Optically controlled spin-polarization memory effect on Mn delta-doped heterostrucutres

We investigated the dynamics of the interaction between spin-polarized photo-created carriers and Mn ions on InGaAs/GaAs:Mn structures. The carriers are confined in an InGaAs quantum well and the Mn ions come from a Mn delta-layer grown at the GaAs barrier close to the well. Even though the carriers and the Mn ions are spatially separated, the interaction between them is demonstrated by time-resolved spin-polarized photoluminescence measurements. Using a pre-pulse laser excitation with an opposite circular-polarization clearly reduces the polarization degree of the quantum-well emission for samples where a strong magnetic interaction is observed. The results demonstrate that the Mn ions act as a spin-memory that can be optically controlled by the polarization of the photocreated carriers. On the other hand, the spin-polarized Mn ions also affect the spin-polarization of the subsequently created carriers as observed by their spin relaxation time. These effects fade away with increasing time delays between the pulses as well as with increasing temperatures.Comment: 12 pages, 5 figure

Reference Values of Three-Dimensional Proximal Femur Parameters from Bone Densitometry Images in Healthy Subjects from Argentina

Objective: New methodologies for the assessment of bone mass from by DXA have been developed in the last years. The threedimensional analysis of the proximal femur by (3D-DXA) allows the evaluation of cortical and trabecular bone separately and has shown a good correlation with computed tomography. We aimed to obtain reference values in a healthy population of both sexesin Argentina.Methods: Adults female and male subjects (n=992) from four cities from Argentina were included. BMD (g/cm2) was measured by DXA on the femoral neck and total hip. The 3D analysis was performed with 3D-Shaper software (v2.9, Galgo Medical, Spain).The cortical BMD (sDens - mg/cm2) and trabecular volumetric BMD (trab vBMD - mg/cm3) were consider. The distribution of the data was evaluated with the Shapiro-Wilk test and parametricor non-parametric tests were used as appropriate. Data were expressed as mean±SD and p<0.05 was considered significant.Results: 75.5% women (n=749) and 24.5% men (n=243) were included. The mean age was 54.8±16.8 y and BMI was 27.3±5.4 kg/m2. The data according to each decade and a comparison with a references group (decade 20-30) are shown in the following table (*indicates significant differences compared to decade 20-30).Conclusion: A significant decrease in trabecular vBMD from D40 was observed in women, while in men this decrease was observed later (D60). The cortical parameter sDens was observed decreasefrom D50 in women and in men, an increase in D40 and cortical bone maintenance according to age was found.Fil: Brance, M. L.. Reumatología y Enfermedades Óseas; ArgentinaFil: Saravi, Fernando Daniel. Escuela de Medicina Nuclear; ArgentinaFil: Henríquez, M. M.. Escuela de Medicina Nuclear; ArgentinaFil: Longobardi, V.. Instituto de Investigaciones Metabólicas; ArgentinaFil: Zanchetta, M. B.. Instituto de Investigaciones Metabólicas; ArgentinaFil: Larroudé, M. S.. Centro de Diagnostico Rossi; ArgentinaFil: Ulla, M. R.. Instituto Latinoamericano de Investigaciones Médicas; ArgentinaFil: Matos, F.. Instituto Latinoamericano de Investigaciones Médicas; ArgentinaFil: Salerni, H.. No especifíca;Fil: Oliveri, María Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Inmunología, Genética y Metabolismo. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Inmunología, Genética y Metabolismo; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Bonanno, Marina Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Inmunología, Genética y Metabolismo. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Inmunología, Genética y Metabolismo; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Meneses, N. L.. No especifíca;Fil: Di Gregorio, S.. Fundacion Cetir.; EspañaFil: Brum, L. R.. Universidad Nacional de Rosario; ArgentinaWorld Congress on Osteoporosis, Osteoarthritis and Musculoskeletal DiseasesVirtualBélgicaInternational Osteoporosis FoundationEuropean Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Disease

Energy spectra of fractional quantum Hall systems in the presence of a valence hole

The energy spectrum of a two-dimensional electron gas (2DEG) in the fractional quantum Hall regime interacting with an optically injected valence band hole is studied as a function of the filling factor $\nu$ and the separation $d$ between the electron and hole layers. The response of the 2DEG to the hole changes abruptly at $d$ of the order of the magnetic length $\lambda$. At $d<\lambda$, the hole binds electrons to form neutral ($X$) or charged ($X^-$) excitons, and the photoluminescence (PL) spectrum probes the lifetimes and binding energies of these states rather than the original correlations of the 2DEG. The ``dressed exciton'' picture (in which the interaction between an exciton and the 2DEG was proposed to merely enhance the exciton mass) is questioned. Instead, the low energy states are explained in terms of Laughlin correlations between the constituent fermions (electrons and $X^-$'s) and the formation of two-component incompressible fluid states in the electron--hole plasma. At $d>2\lambda$, the hole binds up to two Laughlin quasielectrons (QE) of the 2DEG to form fractionally charged excitons $h$QE$_n$. The previously found ``anyon exciton'' $h$QE$_3$ is shown to be unstable at any value of $d$. The critical dependence of the stability of different $h$QE$_n$ complexes on the presence of QE's in the 2DEG leads to the observed discontinuity of the PL spectrum at $\nu={1\over3}$ or ${2\over3}$.Comment: 16 pages, 14 figures, submitted to PR

Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Electron transport through double quantum dots

Electron transport experiments on two lateral quantum dots coupled in series are reviewed. An introduction to the charge stability diagram is given in terms of the electrochemical potentials of both dots. Resonant tunneling experiments show that the double dot geometry allows for an accurate determination of the intrinsic lifetime of discrete energy states in quantum dots. The evolution of discrete energy levels in magnetic field is studied. The resolution allows to resolve avoided crossings in the spectrum of a quantum dot. With microwave spectroscopy it is possible to probe the transition from ionic bonding (for weak inter-dot tunnel coupling) to covalent bonding (for strong inter-dot tunnel coupling) in a double dot artificial molecule. This review on the present experimental status of double quantum dot studies is motivated by their relevance for realizing solid state quantum bits.Comment: 32 pages, 31 figure

Optical anisotropy in vertically coupled quantum dots

We have studied the polarization of surface and edge-emitted photoluminescence (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD’s) grown by molecular beam epitaxy. The PL polarization is found to be strongly dependent on the number of stacked layers. While single-layer and 3-layer structures show only a weak TE polarization, it is enhanced for 10-layer stacks. The 20-layer stacks additionally show a low-energy side-band of high TE polarization, which is attributed to laterally coupled QD’s forming after the growth of many layers by lateral coalescence of QD’s in the upper layers. While in the single, 3- and 10-layer stacks, both TE polarized PL components are stronger than the TM component, the [110] TE component is weaker than the TM component in the 20-layer stack. This polarization reversal is attributed to an increasing vertical coupling with increasing layer number due to increasing dot size

Hygienisation, gentrification, and urban displacement in Brazil

This article engages recent debates over gentrification and urban displacement in the global South. While researchers increasingly suggest that gentrification is becoming widespread in “Southern” cities, others argue that such analyses overlook important differences in empirical context and privilege EuroAmerican theoretical frameworks. To respond to this debate, in this article, we outline the concept of higienização (hygienisation), arguing that it captures important contextual factors missed by gentrification. Hygienisation is a Brazilian term that describes a particular form of urban displacement, and is directly informed by legacies of colonialism, racial and class stigma, informality, and state violence. Our objective is to show how “Southern” concepts like hygienisation help urban researchers gain better insight into processes of urban displacement, while also responding to recent calls to decentre and provincialise urban theory

Exercise training prevents oxidative stress and ubiquitin-proteasome system overactivity and reverse skeletal muscle atrophy in heart failure

Background: Heart failure (HF) is known to lead to skeletal muscle atrophy and dysfunction. However, intracellular mechanisms underlying HF-induced myopathy are not fully understood. We hypothesized that HF would increase oxidative stress and ubiquitin-proteasome system (UPS) activation in skeletal muscle of sympathetic hyperactivity mouse model. We also tested the hypothesis that aerobic exercise training (AET) would reestablish UPS activation in mice and human HF. Methods/Principal Findings: Time-course evaluation of plantaris muscle cross-sectional area, lipid hydroperoxidation, protein carbonylation and chymotrypsin-like proteasome activity was performed in a mouse model of sympathetic hyperactivity-induced HF. At the 7th month of age, HF mice displayed skeletal muscle atrophy, increased oxidative stress and UPS overactivation. Moderate-intensity AET restored lipid hydroperoxides and carbonylated protein levels paralleled by reduced E3 ligases mRNA levels, and reestablished chymotrypsin-like proteasome activity and plantaris trophicity. In human HF (patients randomized to sedentary or moderate-intensity AET protocol), skeletal muscle chymotrypsin-like proteasome activity was also increased and AET restored it to healthy control subjects' levels. Conclusions: Collectively, our data provide evidence that AET effectively counteracts redox imbalance and UPS overactivation, preventing skeletal myopathy and exercise intolerance in sympathetic hyperactivity-induced HF in mice. Of particular interest, AET attenuates skeletal muscle proteasome activity paralleled by improved aerobic capacity in HF patients, which is not achieved by drug treatment itself. Altogether these findings strengthen the clinical relevance of AET in the treatment of HF.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2006/61523-7, 2006/58460-4]Conselho Nacional de Pesquisa e Desenvolvimento (CNPq) [473251/2009-4, 301519/2008-0, 301867/2010-0]Conselho Nacional de Pesquisa e Desenvolvimento (CNPq