Numerical study of coherence of optical feedback in semiconductor laser dynamics

The nonlinear dynamics of semiconductor laser with coherent, as compared to incoherent, delayed optical feedback systems have been discussed and contrasted in prior research literature. Here, we report simulations of how the dynamics change as the coherence of the optical feedback is systematically varied from being coherent to incoherent. An increasing rate of phase disturbance is used to vary the coherence. An edge emitting, 830nm, Fabry Perot semiconductor laser with a long external cavity is simulated. Following this study, consideration of prior and future experimental studies should include evaluation of where on the continuum of partial coherence the delayed optical feedback sits. Partial coherence is a parameter that will affect the dynamics

Numerical study of coherence of optical feedback in semiconductor laser dynamics

The nonlinear dynamics of semiconductor laser with coherent, as compared to incoherent, delayed optical feedback systems have been discussed and contrasted in prior research literature. Here, we report simulations of how the dynamics change as the coherence of the optical feedback is systematically varied from being coherent to incoherent. An increasing rate of phase disturbance is used to vary the coherence. An edge emitting, 830nm, Fabry Perot semiconductor laser with a long external cavity is simulated. Following this study, consideration of prior and future experimental studies should include evaluation of where on the continuum of partial coherence the delayed optical feedback sits. Partial coherence is a parameter that will affect the dynamics

Anatomical Correlates of Age-Related Working Memory Declines

Aging studies consistently show a relationship between decreased gray matter volume and decreased performance on working memory tasks. Few aging studies have investigated white matter changes in relation to functional brain changes during working memory tasks. Twenty-five younger and 25 older adults underwent anatomical magnetic resonance imaging (MRI) scans to measure gray matter volume, diffusion tensor imaging (DTI) to measure fractional anisotropy (FA) as a measure of white matter integrity, and functional magnetic resonance imaging (fMRI) while performing a working memory task. Significant increases in activation (fMRI) were seen in the left dorsal and ventral lateral prefrontal cortex with increased working memory load and with increased age (older showing greater bilateral activation). Partial correlational analyses revealed that even after controlling for age, frontal FA correlated significantly with fMRI activation during performance on the working memory task. These findings highlight the importance of white matter integrity in working memory performance associated with normal aging

The evolution of TEP1, an exceptionally polymorphic immunity gene in Anopheles gambiae

<p>Abstract</p> <p>Background</p> <p>Host-parasite coevolution can result in balancing selection, which maintains genetic variation in the susceptibility of hosts to parasites. It has been suggested that variation in a thioester-containing protein called <it>TEP1 </it>(AGAP010815) may alter the ability of <it>Anopheles </it>mosquitoes to transmit <it>Plasmodium </it>parasites, and high divergence between alleles of this gene suggests the possible action of long-term balancing selection. We studied whether <it>TEP1 </it>is a case of an ancient balanced polymorphism in an animal immune system.</p> <p>Results</p> <p>We found evidence that the high divergence between <it>TEP1 </it>alleles is the product of genetic exchange between <it>TEP1 </it>and other TEP loci, i.e. gene conversion. Additionally, some <it>TEP1 </it>alleles showed unexpectedly low variability.</p> <p>Conclusion</p> <p>The <it>TEP1 </it>gene appears to be a chimera produced from at least two other <it>TEP </it>loci, and the divergence between <it>TEP1 </it>alleles is probably not caused by long-term balancing selection, but is instead due to two independent gene conversion events from one of these other genes. Nevertheless, <it>TEP1 </it>still shows evidence of natural selection, in particular there appears to have been recent changes in the frequency of alleles that has diminished polymorphism within each allelic class. Although the selective force driving this dynamic was not identified, given that susceptibility to <it>Plasmodium </it>parasites is known to be associated with allelic variation in <it>TEP1</it>, these changes in allele frequencies could alter the vectoring capacity of populations.</p

An fMRI study of saccadic and smooth pursuit eye movement control

PURPOSE. To compare the cortical networks that underlie oculomotor function in patients with age-related macular degeneration (AMD) with those in normally sighted control subjects, using functional magnetic resonance imaging (fMRI). METHODS. Six patients with bilateral geographic retinal atrophy due to AMD (age range, 55-83 years) were recruited for the study. The visual acuities of the patients ranged from 20/76 (0.58 logMAR) to 20/360 (1.26 logMAR). An additional six younger (age range, 22-31 years) and six older (age range, 54 -78 years) normally sighted individuals were recruited as control subjects. fMRI data were acquired on a 3.0-Tesla, scanner while subjects performed visually guided saccade (VGS) and smooth-pursuit (SmP) tasks. RESULTS. Contrasts between VGS and fixation on a stationary target identified a network of activation that included the frontal eye fields (FEFs), supplementary eye fields (SMA/SEFs), prefrontal cortex (PFC), intraparietal sulci (IPS), and the areas of the visual cortex (MT/V5, V2/V3, and V1) in control subjects and patients. A similar network was identified for comparisons between SmP and periods of fixation. Marked variability was observed in the performance of both tasks across all patients. For both tasks, the patients generally showed increased PFC and IPS activation, with decreased activation in visual cortex compared with the control subjects. The patients showed significantly increased activation of the FEFs and SMA/SEFs in the SmP task, compared with the control subjects. CONCLUSIONS. These data suggest that performance of both eye movement tasks required greater involvement of the cortical regions generally implicated in attention and effort in patients with AMD. (Invest Ophthalmol Vis Sci. 2008;49:1728 -1735) DOI:10.1167/iovs.07-0372 T he most common visual impairment in persons older than 50 years is a progressive loss of central visual function as a result of AMD. 1,2 It has been estimated that one in three individuals more than 75 years of age and 1 in 30 individuals more than 52 years of age are affected by AMD. 3 Previous research in our laboratory with patients having juvenile or age-related macular degeneration has demonstrated that good central visual acuity is critically important in performing everyday activities, such as reading, writing personal correspondence, and recognizing faces and expressions, and that patients with macular degeneration are impaired in these areas. 4 -8 Commonly, patients who are affected by AMD show some adaptation to their compromised visual system. This adaptation is observed clinically by the use of preferred retinal locations (PRLs) and viewing eccentrically outside of diseased foveae. The use of PRLs is effortful and fatiguing to the patients. Furthermore, many patients use different PRLs depending on the nature of the task. 9,10 Although adaptive in nature, the use of PRLs does not result in normal oculomotor function. For example, the reading rates of patients with AMD using PRLs are substantially lower than those of normally sighted subjects. 11-14 A potential reason for reduced function in patients using PRLs is abnormal scanning of text, which would involve unsteady fixation, and inaccurate saccadic and pursuit eye movements. The primary goal of the present study was to examine the cortical networks that underlie saccadic and pursuit eye movements in patients affected by AMD who use PRLs. To do this, patients and normally sighted control subjects performed saccadic and pursuit eye movement tasks interspersed with periods of central fixation while functional magnetic imaging data were acquired. This study provides insight into the downstream cortical consequences of retinal disease

Team Teaching in an Early Childhood Interdisciplinary Program: A Decade of Lessons Learned

Preparing students in the early childhood field to work with children both with and without disabilities and to collaborate with different professionals is an important endeavor for colleges and universities. The purpose of this paper is to articulate a unique model of program collaboration between early childhood special education and early childhood regular education that demonstrates a cohesive preservice teacher education program across two departments within one university. This unique 10-year history of interdisciplinary collaboration and team teaching provides insights into many of the benefits and challenges of this type of program. This paper presents an historical overview of the development of this collaborative program and describes the logistics of operating an interdisciplinary program at the administrative level. Information collected from faculty and students illustrates the benefits and challenges of team teaching. Finally, strategies for developing a successful program are discussed

Mapping the dynamical regimes of a SESAM mode-locked VECSEL with long cavity using time series analysis

The different dynamical regions of an optically-pumped SESAM mode-locked, long-cavity VECSEL system with a fundamental pulse repetition frequency of ~200 MHz are investigated. The output power, captured as 250 μs long time series using a sampling rate of 200 GSa/s, for each operating condition of the system, is analyzed to determine the dynamical state. A wavelength range of 985-995 nm and optical pump powers of 10 W-16.3 W is studied. The system produces high quality fundamental passive mode-locking (FML) over an extensive part of the parameter space, but the different dynamical regions outside of FML are the primary focus of this study. We report five types of output: CW emission, FML, modelocking of a few modes, double pulsing, and, semi-stable 4th harmonic mode-locking. The high sampling rate of the oscilloscope, combined with the long duration of the time series analyzed, enables insight into how the structure and substructure of pulses vary systematically over thousands of round trips of the laser cavity. Higher average output power is obtained in regions characterized by semi-stable 4th harmonic mode-locking than observed for FML, raising whether such average powers might be achieved for FML. The observed dynamical transitions from fundamental mode-locking provide insights into instability challenges in developing a stable, widely tunable, low repetition rate, turn-key system; and to inform future modelling of the system

Common ticks of Oklahoma and tick-borne diseases

The Oklahoma Cooperative Extension Service periodically issues revisions to its publications. The most current edition is made available. For access to an earlier edition, if available for this title, please contact the Oklahoma State University Library Archives by email at [email protected] or by phone at 405-744-6311

Biological resurfacing in a canine model of hip osteoarthritis

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