65,949 research outputs found
Sustained magneto-shear instabilities in the solar tachocline
We present nonlinear three-dimensional simulations of the stably-stratified
portion of the solar tachocline in which the rotational shear is maintained by
mechanical forcing. When a broad toroidal field profile is specified as an
initial condition, a clam-shell instability ensues which is similar to the
freely-evolving cases studied previously. After the initial nonlinear
saturation, the residual mean fields are apparently too weak to sustain the
instability indefinitely. However, when a mean poloidal field is imposed in
addition to the rotational shear, a statistically-steady state is achieved in
which the clam-shell instability is operating continually. This state is
characterized by a quasi-periodic exchange of energy between the mean toroidal
field and the instability mode with a longitudinal wavenumber m=1. This
quasi-periodic behavior has a timescale of several years and may have
implications for tachocline dynamics and field emergence patterns throughout
the solar activity cycle.Comment: 5 pages, 3 figures (eps format). Fig. 3 also in jpg format. Submitted
to Astrophysical Journal Letter
DO SPORTFISH CONSUMPTION ADVISORIES AFFECT RESERVOIR ANGLERS' SITE CHOICE?
Increasing numbers of freshwater ecosystems have had sportfish consumption advisories posted in recent years. Advisories are sometimes issued in lieu of environmental remediation if they are considered more cost-effective than "cleaning up" the resource, but this approach assumes that anglers adjust behavior in response to the warning. Previous studies, however, suggest that compliance with advisories can be quite low. In contrast, this study measures a statistically significant response by reservoir anglers to consumption advisories. In particular, anglers are less likely to choose to visit a reservoir with an advisory than a similar reservoir without an advisory. Furthermore, the economic losses due to advisories are quantified for anglers in two regions of Tennessee.Resource /Energy Economics and Policy,
Multiphoton resonances for all-optical quantum logic with multiple cavities
We develop a theory for the interaction of multilevel atoms with multimode cavities yielding cavity-enhanced multiphoton resonances. The locations of the resonances are predicted from the use of effective two- and three-level Hamiltonians. As an application we show that quantum gates can be realized when photonic qubits are encoded on the cavity modes in arrangements where ancilla atoms transit the cavity. The fidelity of operations is increased by conditional measurements on the atom and by the use of a selected, dual-rail, Hilbert space. A universal set of gates is proposed, including the Fredkin gate and iSWAP operation; the system seems promising for scalability
The Terwilliger algebra of an almost-bipartite P- and Q-polynomial association scheme
Let denote a -class symmetric association scheme with , and
suppose is almost-bipartite P- and Q-polynomial. Let denote a vertex of
and let denote the corresponding Terwilliger algebra. We prove
that any irreducible -module is both thin and dual thin in the sense of
Terwilliger. We produce two bases for and describe the action of on
these bases. We prove that the isomorphism class of as a -module is
determined by two parameters, the dual endpoint and diameter of . We find a
recurrence which gives the multiplicities with which the irreducible
-modules occur in the standard module. We compute this multiplicity for
those irreducible -modules which have diameter at least .Comment: 22 page
Hybrid stars that masquerade as neutron stars
We show that a hybrid (nuclear + quark matter) star can have a mass-radius
relationship very similar to that predicted for a star made of purely nucleonic
matter. We show this for a generic parameterization of the quark matter
equation of state, and also for an MIT bag model, each including a
phenomenological correction based on gluonic corrections to the equation of
state. We obtain hybrid stars as heavy as 2 M_solar for reasonable values of
the bag model parameters. For nuclear matter, we use the equation of state
calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques.
Both mixed and homogeneous phases of nuclear and quark matter are considered.Comment: 22 pages, LaTeX. Extra figure and explanation adde
Virus-transformed pre-B cells show ordered activation but not inactivation of immunoglobulin gene rearrangement and transcription
Virus-transformed pre-B cells undergo ordered immunoglobulin (Ig) gene rearrangements during culture. We devised a series of highly sensitive polymerase chain reaction assays for Ig gene rearrangement and unrearranged Ig gene segment transcription to study both the possible relationship between these processes in cultured pre-B cells and the role played by heavy (H) chain (mu) protein in regulating gene rearrangement. Our analysis of pre-B cell cultures representing various stages of maturity revealed that transcription of each germline Ig locus precedes or is coincident with its rearrangement. Cell lines containing one functional rearranged H chain allele, however, continue to transcribe and to rearrange the allelic, unrearranged H chain locus. These cell lines appear to initiate but not terminate rearrangement events and therefore provide information about the requirements for activating rearrangement but not about allelic exclusion mechanisms
Quantum Channel Capacities Per Unit Cost
Communication over a noisy channel is often conducted in a setting in which
different input symbols to the channel incur a certain cost. For example, for
bosonic quantum channels, the cost associated with an input state is the number
of photons, which is proportional to the energy consumed. In such a setting, it
is often useful to know the maximum amount of information that can be reliably
transmitted per cost incurred. This is known as the capacity per unit cost. In
this paper, we generalize the capacity per unit cost to various communication
tasks involving a quantum channel such as classical communication,
entanglement-assisted classical communication, private communication, and
quantum communication. For each task, we define the corresponding capacity per
unit cost and derive a formula for it analogous to that of the usual capacity.
Furthermore, for the special and natural case in which there is a zero-cost
state, we obtain expressions in terms of an optimized relative entropy
involving the zero-cost state. For each communication task, we construct an
explicit pulse-position-modulation coding scheme that achieves the capacity per
unit cost. Finally, we compute capacities per unit cost for various bosonic
Gaussian channels and introduce the notion of a blocklength constraint as a
proposed solution to the long-standing issue of infinite capacities per unit
cost. This motivates the idea of a blocklength-cost duality, on which we
elaborate in depth.Comment: v3: 18 pages, 2 figure
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