585 research outputs found
Advanced Structures and Composites Center_Aerosol Box Notes & Photographs
Notes regarding an early prototype of an aerosol box produced by the University of Maine Advanced Structures and Composites Center in response to a need from front line medical staff when treating COVID-19. The design didn\u27t ultimately make it into production.
Also, including as supplementary content are photographs of the box taken by David F. Erb Jr., Senior R&D Program Manager, Advanced Structures and Composites Center
A bacteriophage tubulin harnesses dynamic instability to center DNA in infected cells.
Dynamic instability, polarity, and spatiotemporal organization are hallmarks of the microtubule cytoskeleton that allow formation of complex structures such as the eukaryotic spindle. No similar structure has been identified in prokaryotes. The bacteriophage-encoded tubulin PhuZ is required to position DNA at mid-cell, without which infectivity is compromised. Here, we show that PhuZ filaments, like microtubules, stochastically switch from growing in a distinctly polar manner to catastrophic depolymerization (dynamic instability) both in vitro and in vivo. One end of each PhuZ filament is stably anchored near the cell pole to form a spindle-like array that orients the growing ends toward the phage nucleoid so as to position it near mid-cell. Our results demonstrate how a bacteriophage can harness the properties of a tubulin-like cytoskeleton for efficient propagation. This represents the first identification of a prokaryotic tubulin with the dynamic instability of microtubules and the ability to form a simplified bipolar spindle
Stressor- and Corticotropin releasing Factor-induced Reinstatement and Active Stress-related Behavioral Responses are Augmented Following Long-access Cocaine Self-administration by Rats
Rationale Stressful events during periods of drug abstinence likely contribute to relapse in cocaine-dependent individuals. Excessive cocaine use may increase susceptibility to stressor-induced relapse through alterations in brain corticotropin-releasing factor (CRF) responsiveness.
Objectives This study examined stressor- and CRF-induced cocaine seeking and other stress-related behaviors in rats with different histories of cocaine self-administration (SA).
Materials and methods Rats self-administered cocaine under short-access (ShA; 2 h daily) or long-access (LgA; 6 h daily) conditions for 14 days or were provided access to saline and were tested for reinstatement by a stressor (electric footshock), cocaine or an icv injection of CRF and for behavioral responsiveness on the elevated plus maze, in a novel environment and in the light–dark box after a 14- to 17-day extinction/withdrawal period.
Results LgA rats showed escalating patterns of cocaine SA and were more susceptible to reinstatement by cocaine, EFS, or icv CRF than ShA rats. Overall, cocaine SA increased activity in the center field of a novel environment, on the open arms of the elevated plus maze, and in the light compartment of a light–dark box. In most cases, the effects of cocaine SA were dependent on the pattern/amount of cocaine intake with statistically significant differences from saline self-administering controls only observed in LgA rats.
Conclusions When examined after several weeks of extinction/ withdrawal, cocaine SA promotes a more active pattern of behavior during times of stress that is associated with a heightened susceptibility to stressor-induced cocaine-seeking behavior and may be the consequence of augmented CRF regulation of addiction-related neurocircuitry
The Physical Nature of Rest-UV Galaxy Morphology During the Peak Epoch of Galaxy Formation
Motivated by the irregular and little-understood morphologies of z ~ 2 - 3
galaxies, we use non-parametric coefficents to quantify the morphologies of 216
galaxies which have been spectroscopically confirmed to lie at redshifts z =
1.8 - 3.4 in the GOODS-N field. Using measurements of ultraviolet (UV) and
optical spectral lines, multi-band photometric data, and stellar population
models we statistically assess possible correlations between galaxy morphology
and physical observables such as stellar mass, star formation rate, and the
strength of galaxy-scale outflows. We find evidence that dustier galaxies have
more nebulous UV morphologies and that larger, more luminous galaxies may drive
stronger outflows, but otherwise conclude that UV morphology is either
statistically decoupled from the majority of physical observables or determined
by too complex a combination of physical processes to provide characterizations
with predictive power. Given the absence of strong correlations between UV
morphology and physical parameters such as star formation rates, we are
therefore unable to support the hypothesis that morphologically irregular
galaxies predominantly represent major galaxy mergers. Comparing galaxy
samples, we find that IR-selected BzK galaxies and radio-selected submillimeter
galaxies (SMGs) have UV morphologies similar to the optically selected sample,
while distant red galaxies (DRGs) are more nebulous.Comment: 26 pages. Accepted for publication in the ApJ. Version with full
resolution figures is available at
http://www.astro.caltech.edu/~drlaw/Papers/UVmorph.pd
Physical Conditions in a Young, Unreddened, Low Metallicity Galaxy at High Redshift
Increasingly large samples of galaxies are now being discovered at redshifts
z~5-6 and higher. Many of these objects are inferred to be young, low in mass,
and relatively unreddened, but detailed analysis of their high quality spectra
will not be possible until the advent of future facilities. In this paper we
shed light on the physical conditions in a plausibly similar low mass galaxy by
presenting the analysis of the rest-frame optical and UV spectra of
Q2343-BX418, an L* galaxy at z=2.3 with a very low mass-to-light ratio and
unusual properties: BX418 is young (<100 Myr), low mass (M_star ~ 10^9 Msun),
low in metallicity (Z ~ 1/6 Zsun), and unreddened (E(B-V)~0.02, UV continuum
slope beta=-2.1). We infer a metallicity 12+log(O/H)=7.9 +/- 0.2 from the
rest-frame optical emission lines. We also determine the metallicity via the
direct, electron temperature method, using the ratio O III] 1661, 1666/[O III]
5007 to determine the electron temperature and finding 12+ log(O/H)=7.8 +/-
0.1. These measurements place BX418 among the most metal-poor galaxies observed
in emission at high redshift. The rest-frame UV spectrum contains strong
emission from Lya (with rest-frame equivalent width 54 A), He II 1640 (both
stellar and nebular), C III] 1907, 1909 and O III] 1661, 1666. The C IV/C III]
ratio indicates that the source of ionization is unlikely to be an AGN.
Analysis of the He II, O III] and C III] line strengths indicates a very high
ionization parameter log U ~ -1, while Lya and the interstellar absorption
lines indicate that outflowing gas is highly ionized over a wide range of
velocities. It remains to be determined how many of BX418's unique spectral
features are due to its global properties, such as low metallicity and dust
extinction, and how many are indicative of a short-lived phase in the early
evolution of an otherwise normal star-forming galaxy.Comment: Accepted for publication in ApJ. 28 pages, 14 figure
The Gaseous Environment of High-z Galaxies: Precision Measurements of Neutral Hydrogen in the Circumgalactic Medium of z ~ 2-3 Galaxies in the Keck Baryonic Structure Survey
We present results from the Keck Baryonic Structure Survey (KBSS), a unique
spectroscopic survey designed to explore the connection between galaxies and
intergalactic baryons. The KBSS is optimized for the redshift range z ~ 2-3,
combining S/N ~ 100 Keck/HIRES spectra of 15 hyperluminous QSOs with densely
sampled galaxy redshift surveys surrounding each QSO sightline. We perform
Voigt profile decomposition of all 6000 HI absorbers within the full Lya forest
in the QSO spectra. Here we present the distribution, column density,
kinematics, and absorber line widths of HI surrounding 886 star-forming
galaxies with 2.0 < z < 2.8 and within 3 Mpc of a QSO sightline. We find that
N_HI and the multiplicity of HI components increase rapidly near galaxies. The
strongest HI absorbers within ~ 100 physical kpc of galaxies have N_HI ~ 3 dex
higher than those near random locations in the IGM. The circumgalactic zone of
most enhanced HI absorption (CGM) is found within 300 kpc and 300 km/s of
galaxies. Nearly half of absorbers with log(N_HI) > 15.5 are found within the
CGM of galaxies meeting our photometric selection, while their CGM occupy only
1.5% of the cosmic volume. The spatial covering fraction, multiplicity of
absorption components, and characteristic N_HI remain elevated to transverse
distances of 2 physical Mpc. Absorbers with log(N_HI) > 14.5 are tightly
correlated with the positions of galaxies, while absorbers with lower N_HI are
correlated only on Mpc scales. Redshift anisotropies on Mpc scales indicate
coherent infall toward galaxies, while on scales of ~100 physical kpc peculiar
velocities of 260 km/s are indicated. The median Doppler widths of absorbers
within 1-3 virial radii of galaxies are ~50% larger than randomly chosen
absorbers of the same N_HI, suggesting higher gas temperatures and/or increased
turbulence likely caused by accretion shocks and/or galactic winds.Comment: Accepted to Ap
An HST/WFC3-IR Morphological Survey of Galaxies at z = 1.5-3.6: II. The Relation between Morphology and Gas-Phase Kinematics
We analyze rest-frame optical morphologies and gas-phase kinematics as traced
by rest-frame far-UV and optical spectra for a sample of 204 star forming
galaxies in the redshift range z ~ 2-3 drawn from the Keck Baryonic Structure
Survey (KBSS). We find that spectroscopic properties and gas-phase kinematics
are closely linked to morphology: compact galaxies with semi-major axis radii r
<~ 2 kpc are substantially more likely than their larger counterparts to
exhibit LyA in emission. Although LyA emission strength varies widely within
galaxies of a given morphological type, all but one of 19 galaxies with LyA
equivalent width W_LyA > 20 Angstroms have compact and/or multiple-component
morphologies with r <= 2.5 kpc. The velocity structure of absorption lines in
the galactic continuum spectra also varies as a function of morphology.
Galaxies of all morphological types drive similarly strong outflows (as traced
by the blue wing of interstellar absorption line features), but the outflows of
larger galaxies are less highly ionized and exhibit larger optical depth at the
systemic redshift that may correspond to a decreasing efficiency of feedback in
evacuating gas from the galaxy. This v ~ 0 km/s gas is responsible both for
shifting the mean absorption line redshift and attenuating W_LyA (via a longer
resonant scattering path) in galaxies with larger rest-optical half light
radii. In contrast to galaxies at lower redshifts, there is no evidence for a
correlation between outflow velocity and inclination, suggesting that outflows
from these puffy and irregular systems may be poorly collimated. (Abbrev.)Comment: 18 pages, 11 figures. Revised version accepted for publication in
ApJ. Version with full-resolution figures is available at
http://di.utoronto.ca/~drlaw/Papers/wfc3_uvspec.pd
The Kiloparsec-Scale Kinematics of High-Redshift Star-Forming Galaxies
We present the results of a spectroscopic survey of the kinematic structure
of star-forming galaxies at redshift z ~ 2 - 3 using Keck/OSIRIS integral field
spectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0
and 2.5 and one galaxy at z ~ 3.3 which are well detected in either HAlpha or
[O III] emission. These observations were obtained in conjunction with the Keck
laser guide star adaptive optics system, with a typical angular resolution
after spatial smoothing ~ 0.15" (approximately 1 kpc at the redshift of the
target sample). At most five of these 13 galaxies have spatially resolved
velocity gradients consistent with rotation while the remaining galaxies have
relatively featureless or irregular velocity fields. All of our galaxies show
local velocity dispersions ~ 60 - 100 km/s, suggesting that (particularly for
those galaxies with featureless velocity fields) rotation about a preferred
axis may not be the dominant mechanism of physical support. While some galaxies
show evidence for major mergers such evidence is unrelated to the kinematics of
individual components (one of our strongest merger candidates also exhibits
unambiguous rotational structure), refuting a simple bimodal disk/merger
classification scheme. We discuss these data in light of complementary surveys
and extant UV-IR spectroscopy and photometry, concluding that the dynamical
importance of cold gas may be the primary factor governing the observed
kinematics of z ~ 2 galaxies. We conclude by speculating on the importance of
mechanisms for accreting low angular-momentum gas and the early formation of
quasi-spheroidal systems in the young universe.(abridged)Comment: 34 pages, 13 figures. Revised version accepted for publication in the
Astrophysical Journal. Version with full-resolution figures is available at
http://www.astro.ucla.edu/~drlaw/Papers/OSIRIS_data2.pd
Control of the Scattering Properties of Complex Systems By Means of Tunable Metasurfaces
We demonstrate the ability to control the scattering properties of a
two-dimensional wave-chaotic microwave billiard through the use of tunable
metasurfaces located on the interior walls of the billiard. The complex
reflection coefficient of the metasurfaces can be varied by applying a DC
voltage bias to varactor diodes on mushroom-shaped resonant patches, and this
proves to be very effective at perturbing the eigenmodes of the cavity. Placing
multiple metasurfaces inside the cavity allows us to engineer desired
scattering conditions, such as coherent perfect absorption (CPA), by actively
manipulating the poles and zeros of the scattering matrix through the
application of multiple voltage biases. We demonstrate the ability to create
on-demand CPA conditions at a specific frequency, and document the near-null of
output power as a function of four independent parameters tuned through the CPA
point. A remarkably low output-to-input power ratio of is achieved near the CPA point at 8.54 GHz
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