Unexpected consequences of block polydispersity on the self-assembly of ABA triblock copolymers.

Controlled/"living" polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M(w)/M(n) = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M(w)/M(n) = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 ≤ f(B) ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly.

Spin polarization measurement of homogeneously doped Fe(1-x)Co(x)Si nanowires by Andreev reflection spectroscopy.

We report a general method for determining the spin polarization from nanowire materials using Andreev reflection spectroscopy implemented with a Nb superconducting contact and common electron-beam lithography device fabrication techniques. This method was applied to magnetic semiconducting Fe(1-x)Co(x)Si alloy nanowires with x̅ = 0.23, and the average spin polarization extracted from 6 nanowire devices is 28 ± 7% with a highest observed value of 35%. Local-electrode atom probe tomography (APT) confirms the homogeneous distribution of Co atoms in the FeSi host lattice, and X-ray magnetic circular dichroism (XMCD) establishes that the elemental origin of magnetism in this strongly correlated electron system is due to Co atoms.

Psychometric Equivalence of the Computerized and Original Halstead Category Test Using a Matched Archival Sample.

Objective: Investigate the equivalence of several psychometric measures between the traditional Halstead Category Test (HCT-Original Version [OV]) and the computer-based Halstead Category Test (HCT-Computerized Version [CV]). Method: Data were from a diagnostically heterogeneous, archival sample of 211 adults administered either the HCT by computer (n = 105) or cabinet (n = 106) as part of a neuropsychological evaluation. Groups were matched on gender, race, education, Full Scale Intelligence Quotient, and Global Neuropsychological Deficit Score. Confirmatory factor analysis was used to examine structural equivalence. Score, variability, and reliability equivalency were also examined. Differential item and test functioning under a Rasch model were examined. Results: An identified factor structure from research of the HCT-OV fit the HCT-CV scores adequately: χ2(4) = 8.83, p = .07; root mean square error of approximation = 0.10 [0.00, 0.20]; standardized root mean residual = 0.03; comparative fit index = 0.99. Total scores and variability of subtest scores were not consistently equivalent between the two administration groups. Reliability estimates were, however, similar and adequate for clinical practice: 0.96 for HCT-OV and 0.97 for HCT-CV. About 17% of items showed possible differential item functioning, though just three of these items were statistically significant. Differential test functioning revealed expected total score differences of <1% between versions. Conclusion: The results of this study suggest that the HCT-CV functions similar to the HCT-OV with there being negligible differences in expected total scores between these versions. The HCT-CV demonstrated good psychometric properties, particularly reliability and construct validity consistent with previous literature. Further study is needed to generalize these findings and to further examine the equivalency of validity evidence between versions.

The relationship between the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and olfaction in patients referred for a dementia evaluation.

The current study examined the relationship between a standardized dementia battery (Repeatable Battery for the Assessment of Neuropsychological Status [RBANS]) and a test of olfactory discrimination (University of Pennsylvania Smell Identification Test [UPSIT]) in a heterogeneous sample of patients referred for a dementia assessment (N = 103). Significant moderate correlations were found between the UPSIT and each of the RBANS indexes, with the strongest correlation for Total Scale score, followed by the Delayed Memory Index and the Language Index. Significant moderate correlations were also found between the UPSIT and 11 of the 12 subtests of the RBANS. While the major RBANS indexes demonstrated significant correlations with education and the Wechsler Test of Adult Reading, a measure of premorbid IQ, the UPSIT did not. This suggests the UPSIT may be sensitive to decline in dementia and largely unaffected by premorbid cognitive functioning. As a result, the UPSIT may provide neuropsychologists with an efficient, cost-effective, and sensitive supplement to a standard dementia battery.

Factor analysis of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) in a large sample of patients suspected of dementia.

The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS; Randolph, 1998) is a popular neuropsychological assessment instrument with research supporting its clinical utility. However, the index structure of the RBANS was derived theoretically and was not based on factor analysis. The purpose of this study was to examine the factor structure in a large heterogeneous sample of patients referred for a dementia evaluation, using exploratory factor analysis. Results suggest a two-factor solution, the first factor defined predominantly as a memory factor and the second as predominantly a visuospatial factor. This study also sought to validate the obtained factors by examining their relationship with external neuropsychological variables. Correlations between the external variables provide further support for Factor 1 as a memory factor. Correlations with Factor 2 support its visuospatial features, although this factor may also be associated with other cognitive domains such as attention and general ability.

Dichotomous scoring of Trails B in patients referred for a dementia evaluation.

The Trail Making Test is a popular neuropsychological test and its interpretation has traditionally used time-based scores. This study examined an alternative approach to scoring that is simply based on the examinees' ability to complete the test. If an examinee is able to complete Trails B successfully, they are coded as "completers"; if not, they are coded as "noncompleters." To assess this approach to scoring Trails B, the performance of 97 diagnostically heterogeneous individuals referred for a dementia evaluation was examined. In this sample, 55 individuals successfully completed Trails B and 42 individuals were unable to complete it. Point-biserial correlations indicated a moderate-to-strong association (r(pb)=.73) between the Trails B completion variable and the Total Scale score of the Repeatable Battery for the Assessment of Neurological Status (RBANS), which was larger than the correlation between the Trails B time-based score and the RBANS Total Scale score (r(pb)=.60). As a screen for dementia status, Trails B completion showed a sensitivity of 69% and a specificity of 100% in this sample. These results suggest that dichotomous scoring of Trails B might provide a brief and clinically useful measure of dementia status.

Correlation between the Bicycle Drawing Task and neuropsychological variables in patients referred for a dementia evaluation.

The objective of this study was to examine the relationship between the Bicycle Drawing Task and a number of neuropsychological variables, including the Repeatable Battery for the Assessment of Neuropsychological Status, in a heterogeneous group of older adults referred for a dementia evaluation. The sample consisted of 91 participants with a mean age of 77.0 yr. (SD = 6.4). The correlations between scores on the Bicycle Drawing Task and the Repeatable Battery for the Assessment of Neuropsychological Status and supplemental cognitive measures were generally in the moderate range. The Bicycle Drawing Task was not significantly related to premorbid IQ or education. As a neuropsychological measure, the task is brief, easily explained, easily scored, and well-tolerated by patients. Results suggest the Bicycle Drawing Task may be a useful screening procedure for cognitive impairment that is not significantly related to education or premorbid ability.

Examination of Regression-based Discrepancy Scores for the RBANS in Detecting Cognitive Impairment from an Archival Sample.

OBJECTIVE: The purpose of this study was to evaluate the clinical utility of regression-based formulas for the RBANS indexes in screening for cognitive impairment. METHOD: A database of neuropsychological test results was created from archival records in a memory assessment clinic. The sample consisted of 83 individuals (37 males/46 females) with an average age of 70.1 (SD = 9.8) and 14.6 years of education (SD = 2.8). Diagnostic accuracy of regression-based predictions provided by Duff and Ramezani (2015) (Duff, K., & Ramezani, A. (2015). Regression-based normative formulae for the Repeatable Battery for the Assessment of Neuropsychological Status for older adults. Archives of Clinical Neuropsychology, 30, 600-604.) and from regression of WTAR standard score were examined via receiver operator characteristic curves. Preliminary generalizability investigation was completed using two additional datasets. RESULTS: The WTAR was found to mediate the relationship between education and all RBANS index scores. The WTAR standard score was also found to contribute uniquely and significantly to the prediction of RBANS performance. Results of diagnostic accuracy analyses showed similar discriminating accuracy for all scores. There was limited support for using the WTAR over demographic variables alone in the estimation of RBANS performance; however, the WTAR was found to be more predictive than education, indicating potential clinical utility to using the word-reading score over just years of attained education. CONCLUSIONS: Use of these derived Total Scale score variants is recommended for the screening of cognitive impairment, particularly in individuals with superior or poor educational quality. Further research is required to evaluate the utility of these variations in more diverse samples.

Higher manganese silicide nanowires of Nowotny chimney ladder phase.

We report the synthesis, structural identification, and electrical properties of the first one-dimensional (1-D) nanomaterials of a semiconducting higher manganese silicide (MnSi(2-x)) with widths down to 10 nm via chemical vapor deposition of the single-source precursor Mn(CO)(5)SiCl(3). The complex Nowotny chimney ladder structure of these homologous higher manganese silicides, also referred to as Mn(n)Si(2n-m), MnSi(1.75), or MnSi(1.8), contributes to the excellent thermoelectric performance of the bulk materials, which would be enhanced by phonon scattering due to 1-D nanoscale geometry. The morphology, structure, and composition of MnSi(2-x) nanowires and nanoribbons are examined using electron microscopy and X-ray spectroscopy. Elaborate select area electron diffraction analysis on single-crystal nanowires reveals the phase to be Mn(19)Si(33), one of a series of crystallographically distinct higher manganese silicides that have a Nowotny chimney ladder structure. Electrical transport study of single nanowires shows that they are degenerately doped with a low resistivity (17 mohms x cm) similar to the bulk.

The relationship between smell identification and neuropsychological domains: Results from a sample of community-dwelling adults suspected of dementia.

OBJECTIVE: This study aimed to test the theoretical relationships between smell identification and cognitive tasks based on existing neuroimaging and anatomical findings. METHOD: Utilizing data collected from a memory assessment clinic, theory-derived mediation and moderation models were tested. The sample used in this study consisted of 103 (39 male, 64 female) individuals referred for memory assessments. The sample's mean education was 12.4 years (SD = 3.2), and the mean age of the sample was 77.2 years (SD = 6.3). RESULTS: The University of Pennsylvania Smell Identification Test (UPSIT) was a significant, partial mediator of the relationship between the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) Immediate and Delayed Memory indexes. Olfactory identification did not mediate list learning and retrieval; however, olfactory identification was a significant partial mediator of the relationship between story encoding and later memory retrieval of the story. Olfactory identification also fully mediated the relationship between a visuospatial construction task and its reconstruction from memory after a short delay. The relationship between processing speed and the olfactory identification was significantly mediated by semantic memory. Finally, the UPSIT moderated the relationship between a measure of premorbid ability, the Wechsler Test of Adult Reading, and current global cognitive functioning. CONCLUSIONS: Our results support theoretical relationships between olfaction and neuropsychological domains. Additionally, our results suggest that the UPSIT may serve as a proxy for cerebral integrity and is likely related to the duration of neurodegeneration.

Metallic single-crystal CoSi nanowires via chemical vapor deposition of single-source precursor.

We report the synthesis, structural characterization, and electrical transport properties of free-standing single-crystal CoSi nanowires synthesized via a single-source precursor route. Nanowires with diameters of 10-150 nm and lengths of greater than 10 mum were synthesized through the chemical vapor deposition of Co(SiCl(3))(CO)(4) onto silicon substrates that were covered with 1-2 nm thick SiO(2). Transmission electron microscopy confirms the single-crystal structure of the cubic CoSi. X-ray absorption and emission spectroscopy confirm the chemical identity and show the expected metallic nature of CoSi, which is further verified by room-temperature and low-temperature electrical transport measurements of nanowire devices. The average resistivity of CoSi nanowires is found to be about 510 muOmega cm. Our general and rational nanowire synthesis approach will lead to a broad class of silicide nanowires, including those metallic materials that serve as high-quality building blocks for nanoelectronics and magnetic semiconducting Fe(1-x)Co(x)Si suitable for silicon-based spintronics.

Neuropsychological performance of a patient suspected of dementia taking lorazepam and retested 1 year later following titration.

The effects of medication on neuropsychological performance have yet to be fully investigated, particularly in older patients. As such, the present case study was undertaken to examine the specific impact of benzodiazepine use on neuropsychological performance by providing a comparison of the test-retest data of an 81-year-old patient taking lorazepam. A comprehensive neuropsychological evaluation was conducted: (a) during the initial referral, while the patient had been taking high doses of lorazepam for approximately 3 years; and (b) 6 months after complete titration, which was 1 year after the initial evaluation. Normative scores derived from the 2 trials were compared via calculation of Reliable Change Indexes. Neuropsychological performance during both evaluations was indicative of dementia, including similar degrees of impairment in delayed memory, verbal fluency, and olfaction. However, scores obtained during the second evaluation were somewhat higher, with significant improvements observed in immediate memory, visuospatial/construction abilities, language function, abstract concept formation, and set shifting. Results of the current case study suggest that several neuropsychological domains may be particularly sensitive to chronic benzodiazepine use. Although the overall diagnostic picture in the present study remained unaltered, clinicians should be cognizant of such medication effects and the potential for these neuropsychological alterations to obscure differential diagnosis.

Relationship Between the Mini-Mental State Examination and the Repeatable Battery for the Assessment of Neuropsychological Status in Patients Referred for a Dementia Evaluation.

The current study examined the relationship between the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Mini-Mental State Examination (MMSE) in a large, heterogeneous sample of patients referred for dementia assessment (N = 495; 37% males, 63% females; M age = 76.8 years, SD = 7.0). The MMSE showed a significant moderate correlation with the RBANS Total Scale score (r = .65). Moderate significant correlations were found between the MMSE and the RBANS indexes (r = .41 to .49). The MMSE demonstrated moderate correlations with RBANS factor scores of .63 for Factor 1 (memory/learning) and .58 for Factor 2 (visuospatial/attention). These correlations suggest that the MMSE is best considered a measure of global cognitive functioning with the strongest correlations between broader measures.

Five-year outcomes following psychiatric consultation to a tertiary care emergency room.

OBJECTIVE: The authors prospectively examined inpatient psychiatric hospitalization and mortality rates of psychiatric patients seen in the emergency room of a large Department of Veterans Affairs medical center. METHOD: Charts of 504 patients receiving evening psychiatric consultation during a 13-month period were assessed 5 years after the consultation to determine rates of psychiatric hospitalization and mortality. RESULTS: Patients with multiple psychiatric diagnoses, including comorbid addiction disorders, had significantly higher rates of psychiatric hospitalization 5 years after an emergency room visit. Comorbid psychiatric disorders increased the rate of inpatient psychiatric hospitalization across diagnoses. Seventy-eight patients died during the study period. CONCLUSIONS: These findings reveal relationships between diagnostic profiles and future psychiatric hospitalization and mortality rates. This information could focus psychiatric and medical interventions for high-risk patients.

Mesoporous carbon-vanadium oxide films by resol-assisted, triblock copolymer-templated cooperative self-assembly.

Unlike other crystalline metal oxides amenable to templating by the combined assemblies of soft and hard chemistries (CASH) method, vanadium oxide nanostructures templated by poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) triblock copolymers are not preserved upon high temperature calcination in argon. Triconstituent cooperative assembly of a phenolic resin oligomer (resol) and an OBO triblock in a VOCl3 precursor solution enhances the carbon yield and can prevent breakout crystallization of the vanadia during calcination. However, the calcination environment significantly influences the observed mesoporous morphology in these composite thin films. Use of an argon atmosphere in this processing protocol leads to nearly complete loss of carbon-vanadium oxide thin film mesostructure, due to carbothermal reduction of vanadium oxide. This reduction mechanism also explains why the CASH method is not more generally successful for the fabrication of ordered mesoporous vanadia. Carbonization under a nitrogen atmosphere at temperatures up to 800 °C instead enables formation of a block copolymer-templated mesoporous structure, which apparently stems from the formation of a minor fraction of a stabilizing vanadium oxynitride. Thus, judicious selection of the inert gas for template removal is critical for the synthesis of well-defined, mesoporous vanadia-carbon composite films. This resol-assisted assembly method may generally apply to the fabrication of other mesoporous materials, wherein inorganic framework crystallization is problematic due to kinetically competitive carbothermal reduction processes.

Polydispersity-Driven Block Copolymer Amphiphile Self-Assembly into Prolate-Spheroid Micelles.

The aqueous self-assembly behavior of polydisperse poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) macromolecular triblock amphiphiles is examined to discern the implications of continuous polydispersity in the hydrophobic block on the resulting aqueous micellar morphologies of otherwise monodisperse polymer surfactants. The chain length polydispersity and implicit composition polydispersity of these samples furnishes a distribution of preferred interfacial curvatures, resulting in dilute aqueous block copolymer dispersions exhibiting coexisting spherical and rod-like micelles with vesicles in a single sample with a O weight fraction, wO, of 0.18. At higher wO = 0.51-0.68, the peak in the interfacial curvature distribution shifts and we observe the formation of only American football-shaped micelles. We rationalize the formation of these anisotropically shaped aggregates based on the intrinsic distribution of preferred curvatures adopted by the polydisperse copolymer amphiphiles and on the relief of core block chain stretching by chain-length-dependent intramicellar segregation.

Microstructure of Copolymers Formed by the Reagentless, Mechanochemical Remodeling of Homopolymers via Pulsed Ultrasound.

The high shear forces generated during the pulsed ultrasound of dilute polymer solutions lead to large tensile forces that are focused near the center of the polymer chain, but quantitative experimental evidence regarding the force distribution is rare. Here, pulsed ultrasound of quantitatively geminal-dihalocyclopropanated (gDHC) polybutadiene provides insights into the distribution. Pulsed ultrasound leads to the mechanochemical ring-opening of the gDHC mechanophore to a 2,3-dihaloalkene. The alkene product is then degraded through ozonolysis to leave behind only those stretches of the polymer that have not experienced large enough forces to be activated. Microstructural and molecular weight analysis reveals that the activated and unactivated regions of the polymer are continuous, indicating a smooth and monotonic force distribution from the midchain peak toward the polymer ends. When coupled to chain scission, the net process constitutes the rapid, specific, and reagentless conversion of a single homopolymer into block copolymers. Despite their compositional polydispersity, the sonicated polymers assemble into ordered lamellar phases that are characterized by small-angle X-ray scattering.

Mechanistic investigation of the growth of Fe1-xCoxSi (0 ≤ x ≤ 1) and Fe5(Si1-yGey)3 (0 ≤ y ≤ 0.33) ternary alloy nanowires.

We present the chemical vapor deposition (CVD) reactions of the single source precursor Fe(SiCl(3))(2)(CO)(4) over Si, Ge, CoSi(2)/Si, and CoSi/Si substrates to explore the growth and doping processes of silicide nanowires (NWs). Careful investigation of the composition and morphology of the NW products and the intruded silicide films from which they nucleate revealed that the group IV elements (Si, Ge) in the NW products originate from both the precursor and the substrate, while the metal elements incorporated into the NWs (Fe, Co) originate from vapor phase precursor delivery. The use of a Ge growth substrate enabled the successful synthesis of Fe(5)Si(2)Ge NWs, the first report of a metal silicide-germanide alloy NW. Further, investigation of the pyrolysis of the CoSiCl(3)(CO)(4) precursor revealed independent delivery of Co and Si species during CVD reactions. This understanding enabled a new, more robust two-precursor synthetic route to Fe(1-x)Co(x)Si alloy NWs using Fe(SiCl(3))(2)(CO)(4) and CoCl(2).

Chemical synthesis and magnetotransport of magnetic semiconducting Fe1-xCoxSi alloy nanowires.

We report single-crystal nanowires of magnetic semiconducting Fe1-xCoxSi alloys synthesized using a two-component single source precursor approach. Extending our previous syntheses of FeSi and CoSi nanowires from Fe(SiCl3)2(CO)4 and Co(SiCl3)(CO)4 precursors, we found that a homogeneous solution formed upon mixing these two precursors due to melting point suppression. This liquid constitutes the single-source precursor suitable for delivery through chemical vapor deposition, which enables the chemical synthesis of Fe1-xCoxSi alloy nanowires on silicon substrates covered with a thin (1-2 nm) SiO2 layer. Using scanning and transmission electron microscopy and energy dispersive X-ray spectroscopy and mapping, we demonstrate two homogenously mixed alloy nanowire samples with very different Co substitution concentrations (x): 6+/-5%, the ferromagnetic semiconductor regime, and 44+/-5%, the helical magnetic regime. The magnetotransport properties of these alloy nanowires are pronouncedly different from that of the host structures FeSi and CoSi, as well as from one another, and consistent with the physical properties as expected for their corresponding compositions. These novel magnetic semiconducting silicide nanowires will be important building blocks for silicon-based spintronic nanodevices.

Spin-dependent tunneling transport into CrO2 nanorod devices with nonmagnetic contacts.

Single-crystal nanorods of half-metallic chromium dioxide (CrO2) were synthesized and structurally characterized. Spin-dependent electrical transport was investigated in individual CrO2 nanorod devices contacted with nonmagnetic metallic electrodes. Negative magnetoresistance (MR) was observed at low temperatures due to the spin-dependent direct tunneling through the contact barrier and the high spin polarization in the half-metallic nanorods. The magnitude of this negative magnetoresistance decreases with increasing bias voltage and temperature due to spin-independent inelastic hopping through the barrier, and a small positive magnetoresistance was found at room temperature. It is believed that the contact barrier and the surface state of the nanorods have great influence on the spin-dependent transport limiting the magnitude of MR effect in this first attempt at spin filter devices of CrO2 nanorods with nonmagnetic contacts.