and by ∼1.4 for the particles of 7-8 nm size.

Surface products and coverage dependence of dissociative ethane adsorption on Pt{110}-(1 x 2).

The dissociation of ethane on Pt{110}-(1 x 2) has been studied using supersonic molecular beam and temperature-programmed reaction techniques. The study unequivocally shows that the stable dissociation product of ethane on Pt{110}-(1 x 2) at all coverages is CCH2 at 350-400 K and CCH at 440 K. Temperature-programmed-reaction (TPR) experiments indicate that the CCH2 species decomposes to CCH with a reaction-limited peak temperature of 430 K. Above 450 K, the CCH species becomes unstable and decomposes with a peak temperature of 540 K. By 600 K, ethane dehydrogenates completely to form a surface carbon layer. The sticking probability is initially 0.02 at 370 K and 0.03 at 600 K and follows a linear (1-2theta) dependence for coverages of up to theta = 0.4 ML, where theta is defined as the number of C2Hx units per (1 x 2) unit cell. However, a much weaker coverage dependence at 800 K suggests that the carbon agglomerates into high-density islands.

Measurement of the energetics of metal film growth on a semiconductor: Ag/Si(100)-(2 x 1).

The first direct calorimetric measurements of the energetics of metal film growth on a semiconductor surface are presented. The heat of adsorption of Ag on Si(100)-(2 x 1) at 300 K decreases from approximately 347 to 246 kJ/mol with coverage in the first monolayer (ML) due to overlap of substrate strain from nearby Ag islands. It then rises quickly toward the bulk sublimation enthalpy (285 kJ/mol) as 3D particles grow. A wetting layer grows to 1.0 ML, but is metastable above approximately 0.55 ML and dewets when kinetics permit. This may be common when adsorbate islands induce a large strain in the substrate surface nearby.

Prophylactic mastectomy and genetic testing: an update.

PURPOSE/OBJECTIVES: To examine and discuss the possible benefits and difficulties with recommending prophylactic mastectomy to BRCA1- and BRCA2-positive women. DATA SOURCES: Published research articles, professional review articles, textbooks. DATA SYNTHESIS: Women with BRCA1 and BRCA2 mutations face a much higher risk of developing breast cancer than the general population, with limited options available for prevention. Prophylactic mastectomy has been shown to have a survival advantage in young women who carry BRCA1 and BRCA2 mutations. Challenges exist, however, in the use of prophylactic mastectomy and genetic testing. CONCLUSIONS: Methods of preventing breast cancer in BRCA1- and BRCA2-positive women currently are limited to watch-and-wait surveillance, prophylactic mastectomy, and, perhaps, chemoprevention. Genetic testing and prophylactic mastectomy each present unique challenges while offering certain benefits as well. Recent studies have shown survival advantages to BRCA1- and BRCA2-positive women who undergo prophylactic mastectomy. IMPLICATIONS FOR NURSING PRACTICE: Nurses need to be aware of the complex issues surrounding testing for BRCA1 and BRCA2 mutations and prophylactic mastectomy to be able to provide current information to patients and assist in decision making.

Surface characterization of hydroxyapatite and related calcium phosphates by XPS and TOF-SIMS.

The surfaces of six biologically interesting calcium phosphate (CaP) phases (hydroxyapatite, dibasic calcium phosphate dihydrate, dibasic calcium phosphate, monobasic calcium phosphate, beta-tribasic calcium phosphate, octacalcium phosphate) have been examined by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The intensity of an O(1s) shake-up satellite correlates with the phosphate oxygen content. Together with the Ca/P and O/Ca XPS peak ratios, this feature helps provide identification of the CaP phase(s) present in the surface of unknown samples and establish their mole fractions, as proven with a bone sample. Contributions from carbonate impurities can be quantified using its C(1s) peak at 279.9 eV and subtracted from the O(1s) line shape to aid identification. Principal component analysis (PCA) has been applied successfully to analyze TOF-SIMS spectra of these six CaP phases. Multivariate analysis can help differentiate these CaP phases using the first two PCs, which are dominated by the relative intensities of only a few key ions: PO3-, O-, Ca+, CaOH+, PO2-, and OH-.

A new device for emergency percutaneous transtracheal ventilation in partial and complete airway obstruction.

Several methods of percutaneous transtracheal ventilation have been described for the immediate relief of upper airway obstruction when conventional methods fail. This study was conducted to determine whether a single percutaneously placed catheter introducer (Arrow Emergency Infusion Device [EID]) could provide access adequate for percutaneous transtracheal ventilation with standard ventilatory modalities in an obstructed airway. Ten mongrel dogs were anesthetized, intubated, and monitored (for pulse, blood pressure, ECG, and arterial blood gases). The endotracheal tube was occluded. When the dogs became hypoxic and hypercarbic, the Arrow EIDs were inserted transtracheally and the dogs were ventilated with either a Bear 1 Adult Ventilator or a Mapleson D system. Percutaneous transtracheal ventilation by the Arrow EID adequately ventilated dogs with controlled partial (95%) or complete airway obstruction from hypoxic and hypercarbic states. The ease of insertion, decreased associated complications, ability to ventilate with easily available devices, and use with complete airway obstruction make the EID an effective device for transtracheal ventilation.

Effect of amygdalectomy on habituation and CER in rats.

Amygdalectomized, Sham operates and unoperated rats received 20 habituation trials followed by CER training during which the habituation stimulus was made a CS for 10 CS-UCS pairings. Although no reliable differences in rate of magnitude of habituation as measured by suppression ratio magnitudes and ITI durations were apparent between any groups, these same measures indicated that substantial deficits in conditioned suppression were produced by bilateral amygdalectomy. In addition the lesion produced a reliable deficit in unconditioned suppression and a slight but reliable reduction in the number of ccs of water consumed in a 24 hour period. These results are more consistent with the hypothesis that amygdalectomy interferes with the arousal of fear than with the proposals that this lesion produces deficits in habituation or in response inhibition.