268 research outputs found
Quantum Computation as Geometry
Quantum computers hold great promise, but it remains a challenge to find
efficient quantum circuits that solve interesting computational problems. We
show that finding optimal quantum circuits is essentially equivalent to finding
the shortest path between two points in a certain curved geometry. By recasting
the problem of finding quantum circuits as a geometric problem, we open up the
possibility of using the mathematical techniques of Riemannian geometry to
suggest new quantum algorithms, or to prove limitations on the power of quantum
computers.Comment: 13 Pages, 1 Figur
Endogenous lysophosphatidic acid (LPA1) receptor agonists demonstrate ligand bias between calcium and ERK signalling pathways in human lung fibroblasts
Background and Purpose
Human lung fibroblasts (HLF) express high levels of the LPA1 receptor, a GPCR that responds to the endogenous lipid mediator, lysophosphatidic acid (LPA). Several molecular species or analogues of LPA exist and have been detected in biological fluids such as serum and plasma. The most widely expressed of the LPA receptor family is the LPA1 receptor, which predominantly couples to Gq/11, Gi/o and G12/13 proteins. This promiscuity of coupling raises the possibility that some of the LPA analogues may bias the LPA1 receptor towards one signalling pathway over another.
Experimental Approach
Here, we have explored the signalling profiles of a range of LPA analogues in HLF that endogenously express the LPA1 receptor. HLF were treated with LPA analogues and receptor activation monitored via calcium mobilization and ERK phosphorylation.
Key Results
These analyses demonstrated that the 16:0, 17:0, 18:2 and C18:1 LPA analogues appear to exhibit ligand bias between ERK phosphorylation and calcium mobilization when compared with 18:1 LPA, one of the most abundant forms of LPA that has been found in human plasma.
Conclusion and Implications
The importance of LPA as a key signalling molecule is shown by its widespread occurrence in biological fluids and its association with disease conditions such as fibrosis and cancer. These findings have important, as yet unexplored, implications for the (patho-) physiological signalling of the LPA1 receptor, as it may be influenced not only by the concentration of endogenous ligand but the isoform as well
Entanglement of indistinguishable particles in condensed matter physics
The concept of entanglement in systems where the particles are
indistinguishable has been the subject of much recent interest and controversy.
In this paper we study the notion of entanglement of particles introduced by
Wiseman and Vaccaro [Phys. Rev. Lett. 91, 097902 (2003)] in several specific
physical systems, including some that occur in condensed matter physics. The
entanglement of particles is relevant when the identical particles are
itinerant and so not distinguished by their position as in spin models. We show
that entanglement of particles can behave differently to other approaches that
have been used previously, such as entanglement of modes (occupation-number
entanglement) and the entanglement in the two-spin reduced density matrix. We
argue that the entanglement of particles is what could actually be measured in
most experimental scenarios and thus its physical significance is clear. This
suggests entanglement of particles may be useful in connecting theoretical and
experimental studies of entanglement in condensed matter systems.Comment: 13 pages, 6 figures, comments welcome, published version (minor
changes, added references
Selective inhibition of histamine-evoked Ca2+ signals by compartmentalized cAMP in human bronchial airway smooth muscle cells.
Intracellular Ca2+ and cAMP typically cause opposing effects on airway smooth muscle contraction. Receptors that stimulate these pathways are therapeutic targets in asthma and chronic obstructive pulmonary disease. However, the interactions between different G protein-coupled receptors (GPCRs) that evoke cAMP and Ca2+ signals in human bronchial airway smooth muscle cells (hBASMCs) are poorly understood. We measured Ca2+ signals in cultures of fluo-4-loaded hBASMCs alongside measurements of intracellular cAMP using mass spectrometry or [3H]-adenine labeling. Interactions between the signaling pathways were examined using selective ligands of GPCRs, and inhibitors of Ca2+ and cAMP signaling pathways. Histamine stimulated Ca2+ release through inositol 1,4,5-trisphosphate (IP3) receptors in hBASMCs. ÎČ2-adrenoceptors, through cAMP and protein kinase A (PKA), substantially inhibited histamine-evoked Ca2+ signals. Responses to other Ca2+-mobilizing stimuli were unaffected by cAMP (carbachol and bradykinin) or minimally affected (lysophosphatidic acid). Prostaglandin E2 (PGE2), through EP2 and EP4 receptors, stimulated formation of cAMP and inhibited histamine-evoked Ca2+ signals. There was no consistent relationship between the inhibition of Ca2+ signals and the amounts of intracellular cAMP produced by different stimuli. We conclude that ÎČ-adrenoceptors, EP2 and EP4 receptors, through cAMP and PKA, selectively inhibit Ca2+ signals evoked by histamine in hBASMCs, suggesting that PKA inhibits an early step in H1 receptor signaling. Local delivery of cAMP within hyperactive signaling junctions mediates the inhibition
The time-reversal test for stochastic quantum dynamics
The calculation of quantum dynamics is currently a central issue in
theoretical physics, with diverse applications ranging from ultra-cold atomic
Bose-Einstein condensates (BEC) to condensed matter, biology, and even
astrophysics. Here we demonstrate a conceptually simple method of determining
the regime of validity of stochastic simulations of unitary quantum dynamics by
employing a time-reversal test. We apply this test to a simulation of the
evolution of a quantum anharmonic oscillator with up to
(Avogadro's number) of particles. This system is realisable as a Bose-Einstein
condensate in an optical lattice, for which the time-reversal procedure could
be implemented experimentally.Comment: revtex4, two figures, four page
Optimal control, geometry, and quantum computing
We prove upper and lower bounds relating the quantum gate complexity of a
unitary operation, U, to the optimal control cost associated to the synthesis
of U. These bounds apply for any optimal control problem, and can be used to
show that the quantum gate complexity is essentially equivalent to the optimal
control cost for a wide range of problems, including time-optimal control and
finding minimal distances on certain Riemannian, subriemannian, and Finslerian
manifolds. These results generalize the results of Nielsen, Dowling, Gu, and
Doherty, Science 311, 1133-1135 (2006), which showed that the gate complexity
can be related to distances on a Riemannian manifoldComment: 7 Pages Added Full Names to Author
The pharmacological rationale for combining muscarinic receptor antagonists and beta-adrenoceptor agonists in the treatment of airway and bladder disease
Muscarinic receptor antagonists and beta-adrenoceptor agonists are used in the treatment of obstructive airway disease and overactive bladder syndrome. Here we review the pharmacological rationale for their combination. Muscarinic receptors and beta-adrenoceptors are physiological antagonists for smooth muscle tone in airways and bladder. Muscarinic agonism may attenuate beta-adrenoceptor-mediated relaxation more than other contractile stimuli. Chronic treatment with one drug class may regulate expression of the target receptor but also that of the opposing receptor. Prejunctional beta(2)-adrenoceptors can enhance neuronal acetylcholine release. Moreover, at least in the airways, muscarinic receptors and beta-adrenoceptors are expressed in different locations, indicating that only a combined modulation of both systems may cause dilatation along the entire bronchial tree. While all of these factors contribute to a rationale for a combination of muscarinic receptor antagonists and beta-adrenoceptor agonists, the full value of such combination as compared to monotherapy can only be determined in clinical studies
Monte Carlo techniques for real-time quantum dynamics
The stochastic-gauge representation is a method of mapping the equation of
motion for the quantum mechanical density operator onto a set of equivalent
stochastic differential equations. One of the stochastic variables is termed
the "weight", and its magnitude is related to the importance of the stochastic
trajectory. We investigate the use of Monte Carlo algorithms to improve the
sampling of the weighted trajectories and thus reduce sampling error in a
simulation of quantum dynamics. The method can be applied to calculations in
real time, as well as imaginary time for which Monte Carlo algorithms are
more-commonly used. The method is applicable when the weight is guaranteed to
be real, and we demonstrate how to ensure this is the case. Examples are given
for the anharmonic oscillator, where large improvements over stochastic
sampling are observed.Comment: 28 pages, submitted to J. Comp. Phy
Validation of the reasons for gambling questionnaire (RGQ) in a British population survey
Introduction. The aim of the study is to validate the five-dimensional structure of the Reasons for Gambling Questionnaire (RGQ) and to test the differences between different types of gamblers (i.e., offline gamblers who gambled in-person only vs.mixed-mode gamblers who gambled both online and offline) on the five dimensions of the RGQ. Methods. Data from the 2010 British Gambling Prevalence Survey (BGPS) were used. The analysed data comprised 5,677 individuals (52.7% female; mean age=47.64 years; SD=17.82). Confirmatory factor analysis and independent-samples t-tests were applied. Results. The five-dimensional structure of the RGQ wasconfirmed in the general sample and among gender and age subgroups. Furthermore, mixed-mode gamblers (MMGs) who gambled both online and offline had higher scores for enhancement, recreation and money motives than offline gamblers that gambled in-person only (IPGs). In addition among males, there was a significant difference in the scores for enhancement and recreation motives across MMGs and IPGs. Among past-year gamblers aged 16-34 years, MMGs had higher scores for enhancement, recreational and monetary motives than IPGs whilst among past-year gamblers aged 35-55years, MMGs had higher scores for enhancement and recreational motives than IPGs. Conclusions. The results are consistent with a previous test of the RGQ and the findings indicate that the RGQis a valid instrument to assess gambling motives among the general population
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