Optical Conductivity Anisotropy in the Undoped Three-Orbital Hubbard Model for the Pnictides

The resistivity anisotropy unveiled in the study of detwinned single crystals of the undoped 122 pnictides is here studied using the two-dimensional three-orbital Hubbard model in the mean-field approximation. Calculating the Drude weight in the x and y directions at zero temperature for a Q=(\pi,0) magnetically ordered state, the conductance along the antiferromagnetic direction is shown to be larger than along the ferromagnetic direction. This effect is caused by the suppression of the d_{yz} orbital at the Fermi surface, but additional insight based on the momentum dependence of the transitions induced by the current operator is provided. It is shown that the effective suppression of the inter-orbital hopping d_{xy} and d_{yz} along the y direction is the main cause of the anisotropy.Comment: 5 pages, 4 figs, submitted to PRB(RC

Optimal Control for Electron Shuttling

In this paper we apply an optimal control technique to derive control fields that transfer an electron between ends of a chain of donors or quantum dots. We formulate the transfer as an optimal steering problem, and then derive the dynamics of the optimal control. A numerical algorithm is developed to effectively generate control pulses. We apply this technique to transfer an electron between sites of a triple quantum dot and an ionized chain of phosphorus dopants in silicon. Using the optimal pulses for the spatial shuttling of phosphorus dopants, we then add hyperfine interactions to the Hamiltonian and show that a 500 G magnetic field will transfer the electron spatially as well as transferring the spin components of two of the four hyperfine states of the electron-nuclear spin pair.Comment: 9 pages, 3 figure

Effectiveness of folic acid fortified flour for prevention of neural tube defects in a high risk region

Despite efforts to tackle folate deficiency and Neural Tube Defects (NTDs) through folic acid fortification, its implementation is still lacking where it is needed most, highlighting the need for studies that evaluate the effectiveness of folic acid fortified wheat flour in a poor, rural, high-risk, NTD region of China. One of the most affected regions, Shanxi Province, was selected as a case study. A community intervention was carried out in which 16,648 women of child-bearing age received fortified flour (eight villages) and a control group received ordinary flour (three villages). NTD birth prevalence and biological indicators were measured two years after program initiation at endline only. The effect on the NTD burden was calculated using the disability-adjusted life years (DALYs) method. In the intervention group, serum folate level was higher than in the control group. NTDs in the intervention group were 68.2% lower than in the control group (OR = 0.313, 95% CI = 0.207-0473, p < 0.001). In terms of DALYs, burden in intervention group was approximately 58.5% lower than in the control group. Flour fortification was associated with lower birth prevalence and burden of NTDs in economically developing regions with a high risk of NTDs. The positive findings confirm the potential of fortification when selecting an appropriate food vehicle and target region. As such, this study provides support for decision makers aiming for the implementation of (mandatory) folic acid fortification in China

Radio-frequency resonant cavity measurements for rapid, accurate assessment of body composition and human exposure to electromagnetic fields

Body composition measurements play an important role in nutritional studies, renal medicine and sports science, while human exposure to electromagnetic fields (EMF) is an area of growing concern owing to the implementation of Directive 2013/35/EU on EMF. Resonant cavity techniques offer an attractive alternative to traditional methods in these fields, as they allow rapid, non-invasive measurements without using ionising radiation. At frequencies of a few tens of MHz, a large screened room can act as a cavity resonator. A human subject inside the room perturbs its low-order resonances, and the resulting shift in frequency depends on the tissue dielectric properties, which correlate strongly with water content. This approach has been well tested and shows good agreement with current methods of measuring total body water. The number of resonant modes increases rapidly with frequency, so if we instead use microwaves at 1GHz and above, many modes can be excited simultaneously. Adding a rotating paddle to the room creates a ‘stirred mode’ environment, where the body is effectively illuminated by microwave radiation from all directions. For EMF exposure studies this a more realistic scenario than considering only a single direction and polarisation. The average absorption cross section (ACS), which is closely related to specific absorption rate (SAR), can be rapidly obtained over a very broad band (1GHz to 15GHz and beyond), whereas the alternative is detailed computer simulations that take many hours for just a single frequency. At these microwave frequencies, the field penetration into tissues is a few cm, so the ACS gives useful information about the composition of tissues near the body surface. Normalising the ACS to body surface area gives us an ‘absorption efficiency’ that is independent of body size. Results will be presented of the relationship between this parameter and the thickness of subcutaneous body fat. Both techniques are comfortable for the subject, use safe levels (around 1mW) of non-ionising radiation, and allow measurements to be made in less than 10min

Highly anisotropic resistivities in the double-exchange model for strained manganites

The highly anisotropic resistivities in strained manganites are theoretically studied using the two-orbital double-exchange model. At the nanoscale, the anisotropic double-exchange and Jahn-Teller distortions are found to be responsible for the robust anisotropic resistivities observed here via Monte Carlo simulations. An unbalanced in the population of orbitals caused by strain is responsible for these effects. In contrast, the anisotropic superexchange is found to be irrelevant to explain our results. Our model study suggests that highly anisotropic resistivities could be present in a wide range of strained manganites, even without (sub)micrometer-scale phase separation. In addition, our calculations also confirm the formation of anisotropic clusters in phase-separated manganites, which magnifies the anisotropic resistivities.Comment: 7 pages, 4 figure