271 research outputs found
Quantitative acoustic models for superfluid circuits
We experimentally realize a highly tunable superfluid oscillator circuit in a
quantum gas of ultracold atoms and develop and verify a simple lumped-element
description of this circuit. At low oscillator currents, we demonstrate that
the circuit is accurately described as a Helmholtz resonator, a fundamental
element of acoustic circuits. At larger currents, the breakdown of the
Helmholtz regime is heralded by a turbulent shedding of vortices and density
waves. Although a simple phase-slip model offers qualitative insights into the
circuit's resistive behavior, our results indicate deviations from the
phase-slip model. A full understanding of the dissipation in superfluid
circuits will thus require the development of empirical models of the turbulent
dynamics in this system, as have been developed for classical acoustic systems.Comment: 12 pages, 9 figure
Monocyte surface expression of FcÎł receptor RI (CD64), a biomarker reflecting type-I interferon levels in systemic lupus erythematosus
Coherent vortex dynamics in a strongly-interacting superfluid on a silicon chip
Two-dimensional superfluidity and quantum turbulence are directly connected
to the microscopic dynamics of quantized vortices. However, surface effects
have prevented direct observations of coherent vortex dynamics in
strongly-interacting two-dimensional systems. Here, we overcome this challenge
by confining a two-dimensional droplet of superfluid helium at microscale on
the atomically-smooth surface of a silicon chip. An on-chip optical microcavity
allows laser-initiation of vortex clusters and nondestructive observation of
their decay in a single shot. Coherent dynamics dominate, with thermal vortex
diffusion suppressed by six orders-of-magnitude. This establishes a new on-chip
platform to study emergent phenomena in strongly-interacting superfluids, test
astrophysical dynamics such as those in the superfluid core of neutron stars in
the laboratory, and construct quantum technologies such as precision inertial
sensors.Comment: Main text - 12 pages, 4 figures. Supplementary materials - 25 pages,
13 figure
Emergence of off-axis equilibria in a quantum vortex gas
We experimentally study the emergence of high-energy equilibrium states in a
chiral vortex gas of like-circulation vortices realized within a disk-shaped
atomic Bose-Einstein condensate. In contrast to the familiar triangular
Abrikosov lattice, the lowest-energy state of the superfluid in a rotating
frame, we observe the formation of rotating vortex equilibria that are highly
disordered and have significant energy per vortex. Experimental stirring
protocols realize equilibrium states at both positive and negative absolute
temperatures of the vortex gas. At sufficiently high energies the system
exhibits a symmetry breaking transition, resulting in an off-axis equilibrium
phase that no longer shares the symmetry of the container. By initializing
vortices in a non-equilibrium distribution with sufficient energy, relaxation
to equilibrium is observed within experimental timescales and an off-axis
equilibrium state emerges at negative absolute temperature. The observed
equilibria are in close agreement with mean field theory of the microcanonical
ensemble of the vortex gas.Comment: V1: 13 pages, 6 figures, 5 in main tex
Trends and emissions of six perfluorocarbons in the Northern Hemisphere and Southern Hemisphere
Perfluorocarbons (PFCs) are potent greenhouse gases with global warming potentials up to several thousand times greater than CO2 on a 100-year time horizon. The lack of any significant sinks for PFCs means that they have long atmospheric lifetimes of the order of thousands of years. Anthropogenic production is thought to be the only source for most PFCs. Here we report an update on the global atmospheric abundances of the following PFCs, most of which have for the first time been analytically separated according to their isomers: c-octafluorobutane (c-C4F8), n-decafluorobutane (n-C4F10), n-dodecafluoropentane (n-C5F12), n-tetradecafluorohexane (n-C6F14), and n-hexadecafluoroheptane (n-C7F16). Additionally, we report the first data set on the atmospheric mixing ratios of perfluoro-2-methylpentane (i-C6F14). The existence and significance of PFC isomers have not been reported before, due to the analytical challenges of separating them. The time series spans a period from 1978 to the present. Several data sets are used to investigate temporal and spatial trends of these PFCs: time series of air samples collected at Cape Grim, Australia, from 1978 to the start of 2018; a time series of air samples collected between July 2015 and April 2017 at Tacolneston, UK; and intensive campaign-based sampling collections from Taiwan. Although the remote “background” Southern Hemispheric Cape Grim time series indicates that recent growth rates of most of these PFCs are lower than in the 1990s, we continue to see significantly increasing mixing ratios that are between 6 % and 27 % higher by the end of 2017 compared to abundances measured in 2010. Air samples from Tacolneston show a positive offset in PFC mixing ratios compared to the Southern Hemisphere baseline. The highest mixing ratios and variability are seen in air samples from Taiwan, which is therefore likely situated much closer to PFC sources, confirming predominantly Northern Hemispheric emissions for most PFCs. Even though these PFCs occur in the atmosphere at levels of parts per trillion molar or less, their total cumulative global emissions translate into 833 million metric tonnes of CO2 equivalent by the end of 2017, 23 % of which has been emitted since 2010. Almost two-thirds of the CO2 equivalent emissions within the last decade are attributable to c-C4F8, which currently also has the highest emission rates that continue to grow. Sources of all PFCs covered in this work remain poorly constrained and reported emissions in global databases do not account for the abundances found in the atmosphere
Epitope-specific humoral responses to human cytomegalovirus glycoprotein-B vaccine with MF59: Anti-AD2 levels correlate with protection from viremia
The human cytomegalovirus (HCMV) virion envelope protein glycoprotein B (gB) is essential for viral entry and represents a major target for humoral responses following infection. Previously, a phase-2 placebo-controlled clinical trial conducted in solid organ transplant candidates demonstrated that vaccination with gB plus MF59 adjuvant significantly increased gB ELISA antibody levels whose titer correlated directly with protection against post-transplant viremia. The aim of the current study was to investigate in more detail this protective humoral response in vaccinated seropositive transplant recipients. We focussed on four key antigenic domains (AD) of gB; AD1, AD2, AD4 and AD5 measuring antibody levels in patient sera and correlating these with post-transplant HCMV viremia. Vaccination of seropositive patients significantly boosted pre-existing antibody levels against the immunodominant region AD1 as well as against AD2, AD4 and AD5. A decreased incidence of viremia correlated with higher antibody titers against AD2 but not with antibody titers against the other three ADs. Overall, these data support the hypothesis that antibodies against AD2 are a major component of the immune protection of seropositives seen following vaccination with gB/MF59 vaccine and identify a correlate of protective immunity in allograft patients
Understory 2014
“Art is the struggle to be, in a particular sort
of way, virtuous.” —Iris Murdoch
Indeed, when we embark on any creative adventure
it is with the purpose of conveying a certain truth; an
emotion, an idea that brings us together and reminds us
of the innate consciousness that dwells within.
Understory is emblematic of this; where individuals
intent on honing their craft can join others to become a
part of something greater, their work immortalized to
become a time capsule. Decades from now a volume of
Understory may be discovered on a dusty bookshelf in
some forgotten corner and the lucky explorer who finds it
shall be enlightened by pages of gold.
We, as editors of Understory 2014, have worked
very hard this year to put together a journal that showcases
the very best of the University of Alaska Anchorage
undergraduate student work. We hope you enjoy your
journey through this issue as much as we have enjoyed ours.
Thank you to the English and Art Departments,
for the staff and faculty’s unerring support of our club;
to Provost Baker, for seeing and believing in the vision
of Understory; and to our club’s faculty advisor, Douglass
Bourne, for his guidance and tireless assistance. Finally,
thank you to the wonderful students who submit such
excellent work each year. Without your passion for the
arts, we would not be here.Staff / Letter from the Editors / Glass Blower / Writing / Obsolete Evolution / Permafrost / Phoenix / Untitled / Ratio / Tripping / Abiogenesis / My Heart Beats for You / Meeting of the Fingerprint Lines / You Are No Stranger / Nightmare Fuel / Cane-Sugar / Gossamer Strands / Panthera Gold / Butterfly / A Mantis Too Far / Long and Winding Road / Chasing Shadows / Merisunas / Chequer Grove / Modzilla / Beans / Little Red and Mr. Wolf / In Memoriam, Joel Fletcher Armstrong / Glance / Courage / Uranium Waltz / Danger / Journey to the West / Antumbra / Roaring Like a Lion / Pre-boarding / Untitled / How Do You Say a Word / Fishing for Doom/ Contributor
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