A case of acanthosis nigricans in a HIV-infected patient

Background: To date, very little information is available concerning the relationship between acanthosis nigricans (AN) and infection with human immunodeficiency virus type 1 (HIV-1). Case presentation: Herein, we report the case of a middle-aged man admitted for fever and progressively worsening dyspnea in the context of an opportunistic pneumonia and firstly diagnosed with acquired immunodeficiency syndrome (AIDS). At the time of diagnosis, physical examination revealed the presence of a palpable, hyperpigmented skin lesion on the left areola with surface desquamation and velvety texture consistent with AN. Of note, the most common primary etiologies related to AN were excluded and the complete regression of the skin lesion was observed once antiretroviral therapy was started. Conclusion: This is the second report of AN found in patients with AIDS and apparently responsive to prolonged antiretroviral treatment. Possible explanations of this association are still not completely understood, probably related to virus-induced changes in lipid metabolism. Our experience suggests that HIV testing should always be considered in the setting of apparently idiopathic AN

Position controlled self-catalyzed growth of GaAs nanowires by molecular beam epitaxy

GaAs nanowires are grown by molecular beam epitaxy using a self-catalyzed, Ga-assisted growth technique. Position control is achieved by nano-patterning a SiO2 layer with arrays of holes with a hole diameter of 85 nm and a hole pitch varying between 200 nm and 2 \mum. Gallium droplets form preferentially at the etched holes acting as catalyst for the nanowire growth. The nanowires have hexagonal cross-sections with {110} side facets and crystallize predominantly in zincblende. The interdistance dependence of the nanowire growth rate indicates a change of the III/V ratio towards As-rich conditions for large hole distances inhibiting NW growth.Comment: 9 pages, 4 figure

Structural and morphological TEM characterization of GaAs based nanowires

The question of a structural and morphological characterization of GaAs based nanowires is the research interest of this thesis. For this purpose standard and analytical transmission electron microscopy techniques were employed. New investigation methodologies are introduced in order to obtain a reliable interpretation of the results. The principal motivation on developing a new investigation method is the necessity to relate the results of crystal structure and morphology characterizations to microscopic and NW-specific parameters and not to macroscopic and general growth parameters. This allows a reliable comparison of NW characteristics and enhances the comprehension of their growth mechanism.The analysis of the results on crystal structure investigations, assuming this new perspective, delivers the fundamental finding that the axial growth of Au-assisted GaAs NWs can change in a pseudo Ga-assisted growth due to a non steady-state regime of the Ga accumulation process in the liquid droplet. The attempt to associate the observed crystal structures to one of these two growth modes reveals that zinc blende segments are most probably generated when a pseudo Ga-assisted growth occurs. This experimental evidence is in accordance with investigations developed by Glas et al. and Spirkoska et al. and with the current understanding of the NW growth mechanism and unifies the interpretation of catalytic growth of GaAs NWs. A Mn doped GaAs shell deposited at low temperature on core GaAs NWs is characterized for the first time. The growth is found to be epitaxial and to confer the quality of the core crystal to the shell crystal. As a consequence a high stacking fault density of the core NW limits the temperature of the shell growth due to the formation of clusters. Cross sections of (Ga,Mn)As shells are investigated. Simple kinetic and thermodynamical considerations lead to the conclusion of morphological instability of the low temperature radial growth. Analytical measurements on a shell cross section reveal the presence of Mn segregation effects and suggest, as a first interpretation, a higher diffusion coefficient on the (Ga,Mn)As wurtzite surfaces for Ga than for Mn adatoms

Transition from Au to pseudo-Ga catalyzed growth mode observed in GaAs nanowires grown by molecular beam epitaxy

We investigate the correlation between the Ga concentration of the catalyst droplet and the adopted crystal structure of individual GaAs nanowires grown by molecular-beam epitaxy using Au as a catalyst material. Through a postgrowth analysis the Ga content of the catalyst droplet during growth is estimated and related to the observed crystal structure of the nanowires. Depending on the Ga concentration, we observe a transition from typical Au catalyzed to pseudo-Ga assisted nanowire growth: Nanowires with low Ga concentration of the catalyst droplet during growth form predominantly wurtzite crystal structures. For Ga concentrations higher than 75 at. %, which we refer to as the pseudo-Ga assisted growth mode, the probability to form zinc-blende segments is strongly enhanced owing to the reduced droplet surface energy of the catalyst

Reorientation transition of the magnetic proximity polarization in Fe/(Ga,Mn)As bilayers

Recently, it has been observed that thin ferromagnetic Fe films deposited on top of (Ga,Mn)As layers induce a significant proximity polarization in the (Ga,Mn)As film even at room temperature. Furthermore, it was found that a thin interfacial region of the (Ga,Mn)As film is coupled antiferromagnetically to the Fe layer. Here we report a series of combined x-ray magnetic dichroism and superconducting quantum interference device magnetometer measurements for Fe/(Ga,Mn)As bilayers where the (Ga,Mn)As layer thickness is varied between 5 and 50 nm. We find a reorientation transition of the magnetic proximity polarization as a function of the (Ga,Mn)As thickness. The data are compared to results obtained performing ab initio calculations. A varying concentration of Mn interstitials as a function of (Ga,Mn)As layer thickness is responsible for this reorientation. Furthermore, exchange bias is studied in the fully epitaxial bilayer system. We find a rather strong ferromagnetic exchange bias. The strength of the exchange bias can be estimated by using a simple partial domain wall model

Hot electron spin attenuation lengths of bcc Fe34Co66—Room temperature Magnetocurrent of 1200%

We investigate spin-dependent hot electron transport through metallic epitaxial spin valves by ballistic electron magnetic microscopy (BEMM). By variation of the thickness of one of the ferromagnetic layers we determine the spin dependent attenuation lengths which reflect hot electron transport along the vicinity of the [1 0 0]-axis of the bcc Fe34Co66 lattice. The majority spin attenuation length is more than 6 times larger than that of the minority spins within the measured energy interval of 1.3 up to 2 eV above the Fermi level. Consequently a Magnetocurrent effect exceeding 1200% accompanied by a monotonic bias voltage behavior is observed at room temperature

A Single Step Preparation of Photothermally Active Polyvinylidene Fluoride Membranes Using Triethyl Phosphate as a Green Solvent for Distillation Applications

none5Membrane distillation is a growing technology that can address the growing problem of water shortage. The implementation of renewable energy and a reduction in the environmental impact of membrane production could improve the sustainability of this process. With this perspective, porous hydrophobic polyvinylidene fluoride (PVDF) membranes were prepared using triethyl phosphate (TEP) as a green solvent, using the non-solvent induced phase separation technique. Different amounts of carbon black were added to dope solutions to improve the photothermal properties of the membranes and to enable direct heating by solar energy. By optimizing the preparation conditions, membranes with porosity values as high as 87% were manufactured. Vacuum membrane distillation tests carried out using a concentrated NaCl solution at 50 °C showed distillate fluxes of up to 36 L/m2 h and a complete salt rejection. Some preliminary studies on the photothermal performance were also conducted and highlighted the possibility of using such membranes in a direct solar membrane distillation configuration.openMarcello Pagliero; Antonio Comite; Camilla Costa; Ilaria Rizzardi; Omar SodaPagliero, Marcello; Comite, Antonio; Costa, Camilla; Rizzardi, Ilaria; Soda, Oma

Coexistence of ferromagnetism and quantum Hall effect in Mn modulation-doped two-dimensional hole systems

Modulation doping using Mn as an acceptor has been applied to the molecular beam epitaxial grown compressively strained InAs channels. Strain engineering has been accomplished by the growth of a graded, fully relaxed InxAl1-xAs buffer layer on GaAs(0 0 1) substrates in which the In content x was increased from 0% to 75%. Transmission electron microscopical investigation of the heterostructures reveals the high quality of the heterostructures grown on top of the metamorphic buffer layer. Significant segregation and diffusion of the Mn doping profile is confirmed by secondary ion mass spectroscopical analysis. Both normal as well as inverted doped quantum well structures show pronounced Shubnikov-de Haas oscillations and quantum Hall effect plateaus. However, for the inverted heterostructures where a significant Mn concentration within the InAs channel can be detected, a strong resistance maximum at B=0 T accompanied by a hysteretic behaviour and reproducible resistance jumps indicative of ferromagnetic ordering is observed