140 research outputs found
On intrinsically knotted or completely 3-linked graphs
We say that a graph is intrinsically knotted or completely 3-linked if every
embedding of the graph into the 3-sphere contains a nontrivial knot or a
3-component link any of whose 2-component sublink is nonsplittable. We show
that a graph obtained from the complete graph on seven vertices by a finite
sequence of -exchanges and -exchanges is a
minor-minimal intrinsically knotted or completely 3-linked graph.Comment: 17 pages, 9 figure
X-rays from the Power Sources of the Cepheus A Star-Forming Region
We report an observation of X-ray emission from the exciting region of
Cepheus A with the Chandra/ACIS instrument. What had been an unresolved X-ray
source comprising the putative power sources is now resolved into at least 3
point-like sources, each with similar X-ray properties and differing radio and
submillimeter properties. The sources are HW9, HW3c, and a new source that is
undetected at other wavelengths "h10." They each have inferred X-ray
luminosities >= 10^31 erg s^-1 with hard spectra, T >= 10^7 K, and high
low-energy absorption equivalent to tens to as much as a hundred magnitudes of
visual absorption. The star usually assumed to be the most massive and
energetic, HW2, is not detected with an upper limit about 7 times lower than
the detections. The X-rays may arise via thermal bremsstrahlung in diffuse
emission regions associated with a gyrosynchrotron source for the radio
emission, or they could arise from powerful stellar winds. We also analyzed the
Spitzer/IRAC mid-IR observation from this star-formation region and present the
X-ray results and mid-IR classifications of the nearby stars. HH 168 is not as
underluminous in X-rays as previously reported.Comment: Accepted in the ApJ, 30 pages, 11 figures, in one .pdf fil
Relationship between nerve fiber layer defect and the presence of epiretinal membrane in a Japanese population: The JPHC-NEXT Eye Study
The study subjects were residents of Chikusei city, Japan, aged 40 years or older who attended annual health check-up programs and participated in the JPHC-NEXT Eye Study which performed non-mydriatic fundus photography of both eyes. The relationship of glaucomatous fundus changes such as optic disc cupping (cup to disc ratio ≥ 0.7) and retinal nerve fiber layer defect (NFLD) with the presence of epiretinal membrane (ERM) were examined cross-sectionally. A total of 1990 persons gave consent to participate in this study in 2013. The overall prevalence of ERM was 12.9%. Of these, 1755 had fundus photographs of sufficient quality and no history of intraocular surgery (mean age: 62.3 ± 10.0 years). After adjusting for age, sex and refractive error, NFLD was positively associated with the presence of ERM (odds ratio [OR]: 2.48; 95% confidence interval [CI]: 1.24, 4.96; P = 0.010), but optic disc cupping was not (OR: 1.33; CI: 0.71, 2.48; P = 0.37). The results did not necessarily suggest an association between glaucoma and ERM, but indicated an association between NFLD and ERM
Elucidating colorectal cancer-associated bacteria through profiling of minimally perturbed tissue-associated microbiota
Sequencing-based interrogation of gut microbiota is a valuable approach for detecting microbes associated with colorectal cancer (CRC); however, such studies are often confounded by the effect of bowel preparation. In this study, we evaluated the viability of identifying CRC-associated mucosal bacteria through centimeter-scale profiling of the microbiota in tumors and adjacent noncancerous tissue from eleven patients who underwent colonic resection without preoperative bowel preparation. High-throughput 16S rRNA gene sequencing revealed that differences between on- and off-tumor microbiota varied considerably among patients. For some patients, phylotypes affiliated with genera previously implicated in colorectal carcinogenesis, as well as genera with less well-understood roles in CRC, were enriched in tumor tissue, whereas for other patients, on- and off-tumor microbiota were very similar. Notably, the enrichment of phylotypes in tumor-associated mucosa was highly localized and no longer apparent even a few centimeters away from the tumor. Through short-term liquid culturing and metagenomics, we further generated more than one-hundred metagenome-assembled genomes, several representing bacteria that were enriched in on-tumor samples. This is one of the first studies to analyze largely unperturbed mucosal microbiota in tissue samples from the resected colons of unprepped CRC patients. Future studies with larger cohorts are expected to clarify the causes and consequences of the observed variability in the emergence of tumor-localized microbiota among patients
A Large X-ray Flare from a Single Weak-lined T Tauri Star TWA-7 Detected with MAXI GSC
We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7
detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image
(MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of
ergs cm s in 2--20 keV band during the scan
transit starting at UT 2010-09-07 18:24:30.The estimated X-ray luminosity at
the scan in the energy band is 3 ergs s,indicating that
the event is among the largest X-ray flares fromT Tauri stars.Since MAXI GSC
monitors a target only during a scan transit of about a minute per 92 min
orbital cycle, the luminosity at the flare peak might have been higher than
that detected. At the scan transit, we observed a high X-ray-to-bolometric
luminosity ratio, log = ; i.e., the
X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has
neither an accreting disk nor a binary companion, the observed event implies
that none of those are essential to generate such big flares in T Tauri stars.Comment: 4 pages, 2 figures, 1 table accepted for publication in PAS
- …