14,955 research outputs found
THERMTRAJ: A FORTRAN program to compute the trajectory and gas film temperatures of zero pressure balloons
A FORTRAN computer program called THERMTRAJ is presented which can be used to compute the trajectory of high altitude scientific zero pressure balloons from launch through all subsequent phases of the balloon flight. In addition, balloon gas and film temperatures can be computed at every point of the flight. The program has the ability to account for ballasting, changes in cloud cover, variable atmospheric temperature profiles, and both unconditional valving and scheduled valving of the balloon gas. The program was verified for an extensive range of balloon sizes (from 0.5 to 41.47 million cubic feet). Instructions on program usage, listing of the program source deck, input data and printed and plotted output for a verification case are included
A unified thermal and vertical trajectory model for the prediction of high altitude balloon performance
A computer model for the prediction of the trajectory and thermal behavior of zero-pressure high altitude balloon was developed. In accord with flight data, the model permits radiative emission and absorption of the lifting gas and daytime gas temperatures above that of the balloon film. It also includes ballasting, venting, and valving. Predictions obtained with the model are compared with flight data from several flights and newly discovered features are discussed
Squeezing as an irreducible resource
We show that squeezing is an irreducible resource which remains invariant
under transformations by linear optical elements. In particular, we give a
decomposition of any optical circuit with linear input-output relations into a
linear multiport interferometer followed by a unique set of single mode
squeezers and then another multiport interferometer. Using this decomposition
we derive a no-go theorem for superpositions of macroscopically distinct states
from single-photon detection. Further, we demonstrate the equivalence between
several schemes for randomly creating polarization-entangled states. Finally,
we derive minimal quantum optical circuits for ideal quantum non-demolition
coupling of quadrature-phase amplitudes.Comment: 4 pages, 3 figures, new title, removed the fat
Electrostatic Contributions of Aromatic Residues in the Local Anesthetic Receptor of Voltage-Gated Sodium Channels
Antiarrhythmics, anticonvulsants, and local anesthetics target voltage-gated sodium channels, decreasing excitability of nerve and muscle cells. Channel inhibition by members of this family of cationic, hydrophobic drugs relies on the presence of highly conserved aromatic residues in the pore-lining S6 segment of the fourth homologous domain of the channel. We tested whether channel inhibition was facilitated by an electrostatic attraction between lidocaine and {pi} electrons of the aromatic rings of these residues, namely a cation-{pi} interaction. To this end, we used the in vivo nonsense suppression method to incorporate a series of unnatural phenylalanine derivatives designed to systematically reduce the negative electrostatic potential on the face of the aromatic ring. In contrast to standard point mutations at the same sites, these subtly altered amino acids preserve the wild-type voltage dependence of channel activation and inactivation. Although these phenylalanine derivatives have no effect on low-affinity tonic inhibition by lidocaine or its permanently charged derivative QX-314 at any of the substituted sites, high-affinity use-dependent inhibition displays substantial cation-{pi} energetics for 1 residue only: Phe1579 in rNaV1.4. Replacement of the aromatic ring of Phe1579 by cyclohexane, for example, strongly reduces use-dependent inhibition and speeds recovery of lidocaine-engaged channels. Channel block by the neutral local anesthetic benzocaine is unaffected by the distribution of {pi} electrons at Phe1579, indicating that our aromatic manipulations expose electrostatic contributions to channel inhibition. These results fine tune our understanding of local anesthetic inhibition of voltage-gated sodium channels and will help the design of safer and more salutary therapeutic agents
Superfluid to normal phase transition in strongly correlated bosons in two and three dimensions
Using quantum Monte Carlo simulations, we investigate the finite-temperature
phase diagram of hard-core bosons (XY model) in two- and three-dimensional
lattices. To determine the phase boundaries, we perform a finite-size-scaling
analysis of the condensate fraction and/or the superfluid stiffness. We then
discuss how these phase diagrams can be measured in experiments with trapped
ultracold gases, where the systems are inhomogeneous. For that, we introduce a
method based on the measurement of the zero-momentum occupation, which is
adequate for experiments dealing with both homogeneous and trapped systems, and
compare it with previously proposed approaches.Comment: 13 pages, 11 figures.
http://link.aps.org/doi/10.1103/PhysRevA.86.04362
A Cation–π Interaction between Extracellular TEA and an Aromatic Residue in Potassium Channels
Open-channel blockers such as tetraethylammonium (TEA) have a long history as probes of the permeation pathway of ion channels. High affinity blockade by extracellular TEA requires the presence of an aromatic amino acid at a position that sits at the external entrance of the permeation pathway (residue 449 in the eukaryotic voltage-gated potassium channel Shaker). We investigated whether a cation–{pi} interaction between TEA and such an aromatic residue contributes to TEA block using the in vivo nonsense suppression method to incorporate a series of increasingly fluorinated Phe side chains at position 449. Fluorination, which is known to decrease the cation–{pi} binding ability of an aromatic ring, progressively increased the inhibitory constant Ki for the TEA block of Shaker. A larger increase in Ki was observed when the benzene ring of Phe449 was substituted by nonaromatic cyclohexane. These results support a strong cation–{pi} component to the TEA block. The data provide an empirical basis for choosing between Shaker models that are based on two classes of reported crystal structures for the bacterial channel KcsA, showing residue Tyr82 in orientations either compatible or incompatible with a cation–{pi} mechanism. We propose that the aromatic residue at this position in Shaker is favorably oriented for a cation–{pi} interaction with the permeation pathway. This choice is supported by high level ab initio calculations of the predicted effects of Phe modifications on TEA binding energy
Spectral Conditions on the State of a Composite Quantum System Implying its Separability
For any unitarily invariant convex function F on the states of a composite
quantum system which isolates the trace there is a critical constant C such
that F(w)<= C for a state w implies that w is not entangled; and for any
possible D > C there are entangled states v with F(v)=D. Upper- and lower
bounds on C are given. The critical values of some F's for qubit/qubit and
qubit/qutrit bipartite systems are computed. Simple conditions on the spectrum
of a state guaranteeing separability are obtained. It is shown that the thermal
equilbrium states specified by any Hamiltonian of an arbitrary compositum are
separable if the temperature is high enough.Comment: Corrects 1. of Lemma 2, and the (under)statement of Proposition 7 of
the earlier version
Entanglement-Saving Channels
The set of Entanglement Saving (ES) quantum channels is introduced and
characterized. These are completely positive, trace preserving transformations
which when acting locally on a bipartite quantum system initially prepared into
a maximally entangled configuration, preserve its entanglement even when
applied an arbitrary number of times. In other words, a quantum channel
is said to be ES if its powers are not entanglement-breaking for all
integers . We also characterize the properties of the Asymptotic
Entanglement Saving (AES) maps. These form a proper subset of the ES channels
that is constituted by those maps which, not only preserve entanglement for all
finite , but which also sustain an explicitly not null level of entanglement
in the asymptotic limit~. Structure theorems are provided
for ES and for AES maps which yield an almost complete characterization of the
former and a full characterization of the latter.Comment: 26 page
Optimal state encoding for quantum walks and quantum communication over spin systems
Recent work has shown that a simple chain of interacting spins can be used as
a medium for high-fidelity quantum communication. We describe a scheme for
quantum communication using a spin system that conserves z-spin, but otherwise
is arbitrary. The sender and receiver are assumed to directly control several
spins each, with the sender encoding the message state onto the larger
state-space of her control spins. We show how to find the encoding that
maximises the fidelity of communication, using a simple method based on the
singular-value decomposition. Also, we show that this solution can be used to
increase communication fidelity in a rather different circumstance: where no
encoding of initial states is used, but where the sender and receiver control
exactly two spins each and vary the interactions on those spins over time. The
methods presented are computationally efficient, and numerical examples are
given for systems having up to 300 spins.Comment: 10 pages, LaTeX, 7 EPS figures. Corrected an error in the definition
and interpretation of C_B(T
Discrimination between evolution operators
Under broad conditions, evolutions due to two different Hamiltonians are
shown to lead at some moment to orthogonal states. For two spin-1/2 systems
subject to precession by different magnetic fields the achievement of
orthogonalization is demonstrated for every scenario but a special one. This
discrimination between evolutions is experimentally much simpler than
procedures proposed earlier based on either sequential or parallel application
of the unknown unitaries. A lower bound for the orthogonalization time is
proposed in terms of the properties of the two Hamiltonians.Comment: 7 pages, 2 figures, REVTe
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