Antigen presenting capacity of murine splenic myeloid cells

BACKGROUND: The spleen is an important site for hematopoiesis. It supports development of myeloid cells from bone marrow-derived precursors entering from blood. Myeloid subsets in spleen are not well characterised although dendritic cell (DC) subsets are clearly defined in terms of phenotype, development and functional role. Recently a novel dendritic-like cell type in spleen named ‘L-DC’ was distinguished from other known dendritic and myeloid cells by its distinct phenotype and developmental origin. That study also redefined splenic eosinophils as well as resident and inflammatory monocytes in spleen. RESULTS: L-DC are shown to be distinct from known splenic macrophages and monocyte subsets. Using a new flow cytometric procedure, it has been possible to identify and isolate L-DC in order to assess their functional competence and ability to activate T cells both in vivo and in vitro. L-DC are readily accessible to antigen given intravenously through receptor-mediated endocytosis. They are also capable of CD8(+) T cell activation through antigen cross presentation, with subsequent induction of cytotoxic effector T cells. L-DC are MHCII(−) cells and unable to activate CD4(+) T cells, a property which clearly distinguishes them from conventional DC. The myeloid subsets of resident monocytes, inflammatory monocytes, neutrophils and eosinophils, were found to have varying capacities to take up antigen, but were uniformly unable to activate either CD4(+) T cells or CD8(+) T cells. CONCLUSION: The results presented here demonstrate that L-DC in spleen are distinct from other myeloid cells in that they can process antigen for CD8(+) T cell activation and induction of cytotoxic effector function, while both L-DC and myeloid subsets remain unable to activate CD4(+) T cells. The L-DC subset in spleen is therefore distinct as an antigen presenting cell

Hierarchical surface code for network quantum computing with modules of arbitrary size

The network paradigm for quantum computing involves interconnecting many modules to form a scalable machine. Typically it is assumed that the links between modules are prone to noise while operations within modules have significantly higher fidelity. To optimise fault tolerance in such architectures we introduce a hierarchical generalisation of the surface code: a small `patch' of the code exists within each module, and constitutes a single effective qubit of the logic-level surface code. Errors primarily occur in a two-dimensional subspace, i.e. patch perimeters extruded over time, and the resulting noise threshold for inter-module links can exceed ~ 10% even in the absence of purification. Increasing the number of qubits within each module decreases the number of qubits necessary for encoding a logical qubit. But this advantage is relatively modest, and broadly speaking a `fine grained' network of small modules containing only ~ 8 qubits is competitive in total qubit count versus a `course' network with modules containing many hundreds of qubits.Comment: 12 pages, 11 figure

Efficient variational quantum simulator incorporating active error minimisation

One of the key applications for quantum computers will be the simulation of other quantum systems that arise in chemistry, materials science, etc, in order to accelerate the process of discovery. It is important to ask: Can this be achieved using near future quantum processors, of modest size and under imperfect control, or must it await the more distant era of large-scale fault-tolerant quantum computing? Here we propose a variational method involving closely integrated classical and quantum coprocessors. We presume that all operations in the quantum coprocessor are prone to error. The impact of such errors is minimised by boosting them artificially and then extrapolating to the zero-error case. In comparison to a more conventional optimised Trotterisation technique, we find that our protocol is efficient and appears to be fundamentally more robust against error accumulation.Comment: 13 pages, 5 figures; typos fixed and small update

Stabilisers as a design tool for new forms of Lechner-Hauke-Zoller Annealer

In a recent paper Lechner, Hauke and Zoller (LHZ) described a means to translate a Hamiltonian of $N$ spin-$\frac{1}{2}$ particles with 'all-to-all' interactions into a larger physical lattice with only on-site energies and local parity constraints. LHZ used this mapping to propose a novel form of quantum annealing. Here we provide a stabiliser-based formulation within which we can describe both this prior approach and a wide variety of variants. Examples include a triangular array supporting all-to-all connectivity, and moreover arrangements requiring only $2N$ or $N\log N$ spins but providing interesting bespoke connectivities. Further examples show that arbitrarily high order logical terms can be efficiently realised, even in a strictly 2D layout. Our stabilisers can correspond to either even-parity constraints, as in the LHZ proposal, or as odd-parity constraints. Considering the latter option applied to the original LHZ layout, we note it may simplify the physical realisation since the required ancillas are only spin-$\frac{1}{2}$ systems (i.e. qubits, rather than qutrits) and moreover the interactions are very simple. We make a preliminary assessment of the impact of this design choices by simulating small (few-qubit) systems; we find some indications that the new variant may maintain a larger minimum energy gap during the annealing process.Comment: A dramatically expanded revision: we now show how to use our stabiliser formulation to construct a wide variety of new physical layouts, including ones with fewer than Order N^2 spins but custom connectivities, and a means to achieve higher order coupling even in 2

Privatization, concentration, and pressure for protection : a steel sector study

In considering whether to privatize a large state-owned steel enterprise in Argentina, the question arose: Would its sale to a consortium of large domestic enterprises, and the resulting increase in firm concentration, inevitably lead to cries for protection? To shed light on the question, the authors examine data for steel industries in the major industrial countries. They also construct a simulation of Argentina's steel sector to study the relationships between levels of industrial concentration, substitutability between domestic and imported steels, trade policy regimes, and mark-ups of domestic prices over international prices. Their simulation results show that heavier rents and economic distortions are generated through fixed-ratio import quotas (quotas that are a fixed proportion of domestic sales) than through use of a tariff or a fixed-quantity import quota. The results show why industries seeking protection prefer a fixed-ratio import restraint - a practice being used increasingly often in industrial countries. If there is not perfect substitutability between domestic and imported steels, the incentives for the Argentine industry to seek protection - particularly as a fixed-ratio quota - are greater, the more concentrated the industry is. The lesson for policymakers - who should be trying to minimize economic distortions - is that if protection is necessary, tariffs are preferable to import quotas, perhaps even to the point of making quota-type restrictions unconstitutional. The simulation results for Argentina confirm that the less substitutable domestic and foreign goods are, the higher the rents of domestic industry can extract. So, it is important for policymakers implementing privatization schemes to ease any explicit or implicit obstacles to imports by such measures as: (a) standardizing domestic product classifications with international classifications; (b) modernizing transportation facilities to improve the speed of shipment and communication; (c) reducing bureaucratic practices related to trade in goods and services; and (d) releasing foreign exchange restrictions. The goal should be to make a foreign transaction as easy as a domestic transaction.TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Markets and Market Access,Access to Markets,Environmental Economics&Policies,Economic Theory&Research