Optically excited states in positronium

Optical excitation are reported of the 1 3S-2 3P transition in positronium, and a second excitation from n=2 to higher n states. The experiment used light from two pulsed dye lasers. Changes in the positronium annihilation rate during and after the laser pulse were used to deduce the excited state populations. The n=2 level was found to be saturable and excitable to a substantial fraction of n=2 positronium to higher levels. Preliminary spectroscopic measurements were performed on n=14 and n=15 positronium

Validating an image-based fNIRS approach with fMRI and a working memory task

In the current study, we extend a previous methodological pipeline by adding a novel image reconstruction approach to move functional near-infrared (fNIRS) signals from channel-space on the surface of the head to voxel-space within the brain volume. We validate this methodology by comparing voxel-wise fNIRS results to functional magnetic resonance imaging (fMRI) results from a visual working memory (VWM) task using two approaches. In the first approach, significant voxel-wise correlations were observed between fNIRS and fMRI measures for all experimental conditions across brain regions in the fronto-parieto-temporal cortices. In the second approach, we conducted separate multi-factorial ANOVAs on fNIRS and fMRI measures and then examined the correspondence between main and interaction effects within common regions of interest. Both fMRI and fNIRS showed similar trends in activation within the VWM network when the number of items held in working memory increases. These results validate the image-based fNIRS approach

Two Essays on the Recommendation Behavior of Multi-line Salespeople

This dissertation consists of two essays in which we examine the recommendation behavior of multi-line salespeople. Multi-line salespeople are those who are able to choose among overlapping, competing manufacturers’ products to make a recommendation to their customers. In this dissertation, we seek to explain why and how multi-line salespeople may recommend particular products to their customers. In the first essay, we examine why salespeople may recommend a particular product. Manufacturers frequently face the challenge of motivating distributor salespeople to focus efforts on their products rather than on their competitors’. Thus, manufacturers often rely on outcome (e.g., rewards) and behavior (e.g., training) controls. We refer to these as external controls because they reflect mechanisms by which one firm directs another firm’s employees. External controls tend to raise concerns among salespeople about the appropriateness of being influenced by an outside firm, which can be alleviated by seeking cues about their managers’ external controls. The results of a three-source, multilevel study suggests that manufacturers can enhance the ability of salesperson external controls to drive focused effort (i.e., recommendations) by increasing similar sales manager external controls; however, increasing dissimilar controls may reduce the positive impact of salesperson external controls on their focused effort. In the second essay, we examine how salespeople may recommend a particular product. The process of how purchase decisions are made by customers is well-known in the literature (i.e., self decision-making); however, to date, there has not been a complementary understanding of how purchase decisions are made for customers (i.e., self-other decision-making). The results from a qualitative study involving 71 covert participant observation encounters with salespeople across 71 store locations of 3 retailers indicate a three-step recommendation process: goals, strategies, and recommendations. Drawing upon field observations and the decision-making literature, we show that salespeople emphasize different goals when recommending products than customers making decisions for themselves. We also complement prior research by expanding the scope of known decision-making strategies (self and self-other lexicographic) and surfacing a new decision-making strategy (product homogenization). Finally, we identify three recommendation types, and link the steps in the process model via a set of integrating propositions

Validating a new methodology for optical probe design and image registration in fNIRS studies

Functional near-infrared spectroscopy (fNIRS) is an imaging technique that relies on the principle of shining near-infrared light through tissue to detect changes in hemodynamic activation. An important methodological issue encountered is the creation of optimized probe geometry for fNIRS recordings. Here, across three experiments, we describe and validate a processing pipeline designed to create an optimized, yet scalable probe geometry based on selected regions of interest (ROIs) from the functional magnetic resonance imaging (fMRI) literature. In experiment 1, we created a probe geometry optimized to record changes in activation from target ROIs important for visual working memory. Positions of the sources and detectors of the probe geometry on an adult head were digitized using a motion sensor and projected onto a generic adult atlas and a segmented head obtained from the subject's MRI scan. In experiment 2, the same probe geometry was scaled down to fit a child's head and later digitized and projected onto the generic adult atlas and a segmented volume obtained from the child's MRI scan. Using visualization tools and by quantifying the amount of intersection between target ROIs and channels, we show that out of 21 ROIs, 17 and 19 ROIs intersected with fNIRS channels from the adult and child probe geometries, respectively. Further, both the adult atlas and adult subject-specific MRI approaches yielded similar results and can be used interchangeably. However, results suggest that segmented heads obtained from MRI scans be used for registering children's data. Finally, in experiment 3, we further validated our processing pipeline by creating a different probe geometry designed to record from target ROIs involved in language and motor processing

Automatic quality assessment in structural brain magnetic resonance imaging

MRI has evolved into an important diagnostic technique in medical imaging. However, reliability of the derived diagnosis can be degraded by artifacts, which challenge both radiologists and automatic computer-aided diagnosis. This work proposes a fully-automatic method for measuring image quality of three-dimensional (3D) structural MRI. Quality measures are derived by analyzing the air background of magnitude images and are capable of detecting image degradation from several sources, including bulk motion, residual magnetization from incomplete spoiling, blurring, and ghosting. The method has been validated on 749 3D T(1)-weighted 1.5T and 3T head scans acquired at 36 Alzheimer's Disease Neuroimaging Initiative (ADNI) study sites operating with various software and hardware combinations. Results are compared against qualitative grades assigned by the ADNI quality control center (taken as the reference standard). The derived quality indices are independent of the MRI system used and agree with the reference standard quality ratings with high sensitivity and specificity (>85%). The proposed procedures for quality assessment could be of great value for both research and routine clinical imaging. It could greatly improve workflow through its ability to rule out the need for a repeat scan while the patient is still in the magnet bore

Global and regional cortical thinning in first-episode psychosis patients: relationships with clinical and cognitive features

BackgroundThe thickness of the cortical mantle is a sensitive measure for identifying alterations in cortical structure. We aimed to explore whether first episode schizophrenia patients already show a significant cortical thinning and whether cortical thickness anomalies may significantly influence clinical and cognitive features.MethodWe investigated regional changes in cortical thickness in a large and heterogeneous sample of schizophrenia spectrum patients (n=142) at their first break of the illness and healthy controls (n=83). Magnetic resonance imaging brain scans (1.5 T) were obtained and images were analyzed by using BRAINS2. The contribution of sociodemographic, cognitive and clinical characterictics was investigated.ResultsPatients showed a significant total cortical thinning (F=17.55, d=−0.62, p0.53). No significant group × gender interactions were observed (all p’s>0.15). There were no significant associations between the clinical and pre-morbid variables and cortical thickness measurements (all r’s<0.12). A weak significant negative correlation between attention and total (r=−0.24, p=0.021) and parietal cortical thickness (r=−0.27, p=0.009) was found in patients (thicker cortex was associated with lower attention). Our data revealed a similar pattern of cortical thickness changes related to age in patients and controls.ConclusionsCortical thinning is independent of gender, age, age of onset and duration of the illness and does not seem to significantly influence clinical and functional symptomatology. These findings support a primary neuro-development disorder affecting the normal cerebral cortex development in schizophrenia

Multi site polyadenylation and transcriptional response to stress of a vacuolar type H(+)-ATPase subunit A gene in Arabidopsis thaliana

BACKGROUND: Vacuolar type H(+)-ATPases play a critical role in the maintenance of vacuolar homeostasis in plant cells. V-ATPases are also involved in plants' defense against environmental stress. This research examined the expression and regulation of the catalytic subunit of the vacuolar type H(+)-ATPase in Arabidopsis thaliana and the effect of environmental stress on multiple transcripts generated by this gene. RESULTS: Evidence suggests that subunit A of the vacuolar type H(+)-ATPase is encoded by a single gene in Arabidopsis thaliana. Genome blot analysis showed no indication of a second subunit A gene being present. The single gene identified was shown by whole RNA blot analysis to be transcribed in all organs of the plant. Subunit A was shown by sequencing the 3' end of multiple cDNA clones to exhibit multi site polyadenylation. Four different poly (A) tail attachment sites were revealed. Experiments were performed to determine the response of transcript levels for subunit A to environmental stress. A PCR based strategy was devised to amplify the four different transcripts from the subunit A gene. CONCLUSIONS: Amplification of cDNA generated from seedlings exposed to cold, salt stress, and etiolation showed that transcript levels for subunit A of the vacuolar type H(+)-ATPase in Arabidopsis were responsive to stress conditions. Cold and salt stress resulted in a 2–4 fold increase in all four subunit A transcripts evaluated. Etiolation resulted in a slight increase in transcript levels. All four transcripts appeared to behave identically with respect to stress conditions tested with no significant differential regulation

³¹P magnetization transfer magnetic resonance spectroscopy: assessing the activation induced change in cerebral ATP metabolic rates at 3 T

Purpose: In vivo ³¹P MRS magnetization transfer (MT) provides a direct measure of neuronal activity at the metabolic level. This work aims to use functional ³¹P MRS-MT to investigate the change in cerebral ATP metabolic rates in healthy adults upon repeated visual stimuli. Methods: A magnetization saturation transfer sequence with narrowband selective saturation of γ-ATP was developed for ³¹P MT experiments at 3 T. Results: Using progressive saturation of γ-ATP, the intrinsic T1 relaxation times of phosphocreatine (PCr) and inorganic phosphate (Pi) at 3 T were measured to be 5.1±0.8 s and 3.0±1.4 s, respectively. Using steady-state saturation of γ-ATP, a significant 24±14% and 11±7% increase in the forward creatine kinase (CK) pseudo-first-order reaction rate constant, k₁, was observed upon visual stimulation in the first and second cycles respectively of a paradigm consisting of 10min-rest followed by 10min-stimulation, with the measured baseline k₁ being 0.35±0.04 s⁻¹. No significant changes in forward ATP synthase (ATPase) reaction rate, PCr/γ- ATP, Pi/γ-ATP, and NAD(H)/γ-ATP ratios, or intracellular pH were detected upon stimulation. Conclusion: This work demonstrates the potential of studying cerebral bioenergetics using functional ³¹P MRS-MT to determine the change in the forward CK reaction rate at 3 T