397 research outputs found
Cross-verification of independent quantum devices
Quantum computers are on the brink of surpassing the capabilities of even the
most powerful classical computers. This naturally raises the question of how
one can trust the results of a quantum computer when they cannot be compared to
classical simulation. Here we present a verification technique that exploits
the principles of measurement-based quantum computation to link quantum
circuits of different input size, depth, and structure. Our approach enables
consistency checks of quantum computations within a device, as well as between
independent devices. We showcase our protocol by applying it to five
state-of-the-art quantum processors, based on four distinct physical
architectures: nuclear magnetic resonance, superconducting circuits, trapped
ions, and photonics, with up to 6 qubits and 200 distinct circuits
Conformational Dependence of a Protein Kinase Phosphate Transfer Reaction
Atomic motions and energetics for a phosphate transfer reaction catalyzed by
the cAMP-dependent protein kinase (PKA) are calculated by plane-wave density
functional theory, starting from structures of proteins crystallized in both
the reactant conformation (RC) and the transition-state conformation (TC). In
the TC, we calculate that the reactants and products are nearly isoenergetic
with a 0.2 eV barrier; while phosphate transfer is unfavorable by over 1.2 eV
in the RC, with an even higher barrier. With the protein in the TC, the motions
involved in reaction are small, with only P and the catalytic proton
moving more than 0.5 \AA. Examination of the structures reveals that in the RC
the active site cleft is not completely closed and there is insufficient space
for the phosphorylated serine residue in the product state. Together, these
observations imply that the phosphate transfer reaction occurs rapidly and
reversibly in a particular conformation of the protein, and that the reaction
can be gated by changes of a few tenths of an \AA in the catalytic site.Comment: revtex4, 7 pages, 4 figures, to be submitted to Scienc
Not entirely displacement: conceptualizing relocation in Ethiopia and South Africa as “disruptive re-placement”
Residents’ lived experiences of movement into state directed housing frequently evidence contradictory outcomes. Often, movement is articulated in terms of displacement, noting its profoundly negative outcomes. However, displacement does not always fully capture contradictions, particularly where housing programmes form part of wider developmental strategies, themselves ambiguous in practice. Adopting a relational analysis, the paper argues for consideration of new sites of settlement relative to previous locations through a critical evaluation of place, as well as accounting for dynamism of urban change over time. Framings must capture residents varied and contradictory lived experiences and the relationality of place experiences. Contributing to work in this field, this paper calls for a broader analytical framing, named here as “disruptive re-placement”. Drawing on two different housing programmes, in South Africa and Ethiopia the paper charts movement into, and living in, state-led housing in three case study areas within three cities. It employs a ‘lived experiences’ methodology to understand these relocations, drawing on residents’ accounts of disruptive re-placement to examine the materialities of planned state-provided formal housing; the spatialities of disruptive re-placement; the economic and socio-political dimensions of these processes and the significance of temporality in shaping disruption. A continuum of disruptive and injurious re-placement, and a critique of the developmental state is used to articulate a just urban agenda in relation to relocation practices
Optical absorption spectra in fullerenes C60 and C70: Effects of Coulomb interactions, lattice fluctuations, and anisotropy
Effects of Coulomb interactions and lattice fluctuations in the optical
absorption spectra of C60 and C70 are theoretically investigated by using a
tight binding model with long-range Coulomb interaction and bond disorder.
Anisotropy effects in C70 are also considered. Optical spectra are calculated
by using the Hartree-Fock approximation followed by the configuration
interaction method. The main conclusions are as follows: (1) The broad peaks at
excitation energies, 3.7eV, 4.7eV, and 5.7eV, observed in experiments of C60
molecules in a solution are reasonably described by the present theory. Peak
positions and relative oscillator strengths are in overall agreement with the
experiments. The broadening of peaks by lattice fluctuations is well simulated
by the bond disorder model. (2) The optical gap of C70 is larger when the
electric field of light is parallel to the long axis of the molecule. The shape
of the frequency dispersion also depends on the orientation of the molecule.
These properties are common in the free electron model and the model with
Coulomb interactions. (3) The spectrum of C70 averaged over bond disorder and
random orientations is compared with experiments in a solution. There is an
overall agreement about the spectral shape. Differences in the spectra of C60
and C70 are discussed in connection with the symmetry reduction from a
soccerball to a rugbyball.Comment: PACS numbers: 78.66.Qn, 78.20.Dj, 71.35.+z, 31.20.Tz; LaTeX, 15
pages, 5 figures (Physical Review B); Note: Please request figures to
Authors. They will be sent via snail mai
Applications of the RHIC AC Dipoles and Their Expected Performance
Two AC dipoles with horizontal and vertical oscillating magnetic fields will be installed in RHIC. They will provide coherent oscillations for beam dynamic studies and betatron function measurements. The AC dipole with horizontal magnetic field will also be used to induce a full spin flip for RHIC polarized proton experiments. This note discusses the applications of the AC dipoles in RHIC and their expected parameter
4-[(Dimethylamino)methylidene]-2-(4-nitrophenyl)-1,3-oxazol-5(4H)-one
The title molecule, C12H11N3O4, is essentially planar, the r.m.s. deviation for all non-H atoms being 0.068 Å. An intramolecular C—H⋯N hydrogen bond occurs. The crystal packing is dominated by π–π interactions [shortest centroid–centroid distance = 3.6312 (16) Å], which lead to supramolecular chains that are linked into a three-dimensional network via C—H⋯O contacts. The crystal was found to be a non-merohedral twin (twin law −1 0 0/0 −1 0/ 0.784 0 1), the fractional contribution of the minor component being approximately 22%
Effects of acute sleep loss on leptin, ghrelin, and adiponectin in adults with healthy weight and obesity: a laboratory study
ObjectiveThis study investigated whether blood concentrations of leptin, ghrelin, and adiponectin are affected by acute total sleep deprivation in a sex- and weight-specific manner. MethodsA total of 44 participants (mean age 24.9 years; 20 women; 19 with obesity) participated in a crossover design, including one night of sleep deprivation and one night of sleep in the laboratory. After each night, fasting blood was collected. ResultsAfter sleep deprivation, fasting levels of leptin were lower (mean [SE], vs. sleep: 17.3 [2.6] vs. 18.6 [2.8] ng/mL), whereas those of ghrelin and adiponectin were higher (839.4 [77.5] vs. 741.4 [63.2] pg/mL and 7.5 [0.6] vs. 6.8 [0.6] mu g/mL, respectively; all p < 0.05). The changes in leptin and adiponectin following sleep loss were more pronounced among women. Furthermore, the ghrelin increase was stronger among those with obesity after sleep loss. Finally, the sleep loss-induced increase in adiponectin was more marked among normal-weight participants. ConclusionsAcute sleep deprivation reduces blood concentrations of the satiety hormone leptin. With increased blood concentrations of ghrelin and adiponectin, such endocrine changes may facilitate weight gain if persisting over extended periods of sleep loss. The observed sex- and weight-specific differences in leptin, ghrelin, and adiponectin call for further investigation.Radiolog
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