Controlled dissolution for elemental analysis of sample layers by inductively coupled plasma-mass spectrometry: a feasibility study

Aqueous acid mixtures at room temperature are used to partially dissolve steel samples. The dissolved elements are washed off the surface, diluted, and then determined by inductively coupled plasma-mass spectrometry (ICP-MS) using a magnetic sector mass analyzer. The amount of material removed is measured from the amount of Fe dissolved and increases linearly with HNO(3) concentration in the etch acid. Analyte concentrations in the solid are determined from the signal ratio of analyte ion/Fe(+). The shape of a plot of mass of element removed vs. nitric acid concentration yields information about the efficiency of the removal process and the likely chemical form of the element in the sample. For elements like Mn, Al, and W in steel, these plots have the same linear shape as that for the major element (Fe), and the measured concentrations agree well with the certified values. For problem elements like Nb and Ta, the plots have two linear regions with different slopes, and measured concentrations are lower than the certified values. Laser ablation ICP-MS and scanning electron microscopy (SEM) measurements show these elements to be associated together in the solid in refractory grains that are not dissolved to the same extent as the Fe matrix. For steel, the amount of Fe dissolved corresponds to an average depth of at least 4 microm, or 20 000 atomic layers.     

N‐Type Conjugated Polymer‐Enabled Selective Dispersion of Semiconducting Carbon Nanotubes for Flexible CMOS‐Like Circuits

Sorting of semiconducting single‐walled carbon nanotubes (SWNTs) by conjugated polymers has attracted considerable attention recently because of its simplicity, high selectivity, and high yield. However, up to now, all the conjugated polymers used for SWNT sorting are electron‐donating (p‐type). Here, a high‐mobility electron‐accepting (n‐type) polymer poly([N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)) (P(NDI2OD‐T2)) is utilized for the sorting of high‐purity semiconducting SWNTs, as characterized by Raman spectroscopy, dielectric force spectroscopy and transistor measurements. In addition, the SWNTs sorted by P(NDI2OD‐T2) have larger diameters than poly(3‐dodecylthiophene) (P3DDT)‐sorted SWNTs. Molecular dynamics simulations in explicit toluene demonstrate distinct linear or helical wrapping geometry between P(NDI2OD‐T2) and different types of SWNTs, likely as a result of the strong interactions between the large aromatic core of the P(NDI2OD‐T2) backbone and the hexagon path of SWNTs. By using high‐mobility n‐type P(NDI2OD‐T2) as the sorting polymer, ambipolar SWNT transistors with better electron transport than that attained by P3DDT‐sorted SWNTs are achieved. As a result, flexible negated AND and negated OR logic circuits from the same set of ambipolar transistors are fabricated, without the need for doping. The use of n‐type polymers for sorting semiconducting SWNTs and achieving ambipolar SWNT transistor characteristics greatly simplifies the fabrication of flexible complementary metal‐oxide‐semiconductor‐like SWNT logic circuits.     

Microstructure,Intermetallic Growth,and Reliability of Rapidly Solidified Pb-Free Solder Joints Formed via Solder Ball Jetting

The majority of research on Pb-free solders has been done with reflow times sufficient to allow significant intermetallic growth at the liquid solder/pad interface. With the need for small, fine-pitched solder joints and to avoid damage to heat-sensitive read/write sensors, the hard disk drive industry predominantly uses solder jet bonding for electrical connections of the heads. This technique does not use flux and has solidification times on the order of a millisecond, four orders of magnitude smaller than that of conventional solder technology. Therefore, the intermetallic formation is highly nonequilibrium and is localized near the pad interface. Surface finish thicknesses and composition have a significant influence on intermetallic growth and composition of solder joints. The intermetallic microstructure, along with voids, can significantly impact joint reliability. In this paper, results of wettability and mechanical solder ball shear measurements on as-plated and aged samples are reported and correlated with microstructure and growth of intermetallic compounds (IMCs) at the solder/pad interface. A wide range of Au-Sn IMCs are found at the pad interface, and Au-embrittlement effects are not found until Au exceeds 7 wt.%.     

Correlational analysis of verbal interactions during the consultative interview and consultees' subsequent perceptions.

We examined the relation of consultants' and consultees' verbal behavior during the problem identification interview (PII) to consultees' perceptions. 20 teachers engaged with 1 of 2 consultants in 15-min PIIs about a classroom problem. Verbal interaction patterns of the consultant and the consultee during each PII were coded according to J. R. Bergan and M. L. Tombari's (1975) system. After the PII, teachers responded to a 35-item questionnaire assessing their perceptions of the interview. Correlational analyses showed that favorable ratings of the interview were related significantly to the numbers of consultees' inference statements, consultants' positive validation statements, and consultees' statements describing behavior followed by consultants' positive validation. Implications for consultants' behavior during the PII are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Model of cortical-basal ganglionic processing: encoding the serial order of sensory events

Several lines of evidence suggest that the prefrontal (PF) cortex and basal ganglia are important in cognitive aspects of serial order in behavior. We present a modular neural network model of these areas that encodes the serial order of events into spatial patterns of PF activity. The model is based on the topographically specific circuits linking the PF with the basal ganglia. Each module traces a pathway from the PF, through the basal ganglia and thalamus, and back to the PF. The complete model consists of an array of modules interacting through recurrent corticostriatal projections and collateral inhibition between striatal spiny units. The model's architecture positions spiny units for the classification of cortical contexts and events and provides bistable cortical-thalamic loops for sustaining a representation of these contextual events in working memory activations. The model was tested with a simulated version of a delayed-sequencing task. In single-unit studies, the task begins with the presentation of a sequence of target lights. After a short delay, the monkey must touch the targets in the order in which they were presented. When instantiated with randomly distributed corticostriatal weights, the model produces different patterns of PF activation in response to different target sequences. These patterns represent an unambiguous and spatially distributed encoding of the sequence. Parameter studies of these random networks were used to compare the computational consequences of collateral and feed-forward inhibition within the striatum. In addition, we studied the receptive fields of 20,640 model units and uncovered an interesting set of cue-, rank- and sequence-related responses that qualitatively resemble responses reported in single unit studies of the PF. The majority of units respond to more than one sequence of stimuli. A method for analyzing serial receptive fields is presented and utilized for comparing the model units to single-unit data.     

Spatial location of the space charge effect in individual ion clouds using monodisperse dried microparticulate injection with a twin quadrupole inductively coupled plasma mass spectrometer

Pulses of analyte and matrix ions from individual drops are measured simultaneously using a twin quadrupole inductively coupled plasma mass spectrometer (ICP-MS). The sample solution is introduced by monodisperse dried microparticulate injection (MDMI). At modest Pb concentrations (500 ppm), a shoulder on the leading edge of the Li(+) signal appears. At higher matrix concentrations (1000 to at least 1500 ppm), a dip in the leading edge of the Li(+) signal develops. These changes in the shapes of the Li(+) pulses are attributed to space charge effects in the extraction system and ion optics of the mass spectrometer. A qualitative depiction for this behavior is proposed, in which the Li(+) ions are deflected out of the preferred ion path and then refocused by the ion optics. Part of the Li(+) ion cloud is driven ahead of the Pb(+) cloud, and part is trapped behind the Pb(+) cloud. The result is a shoulder on the leading edge of the Li(+) signal. With the Pb matrix present, the shapes of the analyte ion pulses are sensitive to the voltages applied to the first two ion lenses, especially the extractor lens. This observation shows that the part of the matrix effect that occurs in the ion optics takes place mainly in the first two lenses.     

Biological implementation of the temporal difference algorithm for reinforcement learning: Theoretical comment on O'Reilly et al. (2007).

The ability to survive in the world depends critically on the brain's capacity to detect earlier and earlier predictors of reward or punishment. The dominant theoretical perspective for understanding this capacity has been the temporal difference (TD) algorithm for reinforcement learning. In this issue of Behavioral Neuroscience, R. C. O'Reilly, M. J. Frank, T. E. Hazy, and B. Watz (2007, see record 2007-02025-004)) propose a new model dubbed primary value and learned value (PVLV) that is simpler than TD, and they claimed that it is biologically more realistic. In this commentary, the author suggests some slight modifications of a previous biological implementation of TD instead of adopting the new PVLV algorithm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multivariate pattern matching of trace elements in solids by laser ablation inductively coupled plasma-mass spectrometry: source attribution and preliminary diagnosis of fractionation

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is used with two variations of principal components analysis (PCA) for objective, routine comparisons of forensic materials without time-consuming and destructive sample dissolution. The relative concentrations of trace elements in a solid sample are examined to provide a "fingerprint" composition that can be used for identification and source matching of the material. Residue samples are matched to bulk materials using PCA. Variation of laser focus and PCA are also used to diagnose the severity of elemental fractionation in two metal samples that are prone to fractionation, brass and steel. Such fractionation remains the most significant limitation for accurate quantitative analyses by LA-ICPMS.