Acceptor binding energies in GaN and AlN

We employ effective mass theory for degenerate hole-bands to calculate the acceptor binding energies for Be, Mg, Zn, Ca, C and Si substitutional acceptors in GaN and AlN. The calculations are performed through the 6$\times$6 Rashba-Sheka-Pikus and the Luttinger-Kohn matrix Hamiltonians for wurtzite (WZ) and zincblende (ZB) crystal phases, respectively. An analytic representation for the acceptor pseudopotential is used to introduce the specific nature of the impurity atoms. The energy shift due to polaron effects is also considered in this approach. The ionization energy estimates are in very good agreement with those reported experimentally in WZ-GaN. The binding energies for ZB-GaN acceptors are all predicted to be shallower than the corresponding impurities in the WZ phase. The binding energy dependence upon the crystal field splitting in WZ-GaN is analyzed. Ionization levels in AlN are found to have similar `shallow' values to those in GaN, but with some important differences, which depend on the band structure parameterizations, especially the value of crystal field splitting used.Comment: REVTEX file - 1 figur

General boundary conditions for the envelope function in multiband k.p model

We have derived general boundary conditions (BC) for the multiband envelope functions (which do not contain spurious solutions) in semiconductor heterostructures with abrupt heterointerfaces. These BC require the conservation of the probability flux density normal to the interface and guarantee that the multiband Hamiltonian be self--adjoint. The BC are energy independent and are characteristic properties of the interface. Calculations have been performed of the effect of the general BC on the electron energy levels in a potential well with infinite potential barriers using a coupled two band model. The connection with other approaches to determining BC for the envelope function and to the spurious solution problem in the multiband k.p model are discussed.Comment: 15 pages, 2 figures; to be published in Phys. Rev. B 65, March 15 issue 200

Development of an in vitro protocol for a difficult-to-propagate endemic Australian dryland sedge species Mesomelaena pseudostygia (Cyperaceae)

In vitro propagation for Mesomelaena pseudostygia a difficult-to-propagate dryland sedge species (Cyperaceae) endemic to Western Australia is described. Multiple avenues to in vitro propagation were investigated: shoot culture, organogenesis and somatic embryogenesis, with zygotic embryos as initiation material. The highest multiplication rate for shoots was 3.4 ± 1.0 after 6 wk on basal medium (1/2 strength Murashige and Skoog) with 2.5 μM kinetin and 0.5 μM 6-benzylaminopurine. Shoots achieved peak rooting (83%) following a pulse treatment on basal medium containing 10 μM indolebutyric acid and 2 μM α-naphthaleneacetic acid for 7 wk, followed by transfer to medium (without growth regulators) for a further 7 wk. Alternatively, in vitro grown shoots were pulse treated on basal medium with both 100 μM indolebutyric acid and 20 μM α-naphthaleneacetic acid for 1 wk then placed in Rockwool plugs (under propagation house conditions) for another 7 wk resulting in 63% root induction. Rooted plantlets were also successfully transferred to potting mixture either in Rockwool plugs or bare rooted and maintained in propagation house conditions with ≥95% survival after 7 wk. These results indicate that micropropagation of M. pseudostygia is feasible for small to medium scale restoration purposes. The highest frequency of callus induction was from cultured zygotic embryos on basal medium with 5 μM α-naphthaleneacetic acid, whereas 2,4-dichlorophenoxacetic acid (2 or 5 μM) produced the largest callus sizes. A low frequency of shoot regeneration occurred in zygotic callus tissues in basal medium treatments containing cytokinin (kinetin or thidiazuron at 1 μM). A small proportion (<20%) of zygotic embryo callus explants from 2,4-dichlorophenoxyacetic acid treatments were found to be embryogenic, firstly developing embryo-like structures after 2 wk on basal medium (minus plant growth hormones), that continued to develop with approximately one in twenty germinating after a further 4 wk on basal medium to form small plantlets. Further optimisation is needed to improve somatic embryogenesis efficiency for mass propagation

The 2021 European Group on Graves' orbitopathy (EUGOGO) clinical practice guidelines for the medical management of Graves' orbitopathy

Graves' orbitopathy (GO) is the main extrathyroidal manifestation of Graves' disease (GD). Choice of treatment should be based on the assessment of clinical activity and severity of GO. Early referral to specialized centers is fundamental for most patients with GO. Risk factors include smoking, thyroid dysfunction, high serum level of thyrotropin receptor antibodies, radioactive iodine (RAI) treatment, and hypercholesterolemia. In mild and active GO, control of risk factors, local treatments, and selenium (selenium-deficient areas) are usually sufficient; if RAI treatment is selected to manage GD, low-dose oral prednisone prophylaxis is needed, especially if risk factors coexist. For both active moderate-to-severe and sight-threatening GO, antithyroid drugs are preferred when managing Graves' hyperthyroidism. In moderate-to-severe and active GO i.v. glucocorticoids are more effective and better tolerated than oral glucocorticoids. Based on current evidence and efficacy/safety profile, costs and reimbursement, drug availability, long-term effectiveness, and patient choice after extensive counseling, a combination of i.v. methylprednisolone and mycophenolate sodium is recommended as first-line treatment. A cumulative dose of 4.5 g of i.v. methylprednisolone in 12 weekly infusions is the optimal regimen. Alternatively, higher cumulative doses not exceeding 8 g can be used as monotherapy in most severe cases and constant/inconstant diplopia. Second-line treatments for moderate-to-severe and active GO include (a) the second course of i.v. methylprednisolone (7.5 g) subsequent to careful ophthalmic and biochemical evaluation, (b) oral prednisone/prednisolone combined with either cyclosporine or azathioprine; (c) orbital radiotherapy combined with oral or i.v. glucocorticoids, (d) teprotumumab; (e) rituximab and (f) tocilizumab. Sight-threatening GO is treated with several high single doses of i.v. methylprednisolone per week and, if unresponsive, with urgent orbital decompression. Rehabilitative surgery (orbital decompression, squint, and eyelid surgery) is indicated for inactive residual GO manifestations