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Search Results: 1 - 10 of 286720 matches for " K. E. Myers "
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Transcriptome-Wide Assessment of Human Brain and Lymphocyte Senescence
Mun-Gwan Hong, Amanda J. Myers, Patrik K. E. Magnusson, Jonathan A. Prince
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003024
Abstract: Background Identifying biological pathways that vary across the age spectrum can provide insight into fundamental mechanisms that impact disease and frailty in the elderly. Few methodological approaches offer the means to explore this question on as broad a scale as gene expression profiling. Here, we have evaluated mRNA expression profiles as a function of age in two populations; one consisting of 191 individuals with ages-at-death ranging from 65–100 years and with post-mortem brain mRNA measurements of 13,216 genes and a second with 1240 individuals ages 15–94 and lymphocyte mRNA estimates for 18,519 genes. Principal Findings Among negatively correlated transcripts, an enrichment of mitochondrial genes was evident in both populations, providing a replication of previous studies indicating this as a common signature of aging. Sample differences were prominent, the most significant being a decrease in expression of genes involved in translation in lymphocytes and an increase in genes involved in transcription in brain, suggesting that apart from energy metabolism other basic cell processes are affected by age but in a tissue-specific manner. In assessing genomic architecture, intron/exon sequence length ratios were larger among negatively regulated genes in both samples, suggesting that a decrease in the expression of non-compact genes may also be a general effect of aging. Variance in gene expression itself has been theorized to change with age due to accumulation of somatic mutations and/or increasingly heterogeneous environmental exposures, but we found no evidence for such a trend here. Significance Results affirm that deteriorating mitochondrial gene expression is a common theme in senescence, but also highlight novel pathways and features of gene architecture that may be important for understanding the molecular consequences of aging.
The Angular Clustering of Infrared-Selected Obscured and Unobscured Quasars
M. A. DiPompeo,A. D. Myers,R. C. Hickox,J. E. Geach,K. N. Hainline
Physics , 2014, DOI: 10.1093/mnras/stu1115
Abstract: Recent studies of luminous infrared-selected active galactic nuclei (AGN) suggest that the reddest, most obscured objects display a higher angular clustering amplitude, and thus reside in higher-mass dark matter halos. This is a direct contradiction to the prediction of the simplest unification-by-orientation models of AGN and quasars. However, clustering measurements depend strongly on the "mask" that removes low-quality data and describes the sky and selection function. We find that applying a robust, conservative mask to WISE-selected quasars yields a weaker but still significant difference in the bias between obscured and unobscured quasars. These findings are consistent with results from previous Spitzer surveys, and removes any scale dependence of the bias. For obscured quasars with $\langle z \rangle = 0.99$ we measure a bias of $b_q = 2.67 \pm 0.16$, corresponding to a halo mass of $\log (M_h / M_{\odot} h^{-1}) = 13.3 \pm 0.1$, while for unobscured sources with $\langle z \rangle = 1.04$ we find $b_q = 2.04 \pm 0.17$ with a halo mass $\log (M_h / M_{\odot} h^{-1} )= 12.8 \pm 0.1$. This improved measurement indicates that WISE-selected obscured quasars reside in halos only a few times more massive than the halos of their unobscured counterparts, a reduction in the factor of $\sim$10 larger halo mass as has been previously reported using WISE-selected samples. Additionally, an abundance matching analysis yields lifetimes for both obscured and unobscured quasar phases on the order of a few 100 Myr ($\sim$ 1\% of the Hubble time) --- however, the obscured phase lasts roughly twice as long, in tension with many model predictions.
Weighing obscured and unobscured quasar hosts with the CMB
M. A. DiPompeo,A. D. Myers,R. C. Hickox,J. E. Geach,G. Holder,K. N. Hainline,S. W. Hall
Physics , 2014, DOI: 10.1093/mnras/stu2341
Abstract: We cross-correlate a cosmic microwave background (CMB) lensing map with the projected space densities of quasars to measure the bias and halo masses of a quasar sample split into obscured and unobscured populations, the first application of this method to distinct quasar subclasses. Several recent studies of the angular clustering of obscured quasars have shown that these objects likely reside in higher-mass halos compared to their unobscured counterparts. This has important implications for models of the structure and geometry of quasars, their role in growing supermassive black holes, and mutual quasar/host galaxy evolution. However, the magnitude and significance of this difference has varied from study to study. Using data from \planck, \wise, and SDSS, we follow up on these results using the independent method of CMB lensing cross-correlations. The region and sample are identical to that used for recent angular clustering measurements, allowing for a direct comparison of the CMB-lensing and angular clustering methods. At $z \sim 1$, we find that the bias of obscured quasars is $b_q = 2.57 \pm 0.24$, while that of unobscured quasars is $b_q = 1.89 \pm 0.19$. This corresponds to halo masses of $\log (M_h / M_{\odot} h^{-1}) = 13.24_{-0.15}^{+0.14}$ (obscured) and $\log (M_h / M_{\odot} h^{-1}) = 12.71_{-0.13}^{+0.15}$ (unobscured). These results agree well with with those from angular clustering (well within $1\sigma$), and confirm that obscured quasars reside in host halos $\sim$3 times as massive as halos hosting unobscured quasars. This implies that quasars spend a significant portion of their lifetime in an obscured state, possibly more than one half of the entire active phase.
Persistence of Natural Killer (NK) cell lymphocytosis with hyposplenism without development of leukaemia
Sujoy Khan, K Myers
BMC Clinical Pathology , 2005, DOI: 10.1186/1472-6890-5-8
Abstract: We report a lady with a benign clinical course over 10 years and persistent CD8+/CD3-/CD57+/CD16+ LGL proliferation with presence of Howell-Jolly bodies (functional hyposplenism), an association not previously described.We discuss the possible causes of clonal expansion and conclude that this may be part of the spectrum of immune dysregulation associated with NK-cell lymphocytosis.The lymphoproliferative disease of granular lymphocytes (LDGL) results from the chronic proliferation of large granular lymphocytes (LGL) that may result from antigenic stimulation1,2. Natural Killer (NK) cells constitute approximately 15% of the peripheral blood mononuclear cell fraction. NK cells lack both CD3 and T-cell receptor expression, majority express CD56 and/or CD16 (Fcγ receptor). Granular lymphocytosis greater than 2,000/μL lasting for more than 6 months is regarded as the criteria to define the disease [1,2]. Patients with chronic, indolent NK lymphocytosis may develop cytopenias, splenomegaly, vasculitic skin lesions, and peripheral neuropathy [3]. We discuss a unique case of chronic, indolent NK lymphocytosis who presented with severe hyposplenism and has not developed leukaemia over a decade.A 46-year-old lady was referred to the haematology clinic for evaluation of lymphocytosis in May 1993. She had severe lethargy and intermittent right upper abdominal discomfort without any significant loss in weight. Her past medical history included essential hypertension controlled on atenolol 100 mg once daily and was also on frusemide 40 mg once daily. She had no significant surgical history other than having undergone cholecystectomy in 1972. She had never smoked nor consumed alcohol. Physical examination showed no evidence of lymphadenopathy. Complete blood count showed normal haemoglobin concentration 14.8 g/dl, macrocytosis (MCV 100.1), raised white cell count at 13.4 × 109/L, lymphocytosis (absolute number 6.3 × 109/L), and normal neutrophil count (absolute number 5.6 × 109/L)
Fecal Incontinence: Prevalence, Severity, and Quality of Life Data from an Outpatient Gastroenterology Practice
Eva H. Alsheik,Thomas Coyne,Sara K. Hawes,Laleh Merikhi,Scott P. Naples,Nandhakumar Kanagarajan,James C. Reynolds,Scott E. Myers,Asyia S. Ahmad
Gastroenterology Research and Practice , 2012, DOI: 10.1155/2012/947694
Abstract: Background. The prevalence of fecal incontinence varies tremendously as a result of inadequate data collection methods. Few office-based studies have assessed the prevalence of fecal incontinence and none have looked at modifiable risk factors or effect on quality of life. Design, Settings, Patients, and Main Outcome Measures. Five hundred patients who visited our inner city, university-based gastroenterology practice, were asked about symptoms of fecal incontinence. We also retrospectively reviewed 500 charts to identify the frequency of patient-physician reporting of fecal incontinence. Results. Of the 500 patients that were directly questioned, 58 (12%, 43 women, 15 men) admitted to fecal incontinence compared to 12 (2.4%) in the retrospective arm. Patients with fecal incontinence and loose/watery stool reported the lowest quality of life scores. While the average severity score was similar between men and women, women had a significantly lower average quality of life score (3.04 versus 2.51; <0.03). Conclusions. The identification of fecal incontinence increases when patients are directly questioned. Identifying and treating patients with loose stool is a potential strategy to improve quality of life in this patient population. In men and women with similar severity of fecal incontinence, women have a significantly lower quality of life.
Nanomechanical Measurements of Magnetostriction and Magnetic Anisotropy in (Ga,Mn)As
S. C. Masmanidis,H. X. Tang,E. B. Myers,Mo Li,K. De Greve,G. Vermeulen,W. Van Roy,M. L. Roukes
Physics , 2005, DOI: 10.1103/PhysRevLett.95.187206
Abstract: A (Ga,Mn)As nanoelectromechanical resonator is used to obtain the first direct measurement of magnetostriction in a dilute magnetic semiconductor. Field-dependent magnetoelastic stress induces shifts in resonance frequency that can be discerned with a high resolution electromechanical transduction scheme. By monitoring the field dependence, the magnetostriction and anisotropy field constants can be simultaneously mapped over a wide range of temperatures. These results, when compared with theoretical predictions, appear to provide insight into a unique form of magnetoelastic behavior mediated by holes.
Independent Electronic and Magnetic Doping in (Ga,Mn)As Based Digital Ferromagnetic Heterostructures
E. Johnston-Halperin,J. A. Schuller,C. S. Gallinat,T. C. Kreutz,R. C. Myers,R. K. Kawakami,H. Knotz,A. C. Gossard,D. D. Awschalom
Physics , 2003, DOI: 10.1103/PhysRevB.68.165328
Abstract: Ferromagnetic semiconductors promise the extension of metal-based spintronics into a material system that combines widely tunable electronic, optical, and magnetic properties. Here, we take steps towards realizing that promise by achieving independent control of electronic doping in the ferromagnetic semiconductor (Ga,Mn)As. Samples are comprised of superlattices of 0.5 monolayer (ML) MnAs alternating with 20 ML GaAs and are grown by low temperature (230 C) atomic layer epitaxy (ALE). This allows for the reduction of excess As incorporation and hence the number of charge-compensating As-related defects. We grow a series of samples with either Be or Si doping in the GaAs spacers (p- and n-type dopants, respectively), and verify their structural quality by in situ reflection high-energy electron diffraction (RHEED) and ex situ x-ray diffraction. Magnetization measurements reveal ferromagnetic behavior over the entire doping range, and show no sign of MnAs precipitates. Finally, magneto-transport shows the giant planar Hall effect and strong (20%) resistance fluctuations that may be related to domain wall motion.
Monte Carlo Simulation of the Photon-Tagger Focal-Plane Electronics at the MAX IV Laboratory
L. S. Myers,G. Feldman,K. G. Fissum,L. Isaksson,M. A. Kovash,A. M. Nathan,R. E. Pywell,B. Schr?der
Physics , 2013, DOI: 10.1016/j.nima.2013.08.032
Abstract: Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory have been investigated using the novel approach of Monte Carlo simulation. Results are compared to analytical calculations as well as experimental data for both specialized testing and production running to demonstrate a thorough understanding of the behavior of the detector system.
The Spitzer Space Telescope Survey of the Orion A & B Molecular Clouds - Part I: A Census of Dusty Young Stellar Objects and a Study of their Mid-IR Variability
S. T. Megeath,R. Gutermuth,J. Muzerolle,E. Kryukova,K. Flaherty,J. Hora,L E. Allen,L. Hartmann,P. C. Myers,J. L. Pipher,J. Stauffer,E. T. Young,G. G. Fazio
Physics , 2012, DOI: 10.1088/0004-6256/144/6/192
Abstract: We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments onboard Spitzer. In total, five distinct fields were mapped covering 9 sq. degrees in five mid-IR bands spanning 3-24 microns. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630 and 1622 dark clouds, and the NGC 2023, 2024, 2068 and 2071 nebulae. These data are merged with the 2MASS point source catalog to generate a catalog of eight band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in 2-3 epochs over 6 months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5 micron bands. We find that 50% of the dusty YSOs show variability. The variations are typically small (0.2 mag.) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8 and 8 micron variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots.
The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects
S. T. Megeath,R. Gutermuth,J. Muzerolle,E. Kryukova,J. L. Hora,L. E. Allen,K. Flaherty,L. Hartmann,P. C. Myers,J. L. Pipher,J. Stauffer,E. T. Young,G. G. Fazio
Physics , 2015,
Abstract: We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups show that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only $\sim 2$ Myr in age. We find the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or by dynamical interactions in dense, clustered regions.
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