2,689 research outputs found
Degradation of a quantum reference frame
We investigate the degradation of reference frames, treated as dynamical
quantum systems, and quantify their longevity as a resource for performing
tasks in quantum information processing. We adopt an operational measure of a
reference frame's longevity, namely, the number of measurements that can be
made against it with a certain error tolerance. We investigate two distinct
types of reference frame: a reference direction, realized by a spin-j system,
and a phase reference, realized by an oscillator mode with bounded energy. For
both cases, we show that our measure of longevity increases quadratically with
the size of the reference system and is therefore non-additive. For instance,
the number of measurements that a directional reference frame consisting of N
parallel spins can be put to use scales as N^2. Our results quantify the extent
to which microscopic or mesoscopic reference frames may be used for repeated,
high-precision measurements, without needing to be reset - a question that is
important for some implementations of quantum computing. We illustrate our
results using the proposed single-spin measurement scheme of magnetic resonance
force microscopy.Comment: 9 pages plus appendices, 4 figures, published versio
Reversible positioning of single molecules inside zero-mode waveguides
We have developed a hybrid nanopore/zero-mode waveguide device for single-molecule fluorescence and DNA sequencing applications. The device is a freestanding solid-state membrane with sub-5 nm nanopores that reversibly delivers individual biomolecules to the base of 70 nm diameter waveguides for interrogation. Rapid and reversible molecular loading is achieved by controlling the voltage across the device. Using this device we demonstrate protein and DNA loading with efficiency that is orders of magnitude higher than diffusion-based molecular loading.R21 HG006873 - NHGRI NIH HHS; R21-HG006873 - NHGRI NIH HHSPublished versio
Live-Cell Imaging of Single Receptor Composition Using Zero-Mode Waveguide Nanostructures
We exploit the optical and spatial features of subwavelength nanostructures to examine individual receptors on the plasma membrane of living cells. Receptors were sequestered in portions of the membrane projected into zero-mode waveguides. Using single-step photobleaching of green fluorescent protein incorporated into individual subunits, the resulting spatial isolation was used to measure subunit stoichiometry in α4β4 and α4β2 nicotinic acetylcholine and P2X2 ATP receptors. We also show that nicotine and cytisine have differential effects on α4β2 stoichiometry
Direct Detection and Sequencing of Damaged DNA Bases
Products of various forms of DNA damage have been implicated in a variety of important biological processes, such as aging, neurodegenerative diseases, and cancer. Therefore, there exists great interest to develop methods for interrogating damaged DNA in the context of sequencing. Here, we demonstrate that single-molecule, real-time (SMRT®) DNA sequencing can directly detect damaged DNA bases in the DNA template - as a by-product of the sequencing method - through an analysis of the DNA polymerase kinetics that are altered by the presence of a modified base. We demonstrate the sequencing of several DNA templates containing products of DNA damage, including 8-oxoguanine, 8-oxoadenine, O6-methylguanine, 1-methyladenine, O4-methylthymine, 5-hydroxycytosine, 5-hydroxyuracil, 5-hydroxymethyluracil, or thymine dimers, and show that these base modifications can be readily detected with single-modification resolution and DNA strand specificity. We characterize the distinct kinetic signatures generated by these DNA base modifications
Autocatalytic plume pinch-off
A localized source of buoyancy flux in a non-reactive fluid medium creates a
plume. The flux can be provided by either heat, a compositional difference
between the fluid comprising the plume and its surroundings, or a combination
of both. For autocatalytic plumes produced by the iodate-arsenous acid
reaction, however, buoyancy is produced along the entire reacting interface
between the plume and its surroundings. Buoyancy production at the moving
interface drives fluid motion, which in turn generates flow that advects the
reaction front. As a consequence of this interplay between fluid flow and
chemical reaction, autocatalytic plumes exhibit a rich dynamics during their
ascent through the reactant medium. One of the more interesting dynamical
features is the production of an accelerating vortical plume head that in
certain cases pinches-off and detaches from the upwelling conduit. After
pinch-off, a new plume head forms in the conduit below, and this can lead to
multiple generations of plume heads for a single plume initiation. We
investigated the pinch-off process using both experimentation and simulation.
Experiments were performed using various concentrations of glycerol, in which
it was found that repeated pinch-off occurs exclusively in a specific
concentration range. Autocatalytic plume simulations revealed that pinch-off is
triggered by the appearance of accelerating flow in the plume conduit.Comment: 10 figures. Accepted for publication in Phys Rev E. See also
http://www.physics.utoronto.ca/nonlinear/papers_chemwave.htm
Natural versus forced convection in laminar starting plumes
A starting plume or jet has a well-defined, evolving head that is driven
through the surrounding quiescent fluid by a localized flux of either buoyancy
or momentum, or both. We studied the scaling and morphology of starting plumes
produced by a constant flux of buoyant fluid from a small, submerged outlet.
The plumes were laminar and spanned a wide range of plume Richardson numbers
Ri. Ri is the dimensionless ratio of the buoyancy forces to inertial effects,
and is thus our measurements crossed over the transition between
buoyancy-driven plumes and momentum-driven jets. We found that the ascent
velocity of the plume, nondimensionalized by Ri, exhibits a power law
relationship with Re, the Reynolds number of the injected fluid in the outlet
pipe. We also found that as the threshold between buoyancy-driven and
momentum-driven flow was crossed, two distinct types of plume head mophologies
existed: confined heads, produced in the Ri > 1 regime, and dispersed heads,
which are found in the Ri < 1 regime. Head dispersal is caused by a breakdown
of overturning motion in the head, and a local Kelvin-Helmholtz instability on
the exterior of the plume.Comment: 8 pages, 8 figures, accepted for publication in Physics of Fluids
(final version with corrections
Old Black Joe / music by J. W. Turner; words by Stephen Foster
Cover: Fosters Original Theme, with New and Sparkling Variations; Publisher: Hitchcock and McCargo Publishing Co. (New York)https://egrove.olemiss.edu/sharris_a/1019/thumbnail.jp
Chain Galaxies are Edge-On Low Surface Brightness Galaxies
Deep HST WFPC2 images have revealed a population of very narrow blue galaxies
which Cowie et al. (1996) have interpreted as being a new morphological class
of intrinsically linear star forming galaxies at . We show that the
same population exists in large numbers at low redshifts (z=0.03) and are
actually the edge-on manifestation of low surface brightness disk galaxies.Comment: 18 pages + 3 pages of figures. Uuencoded, gzipped, tar file of 1
latex file, 5 figures, and 2 latex style files. To appear in the
Astrophysical Journal Letter
Quantum communication using a bounded-size quantum reference frame
Typical quantum communication schemes are such that to achieve perfect
decoding the receiver must share a reference frame with the sender. Indeed, if
the receiver only possesses a bounded-size quantum token of the sender's
reference frame, then the decoding is imperfect, and we can describe this
effect as a noisy quantum channel. We seek here to characterize the performance
of such schemes, or equivalently, to determine the effective decoherence
induced by having a bounded-size reference frame. We assume that the token is
prepared in a special state that has particularly nice group-theoretic
properties and that is near-optimal for transmitting information about the
sender's frame. We present a decoding operation, which can be proven to be
near-optimal in this case, and we demonstrate that there are two distinct ways
of implementing it (corresponding to two distinct Kraus decompositions). In
one, the receiver measures the orientation of the reference frame token and
reorients the system appropriately. In the other, the receiver extracts the
encoded information from the virtual subsystems that describe the relational
degrees of freedom of the system and token. Finally, we provide explicit
characterizations of these decoding schemes when the system is a single qubit
and for three standard kinds of reference frame: a phase reference, a Cartesian
frame (representing an orthogonal triad of spatial directions), and a reference
direction (representing a single spatial direction).Comment: 17 pages, 1 figure, comments welcome; v2 published versio
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