Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments

We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction.Comment: Conference Proceeding (Trends in NanoTechnology 2011, Tenerife SPAIN); Nanoscale Research Letters, (2012) 7:25

Proper motions of the HH1 jet

We describe a new method for determining proper motions of extended objects, and a pipeline developed for the application of this method. We then apply this method to an analysis of four epochs of [S~II] HST images of the HH~1 jet (covering a period of $\sim 20$~yr). We determine the proper motions of the knots along the jet, and make a reconstruction of the past ejection velocity time-variability (assuming ballistic knot motions). This reconstruction shows an "acceleration" of the ejection velocities of the jet knots, with higher velocities at more recent times. This acceleration will result in an eventual merging of the knots in $\sim 450$~yr and at a distance of $\sim 80"$ from the outflow source, close to the present-day position of HH~1.Comment: 12 pages, 8 figure

Real-Time Road Hazard Information System

Infrastructure is a significant factor in economic growth for systems of government. In order to increase economic productivity, maintaining infrastructure quality is essential. One of the elements of infrastructure is roads. Roads are means which help local and national economies be more productive. Furthermore, road damage such as potholes, debris, or cracks is the cause of many on-road accidents that have cost the lives of many drivers. In this paper, we propose a system that uses Convolutional Neural Networks to detect road degradations without data pre-processing. We utilize the state-of-the-art object detection algorithm, YOLO detector for the system. First, we developed a basic system working on data collecting, pre-processing, and classification. Secondly, we improved the classification performance achieving 97.98% in the overall model testing, and then we utilized pixel-level classification and detection with a method called semantic segmentation. We were able to achieve decent results using this method to detect and classify four different classes (Manhole, Pothole, Blurred Crosswalk, Blurred Street Line). We trained a segmentation model that recognizes the four classes mentioned above and achieved great results with this model allowing the machine to effectively and correctly identify and classify our four classes in an image. Although we obtained excellent accuracy from the detectors, these do not perform particularly well on embedded systems due to their network size. Therefore, we opted for a smaller, less accurate detector that will run in real time on a cheap embedded system, like the Google Coral Dev Board, without needing a powerful and expensive GPU

Decline of genetic diversity in ancient domestic stallions in Europe.

Present-day domestic horses are immensely diverse in their maternally inherited mitochondrial DNA, yet they show very little variation on their paternally inherited Y chromosome. Although it has recently been shown that Y chromosomal diversity in domestic horses was higher at least until the Iron Age, when and why this diversity disappeared remain controversial questions. We genotyped 16 recently discovered Y chromosomal single-nucleotide polymorphisms in 96 ancient Eurasian stallions spanning the early domestication stages (Copper and Bronze Age) to the Middle Ages. Using this Y chromosomal time series, which covers nearly the entire history of horse domestication, we reveal how Y chromosomal diversity changed over time. Our results also show that the lack of multiple stallion lineages in the extant domestic population is caused by neither a founder effect nor random demographic effects but instead is the result of artificial selection-initially during the Iron Age by nomadic people from the Eurasian steppes and later during the Roman period. Moreover, the modern domestic haplotype probably derived from another, already advantageous, haplotype, most likely after the beginning of the domestication. In line with recent findings indicating that the Przewalski and domestic horse lineages remained connected by gene flow after they diverged about 45,000 years ago, we present evidence for Y chromosomal introgression of Przewalski horses into the gene pool of European domestic horses at least until medieval times

The 2HWC HAWC Observatory Gamma Ray Catalog

We present the first catalog of TeV gamma-ray sources realized with the recently completed High Altitude Water Cherenkov Observatory (HAWC). It is the most sensitive wide field-of-view TeV telescope currently in operation, with a 1-year survey sensitivity of ~5-10% of the flux of the Crab Nebula. With an instantaneous field of view >1.5 sr and >90% duty cycle, it continuously surveys and monitors the sky for gamma ray energies between hundreds GeV and tens of TeV. HAWC is located in Mexico at a latitude of 19 degree North and was completed in March 2015. Here, we present the 2HWC catalog, which is the result of the first source search realized with the complete HAWC detector. Realized with 507 days of data and represents the most sensitive TeV survey to date for such a large fraction of the sky. A total of 39 sources were detected, with an expected contamination of 0.5 due to background fluctuation. Out of these sources, 16 are more than one degree away from any previously reported TeV source. The source list, including the position measurement, spectrum measurement, and uncertainties, is reported. Seven of the detected sources may be associated with pulsar wind nebulae, two with supernova remnants, two with blazars, and the remaining 23 have no firm identification yet.Comment: Submitted 2017/02/09 to the Astrophysical Journa

Highly responsive UV-photodetectors based on single electrospun TiO2 nanofibres

In this work we study the optoelectronic properties of individual TiO2 fibres produced through coupled sol-gel and electrospinning, by depositing them onto pre-patterned Ti/Au electrodes on SiO2/Si substrates. Transport measurements in the dark give a conductivity above 2*10^-5 S, which increases up to 8*10^-5 S in vacuum. Photocurrent measurements under UV-irradiation show high sensitivity (responsivity of 90 A/W for 375 nm wavelength) and a response time to illumination of ~ 5 s, which is superior to state-of-the-art TiO2-based UV photodetectors. Both responsivity and response speed are higher in air than in vacuum, due to oxygen adsorbed on the TiO2 surface which traps photoexcited free electrons in the conduction band, thus reducing the recombination processes. The photodetectors are sensitive to light polarization, with an anisotropy ratio of 12%. These results highlight the interesting combination of large surface area and low 1D transport resistance in electrospun TiO2 fibres. The simplicity of the sol-gel/electrospinning synthesis method, combined with a fast response and high responsivity makes them attractive candidates for UV-photodetection in ambient conditions. We anticipate their high (photo) conductance is also relevant for photocatalysis and dye-sensitized solar cells.Comment: 29 pages, 5 figures in the main text, 9 figures in the Supporting Information. in J. Mater. Chem. C, 201

Daily monitoring of TeV gamma-ray emission from Mrk 421, Mrk 501, and the Crab Nebula with HAWC

We present results from daily monitoring of gamma rays in the energy range $\sim0.5$ to $\sim100$ TeV with the first 17 months of data from the High Altitude Water Cherenkov (HAWC) Observatory. Its wide field of view of 2 steradians and duty cycle of $>95$% are unique features compared to other TeV observatories that allow us to observe every source that transits over HAWC for up to $\sim6$ hours each sidereal day. This regular sampling yields unprecedented light curves from unbiased measurements that are independent of seasons or weather conditions. For the Crab Nebula as a reference source we find no variability in the TeV band. Our main focus is the study of the TeV blazars Markarian (Mrk) 421 and Mrk 501. A spectral fit for Mrk 421 yields a power law index $\Gamma=2.21 \pm0.14_{\mathrm{stat}}\pm0.20_{\mathrm{sys}}$ and an exponential cut-off $E_0=5.4 \pm 1.1_{\mathrm{stat}}\pm 1.0_{\mathrm{sys}}$ TeV. For Mrk 501, we find an index $\Gamma=1.60\pm 0.30_{\mathrm{stat}} \pm 0.20_{\mathrm{sys}}$ and exponential cut-off $E_0=5.7\pm 1.6_{\mathrm{stat}} \pm 1.0_{\mathrm{sys}}$ TeV. The light curves for both sources show clear variability and a Bayesian analysis is applied to identify changes between flux states. The highest per-transit fluxes observed from Mrk 421 exceed the Crab Nebula flux by a factor of approximately five. For Mrk 501, several transits show fluxes in excess of three times the Crab Nebula flux. In a comparison to lower energy gamma-ray and X-ray monitoring data with comparable sampling we cannot identify clear counterparts for the most significant flaring features observed by HAWC.Comment: 18 pages, 10 figures, accepted for publication in The Astrophysical Journa

Fibrosis Severity as a Determinant of Cause-Specific Mortality in Patients With Advanced Nonalcoholic Fatty Liver Disease: A Multi-National Cohort Study

Background & Aims Little is known about the natural course of nonalcoholic fatty liver disease (NAFLD) with advanced fibrosis. We describe long-term outcomes and evaluate the effects of clinical and histologic parameters on disease progression in patients with advanced NAFLD. Methods We conducted a multi-national study of 458 patients with biopsy-confirmed NAFLD with bridging fibrosis (F3, n = 159) or compensated cirrhosis (222 patients with Child-Turcotte-Pugh scores of A5 and 77 patients with scores of A6), evaluated from April 1995 through November 2013 and followed until December 2016, death, or liver transplantation at hepatology centers in Spain, Australia, Hong Kong, and Cuba. Biopsies were re-evaluated and scored; demographic, clinical, laboratory, and pathology data for each patient were collected from the time of liver biopsy collection. Cox proportional and competing risk models were used to estimate rates of transplantation-free survival and major clinical events and to identify factors associated with outcomes. Results During a mean follow-up time of 5.5 years (range, 2.7–8.2 years), 37 patients died, 37 received liver transplants, 88 had initial hepatic decompensation events, 41 developed hepatocellular carcinoma, 14 had vascular events, and 30 developed nonhepatic cancers. A higher proportion of patients with F3 fibrosis survived transplantation-free for 10 years (94%; 95% confidence interval [CI], 86%–99%) than of patients with cirrhosis and Child-Turcotte-Pugh A5 (74%; 95% CI, 61%–89%) or Child-Turcotte-Pugh A6 (17%; 95% CI, 6%–29%). Patients with cirrhosis were more likely than patients with F3 fibrosis to have hepatic decompensation (44%; 95% CI, 32%–60% vs 6%, 95% CI, 2%–13%) or hepatocellular carcinoma (17%; 95% CI, 8%–31% vs 2.3%, 95% CI, 1%–12%). The cumulative incidence of vascular events was higher in patients with F3 fibrosis (7%; 95% CI, 3%–18%) than cirrhosis (2%; 95% CI, 0%–6%). The cumulative incidence of nonhepatic malignancies was higher in patients with F3 fibrosis (14%; 95% CI, 7%–23%) than cirrhosis (6%; 95% CI, 2%–15%). Death or transplantation, decompensation, and hepatocellular carcinoma were independently associated with baseline cirrhosis and mild (<33%) steatosis, whereas moderate alcohol consumption was associated with these outcomes only in patients with cirrhosis. Conclusions Patients with NAFLD cirrhosis have predominantly liver-related events, whereas those with bridging fibrosis have predominantly nonhepatic cancers and vascular events

Effective Rheology of Bubbles Moving in a Capillary Tube

We calculate the average volumetric flux versus pressure drop of bubbles moving in a single capillary tube with varying diameter, finding a square-root relation from mapping the flow equations onto that of a driven overdamped pendulum. The calculation is based on a derivation of the equation of motion of a bubble train from considering the capillary forces and the entropy production associated with the viscous flow. We also calculate the configurational probability of the positions of the bubbles.Comment: 4 pages, 1 figur