Transition from an electron solid to the sequence of fractional quantum Hall states at very low Landau level filling factor

At low Landau level filling of a two-dimensional electron system, typically associated with the formation of an electron crystal, we observe local minima in Rxx at filling factors nu=2/11, 3/17, 3/19, 2/13, 1/7, 2/15, 2/17, and 1/9. Each of these developing fractional quantum Hall (FQHE) states appears only above a filling factor-specific temperature. This can be interpreted as the melting of an electron crystal and subsequent FQHE liquid formation. The observed sequence of FQHE states follow the series of composite fermion states emanating from nu=1/6 and nu=1/8

Timing of exercise for muscle strength and physical function in men initiating ADT for prostate cancer

© 2020, The Author(s). Background: Androgen deprivation therapy (ADT) in men with prostate cancer (PCa) results in adverse effects, including reduced muscle strength and physical function, potentially compromising daily functioning. We examined whether it was more efficacious to commence exercise at the onset of ADT rather than later in treatment to counter declines in strength and physical function. Methods: One-hundred-and-four men with PCa (68.3 ± 7.0 years) initiating ADT were randomised to immediate exercise (IMX, n = 54) or delayed exercise (DEL, n = 50) for 12 months. IMX comprised 6 months of supervised resistance/aerobic/impact exercise initiated at the onset of ADT with a 6-month follow-up. DEL comprised 6 months of usual care followed by 6 months of resistance/aerobic/impact exercise. Upper and lower body muscle strength and physical function were assessed at baseline, 6 and 12 months. Results: There was a significant difference for all strength measures at 6 months favouring IMX (P \u3c 0.001), with net differences in leg press, seated row and chest press strength of 19.9 kg (95% CI, 12.3–27.5 kg), 5.6 kg (3.8–7.4 kg) and 4.3 kg (2.7–5.8 kg), respectively. From 7 to 12 months, DEL increased in all strength measures (P \u3c 0.001), with no differences between groups at 12 months. Similarly, physical function improved (P \u3c 0.001) in IMX compared with DEL at 6 months for the 6-m fast walk (−0.2, 95% CI −0.3 to −0.1 s), 400-m walk (−9.7, −14.8 to −4.6 s), stair climb (−0.4, −0.6 to −0.2 s) and chair rise (−1.0, −1.4 to −0.7 s), with no differences between groups by 12 months, except for the 6-m fast walk (P \u3c 0.001). Conclusion: Exercise either at the onset or after 6 months of ADT preserves/enhances muscle strength and physical function. However, to avoid initial treatment-related adverse effects on strength and function, exercise therapy should be implemented with initiation of ADT

Excitons and charged excitons in semiconductor quantum wells

A variational calculation of the ground-state energy of neutral excitons and of positively and negatively charged excitons (trions) confined in a single-quantum well is presented. We study the dependence of the correlation energy and of the binding energy on the well width and on the hole mass. The conditional probability distribution for positively and negatively charged excitons is obtained, providing information on the correlation and the charge distribution in the system. A comparison is made with available experimental data on trion binding energies in GaAs-, ZnSe-, and CdTe-based quantum well structures, which indicates that trions become localized with decreasing quantum well width.Comment: 9 pages, 11 figure

Aharonov-Bohm signature for neutral excitons in type-II quantum dot ensembles

It is commonly believed that the Aharonov-Bohm (AB) effect is a typical feature of the motion of a charged particle interacting with the electromagnetic vector potential. Here we present a magnetophotoluminescence study of type-II InP/GaAs self-assembled quantum dots, unambiguously revealing the Aharonov-Bohm-type oscillations for neutral excitons when the hole ground state changes its angular momentum from lh = 0 to lh = 1, 2, and 3. The hole ring parameters derived from a simple model are in excellent agreement with the structural parameters for this system.Comment: Revised version, 10 pages, 3 figure

Typification and authorship of Drosera intermedia (Droseraceae)

Drosera intermedia is lectotypified with the herbarium specimen on which the type drawing in the 1798 protologue was based. The collection history of the specimen, the history of the botanical drawing as original material, and the correct nomenclatural author and publication date of the name are presented based on historical notes and literature. Additionally, the global distribution of the species is given, including the first record from Africa

Immediate versus delayed exercise in men initiating androgen deprivation: effects on bone density and soft tissue composition

OBJECTIVES: To examine whether it is more efficacious to commence exercise medicine in men with prostate cancer at the onset of androgen-deprivation therapy (ADT) rather than later on during treatment to preserve bone and soft-tissue composition, as ADT results in adverse effects including: reduced bone mineral density (BMD), loss of muscle mass, and increased fat mass (FM). PATIENTS AND METHODS: In all, 104 patients with prostate cancer, aged 48-84 years initiating ADT, were randomised to immediate exercise (IMEX, n = 54) or delayed exercise (DEL, n = 50) conditions. The former consisted of 6 months of supervised resistance/aerobic/impact exercise and the latter comprised 6 months of usual care followed by 6 months of the identical exercise programme. Regional and whole body BMD, lean mass (LM), whole body FM and trunk FM, and appendicular skeletal muscle (ASM) were assessed by dual X-ray absorptiometry, and muscle density by peripheral quantitative computed tomography at baseline, and at 6 and 12 months. RESULTS: There was a significant time effect (P \u3c 0.001) for whole body, spine and hip BMD with a progressive loss in the IMEX and DEL groups, although lumbar spine BMD was largely preserved in the IMEX group at 6 months compared with the DEL group (-0.4% vs -1.6%). LM, ASM, and muscle density were preserved in the IMEX group at 6 months, declined in the DEL group at 6 months (-1.4% to -2.5%) and then recovered at 12 months after training. FM and trunk FM increased (P \u3c 0.001) over the 12-month period in the IMEX (7.8% and 4.5%, respectively) and DEL groups (6.5% and 4.3%, respectively). CONCLUSIONS: Commencing exercise at the onset of ADT preserves lumbar spine BMD, muscle mass, and muscle density. To avoid treatment-related adverse musculoskeletal effects, exercise medicine should be prescribed and commenced at the onset of ADT

Probing the potential landscape inside a two-dimensional electron-gas

We report direct observations of the scattering potentials in a two-dimensional electron-gas using electron-beam diffaction-experiments. The diffracting objects are local density-fluctuations caused by the spatial and charge-state distribution of the donors in the GaAs-(Al,Ga)As heterostructures. The scatterers can be manipulated externally by sample illumination, or by cooling the sample down under depleted conditions.Comment: 4 pages, 4 figure

Stability of trions in strongly spin-polarized two-dimensional electron gases

Low-temperature magneto-photoluminescence studies of negatively charged excitons (X- trions) are reported for n-type modulation-doped ZnSe/Zn(Cd,Mn)Se quantum wells over a wide range of Fermi energy and spin-splitting. The magnetic composition is chosen such that these magnetic two-dimensional electron gases (2DEGs) are highly spin-polarized even at low magnetic fields, throughout the entire range of electron densities studied (5e10 to 6.5e11 cm^-2). This spin polarization has a pronounced effect on the formation and energy of X-, with the striking result that the trion ionization energy (the energy separating X- from the neutral exciton) follows the temperature- and magnetic field-tunable Fermi energy. The large Zeeman energy destabilizes X- at the nu=1 quantum limit, beyond which a new PL peak appears and persists to 60 Tesla, suggesting the formation of spin-triplet charged excitons.Comment: 5 pages (RevTex), 4 embedded EPS figs. Submitted to PRB-R

Single and vertically coupled type II quantum dots in a perpendicular magnetic field: exciton groundstate properties

The properties of an exciton in a type II quantum dot are studied under the influence of a perpendicular applied magnetic field. The dot is modelled by a quantum disk with radius $R$, thickness $d$ and the electron is confined in the disk, whereas the hole is located in the barrier. The exciton energy and wavefunctions are calculated using a Hartree-Fock mesh method. We distinguish two different regimes, namely $d<<2R$ (the hole is located at the radial boundary of the disk) and $d>>2R$ (the hole is located above and below the disk), for which angular momentum $(l)$ transitions are predicted with increasing magnetic field. We also considered a system of two vertically coupled dots where now an extra parameter is introduced, namely the interdot distance $d_{z}$. For each $l_{h}$ and for a sufficient large magnetic field, the ground state becomes spontaneous symmetry broken in which the electron and the hole move towards one of the dots. This transition is induced by the Coulomb interaction and leads to a magnetic field induced dipole moment. No such symmetry broken ground states are found for a single dot (and for three vertically coupled symmetric quantum disks). For a system of two vertically coupled truncated cones, which is asymmetric from the start, we still find angular momentum transitions. For a symmetric system of three vertically coupled quantum disks, the system resembles for small $d_{z}$ the pillar-like regime of a single dot, where the hole tends to stay at the radial boundary, which induces angular momentum transitions with increasing magnetic field. For larger $d_{z}$ the hole can sit between the disks and the $l_{h}=0$ state remains the groundstate for the whole $B$-region.Comment: 11 pages, 16 figure

Application of Jain and Munczek's bound-state approach to gamma gamma-processes of pi0, eta_c and eta_b

We point out the problems affecting most quark--antiquark bound state approaches when they are faced with the electromagnetic processes dominated by Abelian axial anomaly. However, these problems are resolved in the consistently coupled Schwinger-Dyson and Bethe-Salpeter approach. Using one of the most successful variants of this approach, we find the dynamically dressed propagators of the light u and d quarks, as well as the heavy c and b quarks, and find the Bethe-Salpeter amplitudes for their bound states pi0, eta_c and \eta_b. Thanks to incorporating the dynamical chiral symmetry breaking, the pion simultaneously appears as the (pseudo)Goldstone boson. We give the theoretical predictions for the gamma-gamma decay widths of pi0, eta_c and eta_b, and for the pi0 gamma* -> gamma transition form factor, and compare them with experiment. In the chiral limit, the axial-anomaly result for pi0->gamma-gamma is reproduced analytically in the consistently coupled Schwinger-Dyson and Bethe-Salpeter approach, provided that the quark-photon vertex is dressed consistently with the quark propagator, so that the vector Ward-Takahashi identity of QED is obeyed. On the other hand, the present approach is also capable of quantitatively describing systems of heavy quarks, concretely eta_c and possibly eta_b, and their gamma-gamma decays. We discuss the reasons for the broad phenomenological success of the bound-state approach of Jain and Munczek.Comment: RevTeX, 37 pages, 7 eps figures, submitted to Int. J. Mod. Phys.