In this paper we show that electron-positron pairs can be pumped inexhaustibly with a constant production rate from the one dimensional potential well with oscillating depth or width. Bound states embedded in the the Dirac sea can be pulled out and p
ushed to the positive continuum, and become scattering states. Pauli block, which dominant the saturation of pair creation in the static super-critical potential well, can be broken by the ejection of electrons. We find that the width oscillating mode is more efficient that the depth oscillating mode. In the adiabatic limit, pair number as a function of upper boundary of the oscillating, will reveal the diving of the bound states.
New imaging techniques are in great demand for investigating underground plant roots systems which play an important role in crop production. Compared with other non-destructive imaging modalities, PET can image plant roots in natural soil and produc
e dynamic 3D functional images which reveal the temporal dynamics of plant-environment interactions. In this study, we combined PET with optical projection tomography (OPT) to evaluate its potential for plant root phenotyping. We used a dedicated high resolution plant PET imager that has a 14 cm transaxial and 10 cm axial field of views, and multi-bed imaging capability. The image resolution is around 1.25 mm using ML-EM reconstruction algorithm. B73 inbred maize seeds were germinated and then grown in a sealed jar with transparent gel-based media. PET scanning started on the day when the first green leaf appeared, and was carried out once a day for 5 days. Each morning, around 10 mCi of 11CO2 was administrated into a custom built plant labeling chamber. After 10 minutes, residual activity was flushed out with fresh air before a 2-h PET scan started. For the OPT imaging, the jar was placed inside an acrylic cubic container filled with water, illuminated with a uniform surface light source, and imaged by a DSLR camera from 72 angles to acquire optical images for OPT reconstruction. The same plant was imaged 3 times a day by the OPT system. Plant roots growth is measured from the optical images. Co-registered PET and optical images indicate that most of the hot spots appeared in later time points of the PET images correspond to the most actively growing root tips. The strong linear correlation between 11C allocation at root tips measured by PET and eventual root growth measured by OPT suggests that we can use PET as a phenotyping tool to measure how a plant makes subterranean carbon allocation decisions in different environmental scenarios.
We studied Sr2IrO4 and Sr3Ir2O7 using angle-resolved photoemission spectroscopy (ARPES), making direct experimental determinations of intra- and inter-cell coupling parameters as well as Mott correlations and gap sizes. The results are generally cons
istent with LDA+U+Spin-orbit coupling (SOC) calculations, though the calculations missed the momentum positions of the dominant electronic states and neglected the importance of inter-cell coupling on the size of the Mott gap. The calculations also ignore the correlation-induced spectral peak widths, which are critical for making a connection to activation energies determined from transport experiments. The data indicate a dimensionality-controlled Mott transition in these 5d transition-metal oxides (TMOs).
