Atomic-Scale Magnetometry of Dynamic Magnetization

The spatial resolution of imaging magnetometers has benefited from scanning probe techniques. The requirement that the sample perturbs the scanning probe through a magnetic field external to its volume limits magnetometry to samples with pre-existing magnetization. We propose a magnetometer in which the perturbation is reversed: the probe's magnetic field generates a response of the sample, which acts back on the probe and changes its energy. For an NV^{-} spin center in diamond this perturbation changes the fine-structure splitting of the spin ground state. Sensitive measurement techniques using coherent detection schemes then permit detection of the magnetic response of paramagnetic and diamagnetic materials. This technique can measure the thickness of magnetically dead layers with better than 0.1 Å accuracy.

Spin-orbit-induced circulating currents in a semiconductor nanostructure

Circulating orbital currents produced by the spin-orbit interaction for a single electron spin in a quantum dot are explicitly evaluated at zero magnetic field, along with their effect on the total magnetic moment (spin and orbital) of the electron spin. The currents are dominated by coherent superpositions of the conduction and valence envelope functions of the electronic state, are smoothly varying within the quantum dot, and are peaked roughly halfway between the dot center and edge. Thus the spatial structure of the spin contribution to the magnetic moment (which is peaked at the dot center) differs greatly from the spatial structure of the orbital contribution. Even when the spin and orbital magnetic moments cancel (for g=0) the spin can interact strongly with local magnetic fields, e.g., from other spins, which has implications for spin lifetimes and spin manipulation.

Sparse sampling for assessment of drug exposure in toxicological studies

In support of animal toxicity testing of new drugs, toxicokinetics is designed to assess the systemic exposure of the animals to the drug across dose levels, genders, and periods of the study. In small rodents, repeated sampling may alter the health of the animals and jeopardize the toxicity evaluation. One conventional way to circumvent this limitation is to collect serial samples from satellite animals maintained as the main study animals but not monitored for toxicity. We evaluated, on a real example, whether the exposure could be assessed in the main animals from sparse samples. The only acceptable designs consisted of one single sample per animal repeated on two or three study days. In the rat 13-week oral toxicity study of a new chemical entity, both serial sampling in the satellite animals and sparse sampling in the main animals were applied. Similar measures of exposure and qualitative conclusions were derived from the two groups of animals. The very sparse design applied to the main group yielded adequate estimation of the animal exposure, even with a very simple non-compartmental approach. The population pharmacokinetics analysis of the sparse data with NONMEM provided additional information about drug disposition and the influence of the covariates.

IgG antibodies against an HLA antigen are associated with activated cytotoxic T cells against this antigen, IgM are not

Pre-existing alloantibodies against the mismatched HLA-A and HLA-B antigens of the donor, when present in current sera, are believed to be detrimental to kidney graft survival. When these antibodies are present only in historical sera, their immunoglobulin class has reported to be important with respect to the expected graft survival, IgG antibodies being associated with poor graft prognosis and IgM with reasonable graft survival. In the present study, we have tested whether the immunoglobulin class of anti-HLA antibodies is reflected in the activation state of CTLs directed against these HLA antigens as measured by their in vitro resistance or sensitivity to CsA. The results indicate that the presence of IgG anti-HLA antibodies is associated with the presence of activated CTLs (CsA resistant), whereas in the case of IgM antibodies, mainly naive CTLs (CsA sensitive) are found. This observation may explain the different prognoses of historical positive crossmatches due to IgG versus IgM alloantibodies.