3,375 research outputs found
Analysis of the forming characteristics for Cu/Al bimetal tubes produced by the spinning process
Tube spinning technology represents a process with high forming precision and good flexibility and is increasingly being used in the manufacture of bimetal composite tubular structures. In the present study, a forming analysis of clad tube and base tube in spinning process was conducted through numerical simulations and experiments. There was an equivalent stress transition on the interface since the stress transmission was retarded from clad tube to base tube. The yield strength became a main consideration during a design bimetal composite tube. Meanwhile, the strain distributions in axial direction, tangential direction, and radial direction were also investigated to determine the deformation characteristics of each component. As the press amount increased, the strain of clad tube changed more than base tube. As the feed rate increased, the strain decreased in axial direction and tangential direction but almost unchanged in radial direction. Simultaneously, a method for controlling the wall thickness of the clad tube and the base tube is proposed. These results to guide the design of bimetal tube composite spinning process have the certain meanings
Statistics of X-ray flares of Sagittarius A*: evidence for solar-like self-organized criticality phenomenon
X-ray flares have routinely been observed from the supermassive black hole,
Sagittarius A (Sgr A), at our Galactic center. The nature of
these flares remains largely unclear, despite of many theoretical models. In
this paper, we study the statistical properties of the Sgr A X-ray
flares, by fitting the count rate (CR) distribution and the structure function
(SF) of the light curve with a Markov Chain Monte Carlo (MCMC) method. With the
3 million second \textit{Chandra} observations accumulated in the Sgr A
X-ray Visionary Project, we construct the theoretical light curves through
Monte Carlo simulations. We find that the keV X-ray light curve can be
decomposed into a quiescent component with a constant count rate of
count s and a flare component with a power-law
fluence distribution with . The duration-fluence correlation can also be modelled as a
power-law with (
confidence). These statistical properties are consistent with the theoretical
prediction of the self-organized criticality (SOC) system with the spatial
dimension . We suggest that the X-ray flares represent plasmoid
ejections driven by magnetic reconnection (similar to solar flares) in the
accretion flow onto the black hole.Comment: to appear in Ap
The Nature of Associated Absorption and the UV-X-ray Connection in 3C 288.1
We discuss new Hubble Space Telescope spectroscopy of the radio-loud quasar,
3C 288.1. The data cover ~590 A to ~1610 A in the quasar rest frame. They
reveal a wealth of associated absorption lines (AALs) with no accompanying
Lyman-limit absorption. The metallic AALs range in ionization from C III and N
III to Ne VIII and Mg X. We use these data and photoionization models to derive
the following properties of the AAL gas: 1) There are multiple ionization zones
within the AAL region, spanning a factor of at least ~50 in ionization
parameter. 2) The overall ionization is consistent with the ``warm'' X-ray
continuum absorbers measured in Seyfert 1 nuclei and other QSOs. However, 3)
the column densities implied by the AALs in 3C 288.1 are too low to produce
significant bound-free absorption at any UV-X-ray wavelengths. Substantial
X-ray absorption would require yet another zone, having a much higher
ionization or a much lower velocity dispersion than the main AAL region. 4) The
total hydrogen column density in the AAL gas is log N_H (cm-2)= 20.2. 5) The
metallicity is roughly half solar. 6) The AALs have deconvolved widths of ~900
km/s and their centroids are consistent with no shift from the quasar systemic
velocity (conservatively within +/-1000 km/s). 7) There are no direct
indicators of the absorber's location in our data, but the high ionization and
high metallicity both suggest a close physical relationship to the quasar/host
galaxy environment. Finally, the UV continuum shape gives no indication of a
``blue bump'' at higher energies. There is a distinct break of unknown origin
at ~1030 A, and the decline toward higher energies (with spectral index alpha =
-1.73, for f_nu ~ nu^alpha) is even steeper than a single power-law
interpolation from 1030 A to soft X-rays.Comment: 27 pages with figures and tables, in press with Ap
Ethanol Induced Disordering of Pancreatic Acinar Cell Endoplasmic Reticulum: An ER Stress/Defective Unfolded Protein Response Model.
Background & aimsHeavy alcohol drinking is associated with pancreatitis, whereas moderate intake lowers the risk. Mice fed ethanol long term show no pancreas damage unless adaptive/protective responses mediating proteostasis are disrupted. Pancreatic acini synthesize digestive enzymes (largely serine hydrolases) in the endoplasmic reticulum (ER), where perturbations (eg, alcohol consumption) activate adaptive unfolded protein responses orchestrated by spliced X-box binding protein 1 (XBP1). Here, we examined ethanol-induced early structural changes in pancreatic ER proteins.MethodsWild-type and Xbp1+/- mice were fed control and ethanol diets, then tissues were homogenized and fractionated. ER proteins were labeled with a cysteine-reactive probe, isotope-coded affinity tag to obtain a novel pancreatic redox ER proteome. Specific labeling of active serine hydrolases in ER with fluorophosphonate desthiobiotin also was characterized proteomically. Protein structural perturbation by redox changes was evaluated further in molecular dynamic simulations.ResultsEthanol feeding and Xbp1 genetic inhibition altered ER redox balance and destabilized key proteins. Proteomic data and molecular dynamic simulations of Carboxyl ester lipase (Cel), a unique serine hydrolase active within ER, showed an uncoupled disulfide bond involving Cel Cys266, Cel dimerization, ER retention, and complex formation in ethanol-fed, XBP1-deficient mice.ConclusionsResults documented in ethanol-fed mice lacking sufficient spliced XBP1 illustrate consequences of ER stress extended by preventing unfolded protein response from fully restoring pancreatic acinar cell proteostasis during ethanol-induced redox challenge. In this model, orderly protein folding and transport to the secretory pathway were disrupted, and abundant molecules including Cel with perturbed structures were retained in ER, promoting ER stress-related pancreas pathology
Galaxy Zoo: dust lane early-type galaxies are tracers of recent, gas-rich minor mergers
We present the second of two papers concerning the origin and evolution of
local early-type galaxies exhibiting dust features. We use optical and radio
data to examine the nature of active galactic nucleus (AGN) activity in these
objects, and compare these with a carefully constructed control sample. We find
that dust lane early-type galaxies are much more likely to host emission-line
AGN than the control sample galaxies. Moreover, there is a strong correlation
between radio and emission-line AGN activity in dust lane early-types, but not
the control sample. Dust lane early-type galaxies show the same distribution of
AGN properties in rich and poor environments, suggesting a similar triggering
mechanism. By contrast, this is not the case for early-types with no dust
features. These findings strongly suggest that dust lane early-type galaxies
are starburst systems formed in gas-rich mergers. Further evidence in support
of this scenario is provided by enhanced star formation and black hole
accretion rates in these objects. Dust lane early-types therefore represent an
evolutionary stage between starbursting and quiescent galaxies. In these
objects, the AGN has already been triggered but has not as yet completely
destroyed the gas reservoir required for star formation.Comment: 11 pages, 18 figures, 4 tables, MNRAS (Accepted for publication- 2012
January 19
The Vaginal Microbiome: Disease, Genetics and the Environment
The vagina is an interactive interface between the host and the environment. Its surface is covered by a protective epithelium colonized by bacteria and other microorganisms. The ectocervix is nonsterile, whereas the endocervix and the upper genital tract are assumed to be sterile in healthy women. Therefore, the cervix serves a pivotal role as a gatekeeper to protect the upper genital tract from microbial invasion and subsequent reproductive pathology. Microorganisms that cross this barrier can cause preterm labor, pelvic inflammatory disease, and other gynecologic and reproductive disorders. Homeostasis of the microbiome in the vagina and ectocervix plays a paramount role in reproductive health. Depending on its composition, the microbiome may protect the vagina from infectious or non-infectious diseases, or it may enhance its susceptibility to them. Because of the nature of this organ, and the fact that it is continuously colonized by bacteria from birth to death, it is virtually certain that this rich environment evolved in concert with its microbial flora. Specific interactions dictated by the genetics of both the host and microbes are likely responsible for maintaining both the environment and the microbiome. However, the genetic basis of these interactions in both the host and the bacterial colonizers is currently unknown. _Lactobacillus_ species are associated with vaginal health, but the role of these species in the maintenance of health is not yet well defined. Similarly, other species, including those representing minor components of the overall flora, undoubtedly influence the ability of potential pathogens to thrive and cause disease. Gross alterations in the vaginal microbiome are frequently observed in women with bacterial vaginosis, but the exact etiology of this disorder is still unknown. There are also implications for vaginal flora in non-infectious conditions such as pregnancy, pre-term labor and birth, and possibly fertility and other aspects of women’s health. Conversely, the role of environmental factors in the maintenance of a healthy vaginal microbiome is largely unknown. To explore these issues, we have proposed to address the following questions:

*1.	Do the genes of the host contribute to the composition of the vaginal microbiome?* We hypothesize that genes of both host and bacteria have important impacts on the vaginal microbiome. We are addressing this question by examining the vaginal microbiomes of mono- and dizygotic twin pairs selected from the over 170,000 twin pairs in the Mid-Atlantic Twin Registry (MATR). Subsequent studies, beyond the scope of the current project, may investigate which host genes impact the microbial flora and how they do so.
*2.	What changes in the microbiome are associated with common non-infectious pathological states of the host?* We hypothesize that altered physiological (e.g., pregnancy) and pathologic (e.g., immune suppression) conditions, or environmental exposures (e.g., antibiotics) predictably alter the vaginal microbiome. Conversely, certain vaginal microbiome characteristics are thought to contribute to a woman’s risk for outcomes such as preterm delivery. We are addressing this question by recruiting study participants from the ~40,000 annual clinical visits to women’s clinics of the VCU Health System.
*3.	What changes in the vaginal microbiome are associated with relevant infectious diseases and conditions?* We hypothesize that susceptibility to infectious disease (e.g. HPV, _Chlamydia_ infection, vaginitis, vaginosis, etc.) is impacted by the vaginal microbiome. In turn, these infectious conditions clearly can affect the ability of other bacteria to colonize and cause pathology. Again, we are exploring these issues by recruiting participants from visitors to women’s clinics in the VCU Health System.

Three kinds of sequence data are generated in this project: i) rDNA sequences from vaginal microbes; ii) whole metagenome shotgun sequences from vaginal samples; and iii) whole genome shotgun sequences of bacterial clones selected from vaginal samples. The study includes samples from three vaginal sites: mid-vaginal, cervical, and introital. The data sets also include buccal and perianal samples from all twin participants. Samples from these additional sites are used to test the hypothesis of a per continuum spread of bacteria in relation to vaginal health. An extended set of clinical metadata associated with these sequences are deposited with dbGAP. We have currently collected over 4,400 samples from ~100 twins and over 450 clinical participants. We have analyzed and deposited data for 480 rDNA samples, eight whole metagenome shotgun samples, and over 50 complete bacterial genomes. These data are available to accredited investigators according to NIH and Human Microbiome Project (HMP) guidelines. The bacterial clones are deposited in the Biodefense and Emerging Infections Research Resources Repository ("http://www.beiresources.org/":http://www.beiresources.org/). 

In addition to the extensive sequence data obtained in this study, we are collecting metadata associated with each of the study participants. Thus, participants are asked to complete an extensive health history questionnaire at the time samples are collected. Selected clinical data associated with the visit are also obtained, and relevant information is collected from the medical records when available. This data is maintained securely in a HIPAA-compliant data system as required by VCU’s Institutional Review Board (IRB). The preponderance of these data (i.e., that judged appropriate by NIH staff and VCU’s IRB are deposited at dbGAP ("http://www.ncbi.nlm.nih.gov/gap":http://www.ncbi.nlm.nih.gov/gap). Selected fields of this data have been identified by NIH staff as ‘too sensitive’ and are not available in dbGAP. Individuals requiring access to these data fields are asked to contact the PI of this project or NIH Program Staff. 

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