Biomedical subjects

J Kempe

Publications and source records attributed to J Kempe.

6 recordsLinked to original sources

PubMed2001

Separable states are more disordered globally than locally.

A remarkable feature of quantum entanglement is that an entangled state of two parties, Alice ( A) and Bob ( B), may be more disordered locally than globally. That is, S(A)>S(A,B), where S(*) is the von Neumann entropy. It is known that satisfaction of this inequality implies that a state is nonseparable. In this paper we prove the stronger result that for separable states the vector of eigenvalues of the density matrix of system AB is majorized by the vector of eigenvalues of the density matrix of system A alone. This gives a strong sense in which a separable state is more disordered globally than locally and a new necessary condition for separability of bipartite states in arbitrary dimensions.

Journal Article↗

PubMed2000

Universal quantum computation with the exchange interaction.

Various physical implementations of quantum computers are being investigated, although the requirements that must be met to make such devices a reality in the laboratory at present involve capabilities well beyond the state of the art. Recent solid-state approaches have used quantum dots, donor-atom nuclear spins or electron spins; in these architectures, the basic two-qubit quantum gate is generated by a tunable exchange interaction between spins (a Heisenberg interaction), whereas the one-qubit gates require control over a local magnetic field. Compared to the Heisenberg operation, the one-qubit operations are significantly slower, requiring substantially greater materials and device complexity--potentially contributing to a detrimental increase in the decoherence rate. Here we introduced an explicit scheme in which the Heisenberg interaction alone suffices to implement exactly any quantum computer circuit. This capability comes at a price of a factor of three in additional qubits, and about a factor of ten in additional two-qubit operations. Even at this cost, the ability to eliminate the complexity of one-qubit operations should accelerate progress towards solid-state implementations of quantum computation.

Journal Article↗

PubMed2000

Universal fault-tolerant quantum computation on decoherence-free subspaces

A general scheme to perform universal, fault-tolerant quantum computation within decoherence-free subspaces (DFSs) is presented. At most two-qubit interactions are required, and the system remains within the DFS throughout the entire implementation of a quantum gate. We show explicitly how to perform universal computation on clusters of the four-qubit DFS encoding one logical qubit each under spatially symmetric (collective) decoherence. Our results have immediate relevance to quantum computer implementations in which quantum logic is implemented through exchange interactions, such as the recently proposed spin-spin coupled quantum dot arrays and donor-atom arrays.

Journal Article↗

PubMed1980

Regulation of arachidonic acid metabolites in macrophages.

The lipids of mouse peritoneal macrophages contain high levels (25 mole percent) of esterified arachidonic acid (20:4). Following in vitro exposure to unopsonized zymosan, these cells synthesize and release oxygenated products of 20:4. Maximal levels of zymosan ingestion promote the release of 40-50% of the 20:4 content of cultures without loss of viabilitiy. Release of radiolabel from macrophages prelabeled with [3H]20:4 provides a quantitative measure for the synthesis of 20:4-derived products. Approximately 67% of the released 20:4 is recovered as prostaglandins (PG) (51% PGE and 16% 6-oxo-PGF1 alpha) and the remainder as apolar products tentatively identified as hydroxy-eicosatetraenoic acids. The kinetics of synthesis are comparable for both sets of products. A detailed examination of PGE synthesis indicated the PGE levels rise in parallel with phagocytosis during a continuous exposure of macrophages to zymosan. The concentration of particles determines the initial rate of PGE release, but the time-course of synthesis is finite (approximately 60 min), regardless of the zymosan dose. These observations are compatible with the notion that phagocytosis results in a burst of PG synthesis, the size of which is determined by the phagocytic stimulus. This is supported by the finding that secondary challenges of zymosan promote new rounds of PG synthesis by macrophages.

Animals↗

PubMed1980

Prostaglandin synthesis by macrophages requires a specific receptor-ligand interaction.

The ingestion of particles by macrophages leads to the prompt induction of prostaglandin (PG) synthesis. We have now dissected the endocytic process and examined the requirements of prostaglandin E (PGE) synthesis for particle attachment, membrane interiorization, and phagosome-lysosome fusion. Macrophages that were loaded with the polyanion dextran sulfate and exhibited a greater than 99% inhibition of phagosome-lysosome fusion produced normal amounts of PGE upon challenge with zymosan. Inhibition of membrane interiorization with cytochalasin D was similarly ineffective in blocking PGE synthesis. The addition of large numbers of unmodified polystyrene latex beads, which were readily ingested by macrophages, failed to stimulate PGE synthesis. However, when macrophages were challenged with latex beads coated with immune complexes, an increased synthesis of PGE resulted. No response occurred if the complex was prepared with the F(ab')2 fragment of IgG. Similar results occurred when nonphagocytizable Sephadex beads coated with immune complexes were employed. We conclude that particle binding to the Fc receptor of the macrophage plasma membrane is a sufficient stimulus for PGE synthesis.

Animals↗

PubMed1978

Very low density lipoprotein stimulation of triglyceride accumulation in rat preadipocyte cultures.

Exposure of cultured rat epididymal preadipocytes to human very low density lipoproteins (VLDL) resulted in the rapid accumulation of large amounts of cellular triglyceride which was accompanied by the appearance of numerous large cellular lipid inclusions. Addition of heparin produced a two-fold stimulation of lipoprotein induced triglyceride accumulation. Supplementation of the growth medium with either low density lipoprotein, oleic acid or artificial triglyceride emulsion did not produce cellular triglyceride levels equivalent to that obtained with VLDL. Fibroblastic cells from rat skin and lung did not accumulate triglycerides when exposed to VLDL and heparin.

Adipose Tissue↗