Ultrafast electron and hole dynamics in germanium nanowires

We present the first ultrafast time-resolved optical measurements, to the best of our knowledge, on ensembles of germanium nanowires. Vertically aligned germanium nanowires with mean diameters of 18 and 30 nm are grown on (111) silicon substrates through chemical vapor deposition. We optically inject electron-hole pairs into the nanowires and exploit the indirect band structure of germanium to separately probe electron and hole dynamics with femtosecond time resolution. We find that the lifetime of both electrons and holes decreases with decreasing nanowire diameter, demonstrating that surface effects dominate carrier relaxation in semiconductor nanowires.     

Characterization of Lunar Dust for Toxicological Studies. I: Particle Size Distribution

The particle size distribution (PSD) of lunar dust, the <20?μm portion of the regolith, was determined as an initial step in the study of the possible toxicological effects it may have on the human respiratory and pulmonary systems. Utilizing scanning electron microscopy, PSDs were determined for Apollo 11 (10084) and 17 (70051) dust samples, as well as lunar dust simulant JSC-1Avf. The novel methodology employed is described in detail. All measured PSDs feature a log-normal distribution having a single mode in a range 100–300?nm for lunar dust samples, but the lunar simulant has a mode at ～ 600?nm.     

Effects of relationship maintenance on psychological distress and dyadic adjustment among couples coping with lung cancer.

Objective: Relationship maintenance strategies help to ensure the continuation of valued relationships by keeping them at a certain level of intimacy. This study evaluated how lung cancer patients' and spouses' efforts to maintain their relationships affected their psychological and marital adjustment over time. Design: Psychosocial questionnaires were administered within 1 month of lung cancer treatment initiation (baseline) and 3 and 6 months later to 158 lung cancer patients and their spouses. Main Outcome Measures: Study outcomes were global severity index scores on the Brief Symptom Inventory, and total scores on the Dyadic Adjustment Scale. Results: Multilevel modeling analyses using the Actor-Partner Interdependence Model showed that, regardless of gender or social role (i.e., patient or spouse), individuals who engaged in the strategies of positivity, networks, and shared tasks reported less distress at baseline than other participants. Over time, the effects of providing more assurances and experiencing a partner's increased reliance on social networks differed: patient distress was exacerbated, and spouse distress was alleviated. Couples where both partners engaged in more frequent maintenance behaviors reported greater dyadic adjustment at baseline and over time. Conclusion: For couples coping with lung cancer, the initial treatment period may be an important time that sets the tone for future spousal interactions. Engaging in relationship maintenance during this stressful time may help mold more resilient relationships and facilitate adjustment as the disease progresses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural bases of moderation of cortisol stress responses by psychosocial resources.

Psychosocial resources have been tied to lower psychological and biological responses to stress. The present research replicated this relationship and extended it by examining how differences in dispositional reactivity of certain neural structures may underlie this relationship. Two hypotheses were examined: (a) psychosocial resources are tied to decreased sensitivity to threat and/or (b) psychosocial resources are associated with enhanced prefrontal inhibition of threat responses during threat regulation. Results indicated that participants with greater psychosocial resources exhibited significantly less cortisol reactivity following a stress task, as predicted. Analyses using functional magnetic resonance imaging revealed that psychosocial resources were associated with greater right ventrolateral prefrontal cortex and less amygdala activity during a threat regulation task but were not associated with less amygdala activity during a threat sensitivity task. Mediational analyses suggest that the relation of psychosocial resources to low cortisol reactivity was mediated by lower amygdala activity during threat regulation. Results suggest that psychosocial resources are associated with lower cortisol responses to stress by means of enhanced inhibition of threat responses during threat regulation, rather than by decreased sensitivity to threat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extraction of nisin from a 2.5% commercial nisin product using methanol and ethanol solutions

Nisin is a class Ia bacteriocin used widely in the food industry to inhibit a number of gram-positive pathogens. Although this peptide exhibits activity against many gram-positive bacteria, its effectiveness can vary significantly depending upon the food application. Encapsulation is one method that has been investigated for improving the activity of nisin. Improvement of the encapsulation efficiency of nisin requires purification of the compound, which can be accomplished utilizing organic solvents. The objective of this study was to use methanol and ethanol solutions to extract and concentrate nisin from a commercial preparation containing 2.5% nisin. Commercial nisin was extracted with different concentrations of ethanol or methanol in sterile water for up to 8 h. Approximately 75% of the nisin activity was recovered with 10 or 50% ethanol compared with less than 1% recovery with an ethanol concentration higher than 90%. Extraction with 10 or 50% methanol was approximately as effective as that with lower concentrations of ethanol. However, yields were significantly greater for extraction with methanol at concentrations greater than 90%. The solubility of the nisin likely influenced the extraction profiles for the conditions used. Purification for an 8-h extraction using 10 and 50% ethanol was 1.36 and 1.93 times, respectively. Purification was less than 0.1 at higher ethanol concentrations due to poor extraction. For methanol treatments, purification factors were all 1.09 to 5.98, and they increased as methanol concentration increased. This method for extracting and purifying nisin from dairy proteins using organic solvents may provide an alternative means for preparing and concentrating nisin for encapsulation and other applications.     

Shall we dance? How a multicopper oxidase chooses its electron transfer partner

Multicopper oxidases (MCOs) are encoded in the genomes of Eukarya, Bacteria, and Archea. These proteins are unique in that they contain at least four Cu atom prosthetic groups organized into one each of the three spectral classifications of copper sites in biology: type 1 (T1), type 2 (T2), and binuclear type 3 (T3), where the T2 and T3 sites form a trinuclear Cu cluster. With these four redox-active copper sites, the multicopper oxidases catalyze the four-electron (4e(-)) reduction of dioxygen to 2H2O, an activity that they alone share with the terminal heme-containing oxidases. Most MCOs exhibit broad specificity towards organic reductants, while a relatively small number of family members exhibit equally robust activity towards metal ions like Fe(II), Cu(I), and Mn(II) and, thus, are considered metallo-oxidases. This Account analyzes the structure-activity features of multicopper oxidases that determine their relative substrate specificity. Since the substrate oxidation step involves an outer-sphere electron transfer from the reductant to the T1Cu site in the protein, the concepts of Marcus theory are applied to unravel the origin of the substrate specificity of the multicopper ferroxidases.     

In vivo imaging of hydrogen peroxide with chemiluminescent nanoparticles

The overproduction of hydrogen peroxide is implicated in the development of numerous diseases and there is currently great interest in developing contrast agents that can image hydrogen peroxide in vivo. In this report, we demonstrate that nanoparticles formulated from peroxalate esters and fluorescent dyes can image hydrogen peroxide in vivo with high specificity and sensitivity. The peroxalate nanoparticles image hydrogen peroxide by undergoing a three-component chemiluminescent reaction between hydrogen peroxide, peroxalate esters and fluorescent dyes. The peroxalate nanoparticles have several attractive properties for in vivo imaging, such as tunable wavelength emission (460-630 nm), nanomolar sensitivity for hydrogen peroxide and excellent specificity for hydrogen peroxide over other reactive oxygen species. The peroxalate nanoparticles were capable of imaging hydrogen peroxide in the peritoneal cavity of mice during a lipopolysaccharide-induced inflammatory response. We anticipate numerous applications of peroxalate nanoparticles for in vivo imaging of hydrogen peroxide, given their high specificity and sensitivity and deep-tissue-imaging capability.