1,659 research outputs found
Spending time with money: from shared values to social connectivity
This article has been made available through the Brunel Open Access Publishing Fund.There is a rapidly growing momentum driving the development of mobile payment systems for co-present interactions, using near-field communication on smartphones and contactless payment systems. The design (and marketing) imperative for this is to enable faster, simpler, effortless and secure transactions, yet our evidence shows that this focus on reducing transactional friction may ignore other important features around making payments. We draw from empirical data to consider user interactions around financial exchanges made on mobile phones. Our findings examine how the practices around making payments support people in making connections, to other people, to their communities, to the places they move through, to their environment, and to what they consume. While these social and community bonds shape the kinds of interactions that become possible, they also shape how users feel about, and act on, the values that they hold with their co-users. We draw implications for future payment systems that make use of community connections, build trust, leverage transactional latency, and generate opportunities for rich social interactions
How to wire a 1000-qubit trapped ion quantum computer
One of the most formidable challenges of scaling up quantum computers is that
of control signal delivery. Today's small-scale quantum computers typically
connect each qubit to one or more separate external signal sources. This
approach is not scalable due to the I/O limitations of the qubit chip,
necessitating the integration of control electronics. However, it is no small
feat to shrink control electronics into a small package that is compatible with
qubit chip fabrication and operation constraints without sacrificing
performance. This so-called "wiring challenge" is likely to impact the
development of more powerful quantum computers even in the near term. In this
paper, we address the wiring challenge of trapped-ion quantum computers. We
describe a control architecture called WISE (Wiring using Integrated Switching
Electronics), which significantly reduces the I/O requirements of ion trap
quantum computing chips without compromising performance. Our method relies on
judiciously integrating simple switching electronics into the ion trap chip -
in a way that is compatible with its fabrication and operation constraints -
while complex electronics remain external. To demonstrate its power, we
describe how the WISE architecture can be used to operate a fully connected
1000-qubit trapped ion quantum computer using ~ 200 signal sources at a speed
of ~ 40 - 2600 quantum gate layers per second
A phased array-based method for damage detection and localization in thin plates
A method for damage localization based on the phased array idea has been developed. Four arrays oftransducers are used to perform a beam-forming procedure. Each array consists of nine transducersplaced along a line, which are able to excite and register elastic waves. The A0 Lamb wave mode hasbeen chosen for the localization method. The arrays are placed in such a way that the angulardifference between them is 458 and the rotation point is the middle transducer, which is common for allthe arrays. The idea has been tested on a square aluminium plate modeled by the Spectral Element Method. Two types of damage were considered, namely distributed damage, which was modeled asstiffness reduction, and cracks, modeled as separation of nodes between selected spectral elements.The plate is excited by a wave packet. The whole array system is placed in the middle of the plate.Each linear phased array in the system acts independently and produces maps of a scanned fieldbased on the beam-forming procedure. These maps are made of time signals (transferred to spacedomain) that represent the difference between the damaged plate signals and those from the intactplate. An algorithm was developed to join all four maps. The final map is modified by proposed signal processing algorithm to indicate the damaged area of the plate more precisely. The problem fordamage localization was investigated and exemplary maps confirming the effectiveness of theproposed system were obtained. It was also shown that the response of the introduced configurationremoves the ambiguity of damage localization normally present when a linear phased array is utilized.The investigation is based exclusively on numerical data
Enantioselective Synthesis of Pactamycin, a Complex Antitumor Antibiotic
Medicinal application of many complex natural products is precluded by the impracticality of their chemical synthesis. Pactamycin, the most structurally-intricate aminocyclopentitol antibiotic, displays potent anti-prolific properties across multiple phylogenetic domains, but is highly cytotoxic. A limited number of analogs produced by genetic engineering technologies show reduced cytotoxicity against mammalian cells, renewing promise for therapeutic applications. For decades, an efficient synthesis of pactamycin amenable to analog derivatizations has eluded researchers. Herein, we present a short asymmetric total synthesis of pactamycin. An enantioselective Mannich reaction/symmetry-breaking reduction sequence was designed to enable assembly of the entire carbon core skeleton in under five steps and control critical three-dimensional (stereochemical) functional group relationships. This modular route totals fifteen steps and is immediately amenable for structural analog synthesis
α-Amination of keto-nitrones via Multihetero-Cope rearrangement employing an imidoyl chloride reagent
α-Aminations of ketone-derived nitrones have been developed via [3,3]-rearrangement of the intermediates generated upon condensation with imidoyl chlorides. Careful reagent selection provides synthetically attractive amino protecting groups. The enediamide or α′-carbamoyl enamide products can be hydrolyzed to the desired carbonyl, or exposed to electrophiles for further α-functionalization
Diastereocontrolled Construction of Pactamycin’s Complex Ureido Triol Functional Array
An advanced intermediate in a projected synthesis of pactamycin has been prepared. Early installation of the C1-dimethylurea functionality allows for its participation in a diastereoselective, chelation-controlled addition of organometal nucleophiles to the C5 prochiral ketone. Four of the molecule's six stereocenters are set with a ketone functional handle provided for subsequent manipulation
Asymmetric Synthesis of the Aminocyclitol Pactamycin, a Universal Translocation Inhibitor
An asymmetric total synthesis of the aminocyclopentitol pactamycin is described, which delivers the title compound in 15 steps from 2,4-pentanedione. Critical to this approach was the exploitation of a complex symmetry-breaking reduction strategy to assemble the C1, C2, and C7 relative stereochemistry within the first four steps of the synthesis. Multiple iterations of this reduction strategy are described, and a thorough analysis of stereochemical outcomes is detailed. In the final case, an asymmetric Mannich reaction was developed to install a protected amine directly at the C2 position. Symmetry-breaking reduction of this material gave way to a remarkable series of stereochemical outcomes leading to the title compound without recourse to non-strategic downstream manipulations. This synthesis is immediately accommodating to the facile preparation of structural analogs
Anomalous f-electron Hall Effect in the Heavy-Fermion System CeTIn (T = Co, Ir, or Rh)
The in-plane Hall coefficient of CeRhIn, CeIrIn, and
CeCoIn and their respective non-magnetic lanthanum analogs are reported
in fields to 90 kOe and at temperatures from 2 K to 325 K. is
negative, field-independent, and dominated by skew-scattering above 50 K
in the Ce compounds. becomes increasingly negative below 50 K
and varies with temperature in a manner that is inconsistent with skew
scattering. Field-dependent measurements show that the low-T anomaly is
strongly suppressed when the applied field is increased to 90 kOe. Measurements
on LaRhIn, LaIrIn, and LaCoIn indicate that the same
anomalous temperature dependence is present in the Hall coefficient of these
non-magnetic analogs, albeit with a reduced amplitude and no field dependence.
Hall angle () measurements find that the ratio
varies as below 20 K for all
three Ce-115 compounds. The Hall angle of the La-115 compounds follow this
T-dependence as well. These data suggest that the electronic-structure
contribution dominates the Hall effect in the 115 compounds, with -electron
and Kondo interactions acting to magnify the influence of the underlying
complex band structure. This is in stark contrast to the situation in most
and heavy-fermion compounds where the normal carrier contribution to the
Hall effect provides only a small, T-independent background to Comment: 23 pages and 8 figure
Voltage control of nuclear spin in ferromagnetic Schottky diodes
We employ optical pump-probe spectroscopy to investigate the voltage
dependence of spontaneous electron and nuclear spin polarizations in hybrid
MnAs/n-GaAs and Fe/n-GaAs Schottky diodes. Through the hyperfine interaction,
nuclear spin polarization that is imprinted by the ferromagnet acts on
conduction electron spins as an effective magnetic field. We demonstrate tuning
of this nuclear field from <0.05 to 2.4 kG by varying a small bias voltage
across the MnAs device. In addition, a connection is observed between the diode
turn-on and the onset of imprinted nuclear polarization, while traditional
dynamic nuclear polarization exhibits relatively little voltage dependence.Comment: Submitted to Physical Review B Rapid Communications. 15 pages, 3
figure
Unusual giant magnetostriction in the ferrimagnet GdCaMnO
We report an unusual giant linear magnetostrictive effect in the ferrimagnet
GdCaMnO (80 K). Remarkably, the
magnetostriction, negative at high temperature (), becomes
positive below 15 K when the magnetization of the Gd sublattice overcomes the
magnetization of the Mn sublattice. A rather simple model where the magnetic
energy competes against the elastic energy gives a good account of the observed
results and confirms that Gd plays a crucial role in this unusual observation.
Unlike previous works in manganites where only striction associated with 3
Mn orbitals is considered, our results show that the lanthanide 4 orbitals
related striction can be very important too and it cannot be disregarded.Comment: 6 pages, 3 figure
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