http://idea.library.drexel.edu/handle/1860/829 Search the Channel search http://idea.library.drexel.edu/simple-search http://idea.library.drexel.edu/handle/1860/4080 Title: Optimum cavity length for high conversion efficiency quantum well diode lasers <br/> <br/>Authors: Rosen, Arye <br/> <br/>Abstract: The cavity length which maximizes the peak power conversion efficiency is determined for quantum well diode lasers. These calculations are based upon simple models of the diode injection laser's electrical and optical behaviors, including saturation in the quantum well gain current characteristic. Here the influences of the distributed optical cavity loss, electrical resistivity, and facet reflectivity on the optimum cavity length are described. Although a lower facet reflectivity results in increased threshold current, there are advantages to longer devices, as the peak conversion efficiency is not reduced. Since the optimum cavity length is greater for low reflectivity, the diode series resistance is smaller. Furthermore, when operating at the point where conversion efficiency is a maximum, the power output of the device with low facet reflectivity exceeds that of the device with higher facet reflectivity. Therein lies the principle advantage of reduced front-facet reflectivities in high power, high efficiency quantum well diode lasers. Good agreement results when these predictions are applied to a strained InGaAs/AlGaAs single quantum well laser (A = 0.93 f./m). http://idea.library.drexel.edu/handle/1860/3961 Title: Working Memory Monitoring of Air Traffic Controllers Using Functional Near Infrared Spectroscopy <br/> <br/>Authors: Ayaz, Hasan; Bunce, Scott; Willems, Ben; Hah, Sehchang; Shewokis, Patricia A.; Izzetoglu, Kurtulus; Onaral, Banu <br/> <br/>Abstract: Significant progress has been made over the last decade in understanding the physiological and neural bases of cognitive processes and behavior. The advent of new and improved brain imaging tools, that allow monitoring brain activity in ecologically valid environments, is expected to allow better identification of neurophysiological markers of human performance. Further, deployment of portable neuroimaging technologies to real time settings could help assess cognitive and motivational states of personnel assigned to perform critical tasks. Functional Near-Infrared Spectroscopy (fNIR) is an emerging optical brain imaging technology that relies on optical techniques to detect changes of hemodynamic responses within the prefrontal cortex in response to sensory, motor, or cognitive activation. Teaming with ongoing studies at the Federal Aviation Administration (FAA) William J. Hughes Technical Center’s Research, Development, and Human Factors Laboratory, fNIR has been used to monitor certified controllers as they manage realistic scenarios under typical and emergent conditions. As part of the study, 24 participants performed a standardized n-back task; which is a working memory assessment task with 4 conditions of controlled difficulty level. Repeated measures analysis of variance showed that average oxygenation changes at voxel that is close to AF7 in International 10-20 System, located within left inferior frontal gyrus in the dorsalateral prefrontal cortex, correlates with the task difficulty and increases monotonically with increasing task difficulty (F(3,69)= 4.37, p < 0.05). Post hoc analyses confirmed the differences in oxygenation changes as a function of task difficulty with 3-back is larger than the 0- and1-back tasks. These results are in agreement with recent meta-analysis of fMRI data of n-back studies. http://idea.library.drexel.edu/handle/1860/2741 Title: Atlas-based indexing of brain sections via 2-D to 3-D image registration <br/> <br/>Authors: Gefen, Smadar; Kiryati, Nahum; Nissanov, Jonathan <br/> <br/>Abstract: A 2-D to 3-D nonlinear intensity-based registration method is proposed in which the alignment of histological brain sections with a volumetric brain atlas is performed. First, sparsely cut brain sections were linearly matched with an oblique slice automatically extracted from the atlas. Second, a planar-to-curved surface alignment was employed in order to match each section with its corresponding image overlaid on a curved-surface within the atlas. For the latter, a PDE-based registration technique was developed that is driven by a local normalized-mutual-information similarity measure. We demonstrate the method and evaluate its performance with simulated and real data experiments. An atlasguided segmentation of mouse brains’ hippocampal complex, retrieved from the Mouse Brain Library (MBL) database, is demonstrated with the proposed algorithm. http://idea.library.drexel.edu/handle/1860/2716 Title: Flexural vibrations and resonance of piezoelectric cantilevers with a nonpiezoelectric extension <br/> <br/>Authors: Shen, Zuyan; Shih, Wan Y.; Shih, Wei-Heng <br/> <br/>Abstract: A piezoelectric cantilever (PEC) is a flexural transducer consisting of a piezoelectric layer [e.g., lead zirconate titanate (PZT)] bonded to a nonpiezoelectric layer (e.g., stainless steel). A PEC with a thin nonpiezoelectric extension has two distinctive sections, each with a different thickness, different axial density, and elastic-modulus profiles and has been increasingly used as an in-situ biosensor. It has the advantages of dipping only the nonpiezoelectric extension part in an aqueous solution without electrically insulating the piezoelectric section as well as serving as the bonding pad for receptor immobilization. In this study, we examined the effect of the thin nonpiezoelectric extension on the flexural resonance spectrum and resonance vibration waveforms of PEC; in particular, how the length ratio between the piezoelectric section and the nonpiezoelectric extension section affects the resonance frequencies and resonance peak intensities of PEC. Theoretical resonance frequencies and resonance vibration waveforms were obtained using an analytical transcendental equation we derived by solving the flexural wave equation. Both experimental and theoretical results showed that the two-section structure distorted the flexural vibration waveforms from those of PEC without an extension. As a result, the higher-mode resonance peaks of PEC with a nonpiezoelectric extension could be higher than the first resonance peak due to the two-section structure. With PEC that has a piezoelectric section of 0.25-mm thick PZT bonded to 0.07 mm thick stainless steel of various length l1 and a 0.07-mm thick nonpiezoelectric extension of length l2, we showed that the first-mode-to-second-mode resonance peak intensity ratio had a maximum of 5.6 at l1/l2 = 0.75 and the first-modeto- second-mode resonance frequency ratio a minimum of 2.2 at l1/l2 = 1.8. These findings will undoubtedly help optimize the design and performance of PEC. http://idea.library.drexel.edu/handle/1860/2697 Title: Interaction between rhythms in the human basal ganglia: application of bispectral analysis to local field potentials <br/> <br/>Authors: Marceglia, Sara; Bianchi, Anna Maria; Baselli, Giuseppe; Foffani, Guglielmo; Cogiamanian, Filippo; Modugno, Nicola; Mrakic-Sposta, Simona; Priori, Alberto; Cerutti, Sergio <br/> <br/>Abstract: The application of deep brain stimulation (DBS) for the treatment of Parkinson’s disease offered a direct “insight” into the human electrical activity in subcortical structures. The analysis of the oscillatory activity [local field potentials (LFPs)] disclosed the importance of rhythms and of interactions between rhythms in the human basal ganglia information processing. The aim of this study wasto investigate the existence of possible nonlinear interactions between LFP rhythms characterizing the output structure of the basal ganglia, the globus pallidus internus, by means of bispectral analysis. The results of this study disclosed that the rhythms expressed in the globus pallidus internus of the untreated parkinsonian patient are not independent and, in particular, the low-beta (13–20Hz)band generates harmonics that are included in the high-beta (20–35 Hz) band. Conversely, in the dystonic globus pallidus, as well as in the parkinsonian globus pallidus afterdopaminergic medication (i.e., in the more “normal” condition), the rhythms are substantially independent and characterized by a strong activity in the low-frequency band that generates a second harmonic (4–14 Hz), mostly included in the same band. The interactions between rhythms in the human globus pallidus are therefore different in different pathologies and in different patient’s states. The interpretation of these interactions is likely critical for fully understanding the role of LFP rhythms in the pathophysiology of human basal ganglia. http://idea.library.drexel.edu/handle/1860/2665 Title: Silicon as a millimeter-wave monolithically integrated substrate - A new look <br/> <br/>Authors: Rosen, Arye; Caulton, Martin; Stabile, Paul <br/> <br/>Abstract: An important goal of microwave research has now been attained with the development of the technologies needed to fabricate monolithic microwave (mm-wave) integrated circuits. Questions regarding the use of monolithic versus hybrid circuits are investigated. Attention is given to the pros and cons of materials considered for use as monolithic substrates at mm-wave frequencies, the properties of the microstrip, and the effects of shorter wavelengths as the wavelengths become comparable with the microstrip cross section. A novel technology is considered for the fabrication of mm-wave devices utilizing ion-implantation, laser annealing, and unique secondary-ion mass spectrometry diagnostics. http://idea.library.drexel.edu/handle/1860/2633 Title: Respiratory rhythm entrainment by somatic afferent stimulation <br/> <br/>Authors: Potts, Jeffrey T.; Rybak, Ilya A.; Paton, Julian F. R. <br/> <br/>Abstract: Respiratory and locomotor patterns are coupled during locomotion. The objectives of this study were to (1) demonstrate that respiratory rhythms are entrained by sensory input from somatic afferents, (2) establish whether the parabrachial nucleus mediates entrainment, (3) examine responses of single respiratory neurons in the ventral respiratory group (VRG) to somatic afferent stimulation, and (4) use a computational model of the pontomedullary respiratory network (Rybak et al., 2004a,b) to suggest neuronal mechanisms for entrainment. We used an in situ preparation in young rats that retained pontomedullary respiratory circuits and spinal pathways transmitting somatosensory input. We demonstrate that rhythmic stimulation of somatic afferents entrains respiratory rhythm on a 1:1 basis (1:1), increasing breathing frequency up to 1.4 –2.2 times greater than spontaneous frequency. Stable entrainment occurred only when stimuli were delivered during expiration. Reversible blockade of the lateral parabrachial nucleus eliminated entrainment. Somatic afferent stimulation produced significant increases in the firing rate of augmenting expiratory (E2) neurons but shortened the firing duration of postinspiratory (post-I) neurons.Acomputational model reproduced 1:1 entrainment and other experimental findings based on the assumption that the somatic afferents initiate early onset of inspiration via activation of medullary E2 neurons. The model also predicted that afferent stimulation evoked transient hyperpolarization of ramp-inspiratory (ramp-I) neurons. This was confirmed experimentally by intracellular recording from ramp-I neurons. Our experimental and modeling results demonstrate that an entrainment pathway from somatic afferents to the VRG via the lateral parabrachial nucleus causes resetting of respiratory rhythm through excitation of E2 and consequent inhibition of post-I neurons. http://idea.library.drexel.edu/handle/1860/2611 Title: Detecting cognitive activity related hemodynamic signal for brain computer interface using functional near infrared spectroscopy <br/> <br/>Authors: Ayaz, Hasan; Izzetoglu, Meltem; Bunce, Scott; Heiman-Patterson, Terry; Onaral, Banu <br/> <br/>Abstract: The ideal non-invasive brain computer interface (BCI) transforms signals originating from human brain into commands that can control devices and applications. Hence, BCI provides a way for brain output that does not involve neuromuscular system. This represents an advantage for those individuals suffering from neuromuscular impairments such as Amyotrophic Lateral Sclerosis (ALS) or various types of paralysis. In this study we propose to design a new noninvasive BCI that is based on optical means to measure brain activity by monitoring hemodynamic response. The proposed system uses functional near infrared (fNIR) spectroscopy to detect cognitive activity from prefrontal cortex elicited voluntarily by performing a mental task namely N-back test. Our findings indicate that fNIR signal correlates with cognitive tasks associated with working memory. These experimental outcomes compare favorably with previous functional magnetic resonance imaging (fMRI) and complement electroencephalogram (EEG) findings. Since fNIR can be implemented in the form of a wearable and minimally intrusive device, it also has the capacity to monitor brain activity under real life conditions in everyday environments leading the way to potential applications of fNIR in BCI development for communication and entertainment purposes. http://idea.library.drexel.edu/handle/1860/2603 Title: Signaling perturbations induced by invading H. pylori proteins in the host epithelial cells: a mathematical modeling approach <br/> <br/>Authors: Dampier, William; Tozeren, Aydin <br/> <br/>Abstract: Helicobacter pylori (H. pylori), a gram-negative bacterium, infects the stomach of approximately 50% of the world population. H. pylori infection is a risk factor for developing chronic gastric ulcers and gastric cancer. The bacteria produce two main cytotoxic proteins: Vacuolating cytotoxin A (VacA) and Cytotoxin-Associated gene A (CagA). When these proteins enter the host cell they interfere with the host MAP Kinase and Apoptosis signaling pathways leading to aberrant cell growth and premature apoptosis. The present study expanded existing quantitative models of the MAP Kinase and Apoptosis signaling pathways to take into account the protein interactions across species using the CellDesigner tool. The resulting network contained hundreds of differential equations in which the coefficients for the biochemical rate constants were estimated from previously published studies. The effect of VacA and CagA on the function of this network were simulated by increasing levels of bacterial load. Simulations showed that increasing bacterial load affected the MAP Kinase signaling in a dose dependant manner. The introduction of CagA decreased the activation time of mapK signaling and extended activation indefinitely despite normal cellular activity to deactivate the protein. Introduction of VacA produced a similar response in the apoptosis pathway. Bacterial load activated both pathways even in the absence of external stimulation. Time course of emergence of transcription factors associated with cell division and cell death predicted by our simulation showed close agreement with that determined from a publicly accesible microarray dataset of H. pylori infected stomach epithelium. The quantitative model presented in this study lays the foundation for investigating the affects of single nucleotide polymorphisms (SNPs) on the efficiency of drug treatment. http://idea.library.drexel.edu/handle/1860/2595 Title: Accelerated search for biomolecular network models to interpret high-throughput experimental data <br/> <br/>Authors: Datta, Suman; Sokhansanj, Bahrad A. <br/> <br/>Abstract: Background: The functions of human cells are carried out by biomolecular networks, which include proteins, genes, and regulatory sites within DNA that encode and control protein expression. Models of biomolecular network structure and dynamics can be inferred from highthroughput measurements of gene and protein expression. We build on our previously developed fuzzy logic method for bridging quantitative and qualitative biological data to address the challenges of noisy, low resolution high-throughput measurements, i.e., from gene expression microarrays. We employ an evolutionary search algorithm to accelerate the search for hypothetical fuzzy biomolecular network models consistent with a biological data set. We also develop a method to estimate the probability of a potential network model fitting a set of data by chance. The resulting metric provides an estimate of both model quality and dataset quality, identifying data that are too noisy to identify meaningful correlations between the measured variables. Results: Optimal parameters for the evolutionary search were identified based on artificial data, and the algorithm showed scalable and consistent performance for as many as 150 variables. The method was tested on previously published human cell cycle gene expression microarray data sets. The evolutionary search method was found to converge to the results of exhaustive search. The randomized evolutionary search was able to converge on a set of similar best-fitting network models on different training data sets after 30 generations running 30 models per generation. Consistent results were found regardless of which of the published data sets were used to train or verify the quantitative predictions of the best-fitting models for cell cycle gene dynamics. Conclusion: Our results demonstrate the capability of scalable evolutionary search for fuzzy network models to address the problem of inferring models based on complex, noisy biomolecular data sets. This approach yields multiple alternative models that are consistent with the data, yielding a constrained set of hypotheses that can be used to optimally design subsequent experiments.