4,094 research outputs found
The Discrete Fundamental Group of the Associahedron, and the Exchange Module
The associahedron is an object that has been well studied and has numerous
applications, particularly in the theory of operads, the study of non-crossing
partitions, lattice theory and more recently in the study of cluster algebras.
We approach the associahedron from the point of view of discrete homotopy
theory. We study the abelianization of the discrete fundamental group, and show
that it is free abelian of rank . We also find a combinatorial
description for a basis of this rank. We also introduce the exchange module of
the type cluster algebra, used to model the relations in the cluster
algebra. We use the discrete fundamental group to the study of exchange module,
and show that it is also free abelian of rank .Comment: 16 pages, 4 figure
A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau
The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in
its radial velocity (RV) variations measured at infrared (IR) and optical
wavelengths. We find that these observations are consistent with a massive
planet in a ~9-day period orbit. These results are based on 71 IR RV
measurements of this system obtained over 5 years, and on 26 optical RV
measurements obtained over 9 years. CI Tau was also observed photometrically in
the optical on 34 nights over ~one month in 2012. The optical RV data alone are
inadequate to identify an orbital period, likely the result of star spot and
activity induced noise for this relatively small dataset. The infrared RV
measurements reveal significant periodicity at ~9 days. In addition, the full
set of optical and IR RV measurements taken together phase coherently and with
equal amplitudes to the ~9 day period. Periodic radial velocity signals can in
principle be produced by cool spots, hot spots, and reflection of the stellar
spectrum off the inner disk, in addition to resulting from a planetary
companion. We have considered each of these and find the planet hypothesis most
consistent with the data. The radial velocity amplitude yields an Msin(i) of
~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the
circumstellar disk inclination from the literature, we find a planet mass of
~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.Comment: 61 pages, 13 figures, accepted for publication in The Astrophysical
Journa
The Relation Between Galaxy ISM and Circumgalactic OVI Gas Kinematics Derived from Observations and CDM Simulations
We present the first galaxy-OVI absorption kinematic study for 20 absorption
systems (EW>0.1~{\AA}) associated with isolated galaxies (0.150.55) that
have accurate redshifts and rotation curves obtained using Keck/ESI. Our sample
is split into two azimuthal angle bins: major axis () and
minor axis (). OVI absorption along the galaxy major axis is
not correlated with galaxy rotation kinematics, with only 1/10 systems that
could be explained with rotation/accretion models. This is in contrast to
co-rotation commonly observed for MgII absorption. OVI along the minor axis
could be modeled by accelerating outflows but only for small opening angles,
while the majority of the OVI is decelerating. Along both axes, stacked OVI
profiles reside at the galaxy systemic velocity with the absorption kinematics
spanning the entire dynamical range of their galaxies. The OVI found in AMR
cosmological simulations exists within filaments and in halos of ~50 kpc
surrounding galaxies. Simulations show that major axis OVI gas inflows along
filaments and decelerates as it approaches the galaxy while increasing in its
level of co-rotation. Minor axis outflows in the simulations are effective
within 50-75 kpc beyond that they decelerate and fall back onto the galaxy.
Although the simulations show clear OVI kinematic signatures they are not
directly comparable to observations. When we compare kinematic signatures
integrated through the entire simulated galaxy halo we find that these
signatures are washed out due to full velocity distribution of OVI throughout
the halo. We conclude that OVI alone does not serve as a useful kinematic
indicator of gas accretion, outflows or star-formation and likely best probes
the halo virial temperature.Comment: 24 pages, 21 figures, 4 tables. Accepted to ApJ on November 14, 201
A 850-GHz waveguide receiver employing a niobium SIS junction fabricated on a 1-μm Si_3N_4 membrane
We report on a 850-GHz superconducting-insulator-superconducting (SIS) heterodyne receiver employing an RF-tuned niobium tunnel junction with a current density of 14 kA/cm^2, fabricated on a 1-µm Si_3N_4 supporting membrane. Since the mixer is designed to be operated well above the superconducting gap frequency of niobium (2Δ/h ≈ 690 GHz), special care has been taken to minimize niobium transmission-line losses. Both Fourier transform spectrometer (FTS) measurements of the direct detection performance and calculations of the IF output noise with the mixer operating in heterodyne mode, indicate an absorption loss in the niobium film of about 6.8 dB at 822 GHz. These results are in reasonably good agreement with the loss predicted by the Mattis-Bardeen theory in the extreme anomalous limit. From 800 to 830 GHz, we report uncorrected receiver noise temperatures of 518 or 514 K when we use Callen and Welton's law to calculate the input load temperatures. Over the same frequency range, the mixer has a 4-dB conversion loss and 265 K ± 10 K noise temperature. At 890 GHz, the sensitivity of the receiver has degraded to 900 K, which is primarily the result of increased niobium film loss in the RF matching network. When the mixer was cooled from 4.2 to 1.9 K, the receiver noise temperature improved about 20% 409-K double sideband (DSB). Approximately half of the receiver noise temperature improvement can be attributed to a lower mixer conversion loss, while the remainder is due to a reduction in the niobium film absorption loss. At 982 GHz, we measured a receiver noise temperature of 1916 K
High-efficiency endovascular gene delivery via therapeutic ultrasound
AbstractOBJECTIVESWe studied enhancement of local gene delivery to the arterial wall by using an endovascular catheter ultrasound (US).BACKGROUNDUltrasound exposure is standard for enhancement of in vitro gene delivery. We postulate that in vivo endovascular applications can be safely developed.METHODSWe used a rabbit model of arterial mechanical overdilation injury. After arterial overdilation, US catheters were introduced in bilateral rabbit femoral arteries and perfused with plasmid- or adenovirus-expressing blue fluorescent protein (BFP) or phosphate buffered saline. One side received endovascular US (2 MHz, 50 W/cm2, 16 min), and the contralateral artery did not.RESULTSRelative to controls, US exposure enhanced BFP expression measured via fluorescence 12-fold for plasmid (1,502.1 ± 927.3 vs. 18,053.9 ± 11,612 μm2, p < 0.05) and 19-fold for adenovirus (877.1 ± 577.7 vs. 17,213.15 ± 3,892 μm2, p < 0.05) while increasing cell death for the adenovirus group only (26 ± 5.78% vs. 13 ± 2.55%, p < 0.012).CONCLUSIONSEndovascular US enhanced vascular gene delivery and increased the efficiency of nonviral platforms to levels previously attained only by adenoviral strategies
Codon-precise, synthetic, antibody fragment libraries built using automated hexamer codon additions and validated through next generation sequencing
We have previously described ProxiMAX, a technology that enables the fabrication of precise, combinatorial gene libraries via codon-by-codon saturation mutagenesis. ProxiMAX was originally performed using manual, enzymatic transfer of codons via blunt-end ligation. Here we present Colibraâ„¢: an automated, proprietary version of ProxiMAX used specifically for antibody library generation, in which double-codon hexamers are transferred during the saturation cycling process. The reduction in process complexity, resulting library quality and an unprecedented saturation of up to 24 contiguous codons are described. Utility of the method is demonstrated via fabrication of complementarity determining regions (CDR) in antibody fragment libraries and next generation sequencing (NGS) analysis of their quality and diversity
Was COVID-19 associated with worsening inequities in stroke treatment and outcomes?
Background COVID-19 stressed hospitals and may have disproportionately affected the stroke outcomes and treatment of Black and Hispanic individuals. Methods and Results This retrospective study used 100% Medicare Provider Analysis and Review file data from between 2016 and 2020. We used interrupted time series analyses to examine whether the COVID-19 pandemic exacerbated disparities in stroke outcomes and reperfusion therapy. Among 1 142 560 hospitalizations for acute ischemic strokes, 90 912 (8.0%) were Hispanic individuals; 162 752 (14.2%) were non-Hispanic Black individuals; and 888 896 (77.8%) were non-Hispanic White individuals. The adjusted odds of mortality increased by 51% (adjusted odds ratio [aOR], 1.51 [95% CI, 1.34-1.69]
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