Thermal transport in epitaxial Si1-x Ge x alloy nanowires with varying composition and morphology.

We report on structural, compositional, and thermal characterization of self-assembled in-plane epitaxial Si1-x Ge x alloy nanowires grown by molecular beam epitaxy on Si (001) substrates. The thermal properties were studied by means of scanning thermal microscopy (SThM), while the microstructural characteristics, the spatial distribution of the elemental composition of the alloy nanowires and the sample surface were investigated by transmission electron microscopy and energy dispersive x-ray microanalysis. We provide new insights regarding the morphology of the in-plane nanostructures, their size-dependent gradient chemical composition, and the formation of a 5 nm thick wetting layer on the Si substrate surface. In addition, we directly probe heat transfer between a heated scanning probe sensor and Si1-x Ge x alloy nanowires of different morphological characteristics and we quantify their thermal resistance variations. We correlate the variations of the thermal signal to the dependence of the heat spreading with the cross-sectional geometry of the nanowires using finite element method simulations. With this method we determine the thermal conductivity of the nanowires with values in the range of 2-3 W m-1 K-1. These results provide valuable information in growth processes and show the great capability of the SThM technique in ambient environment for nanoscale thermal studies, otherwise not possible using conventional techniques.

Nanoscale imaging of InN segregation and polymorphism in single vertically aligned InGaN/GaN multi quantum well nanorods by tip-enhanced Raman scattering.

Vertically aligned GaN nanorod arrays with nonpolar InGaN/GaN multi quantum wells (MQW) were grown by MOVPE on c-plane GaN-on-sapphire templates. The chemical and structural properties of single nanorods are optically investigated with a spatial resolution beyond the diffraction limit using tip-enhanced Raman spectroscopy (TERS). This enables the local mapping of variations in the chemical composition, charge distribution, and strain in the MQW region of the nanorods. Nanoscale fluctuations of the In content in the InGaN layer of a few percent can be identified and visualized with a lateral resolution below 35 nm. We obtain evidence for the presence of indium clustering and the formation of cubic inclusions in the wurtzite matrix near the QW layers. These results are directly confirmed by high-resolution TEM images, revealing the presence of stacking faults and different polymorphs close to the surface near the MQW region. The combination of TERS and HRTEM demonstrates the potential of this nanoscale near-field imaging technique, establishing TERS as a very potent, comprehensive, and nondestructive tool for the characterization and optimization of technologically relevant semiconductor nanostructures.

Probing local strain and composition in Ge nanowires by means of tip-enhanced Raman scattering.

Local strain and Ge content distribution in self-assembled, in-plane Ge/Si nanowires grown by combining molecular beam epitaxy and the metal-catalyst assisted-growth method were investigated by tip-enhanced Raman scattering. We show that this technique is essential to study variations of physical properties of single wires at the nanoscale, a task which cannot be achieved with conventional micro-Raman scattering. As two major findings, we report that (i) the Ge distribution in the (001) crystallographic direction is inhomogeneous, displaying a gradient with a higher Ge content close to the top surface, and (ii) in contrast, the (uncapped) wires exhibit essentially the same small residual compressive strain everywhere along the wire.

Titanium-assisted growth of silica nanowires: from surface-matched to free-standing morphologies.

We report on an oxide-assisted growth technique for silica nanowires which allows tuning the growth from surface-matched nanowires to free-standing morphologies based on growth control by Ti in the role of a catalyst and surfactant. Using an adjustable Ti concentration, we grew silica nanowires with lengths ranging from 100 nm up to several millimetres whose defect chemistry was analysed by electron microscopy tools, monochromatic cathodoluminescence imaging and time resolved photoluminescence spectroscopy. The knowledge of the luminescence properties and the related defect occurrence along with their spatial distribution is pivotal for advancing silica nanowire growth in order to realize successful device designs based on self-assembled Si/SiO(x) nanostructures. We demonstrate a core-shell structure of the grown nanowires with a highly luminescent 150 nm thick shell and outstandingly fast decaying dynamics (≈1 ns) for glass-like materials. The conjunction of the observed efficient and stable luminescences with their attributed decaying behaviours suggests applications for silica nanowires such as active and passive optical interconnectors and white light phosphors. The identification of a time domain difference for the spectral regime from 2.3 to 3.3 eV, within the confined spatial dimensions of a single nanowire, is very promising for future, e.g. data transmission applications, employing silica nanowires which exhibit achievable compatibility with commonly applied silicon-based electronics. A qualitative growth model based on silica particle diffusion and Ti-assisted seed formation is developed for the various types of segregated silica nanowires which extends commonly assumed oxide-assisted growth mechanisms.

On the assessment of hydroxyapatite fluoridation by means of Raman scattering.

Hydroxyapatite is the main mineral component of bones and teeth. Fluorapatite, a bioceramic that can be obtained from hydroxyapatite by chemical substitution of the hydroxide ions with fluoride, exhibits lower mineral solubility and larger mechanical strength. Despite the widespread use of fluoride against caries, a reliable technique for unambiguous assessment of fluoridation in in vitro tests is still lacking. Here we present a method to probe fluorapatite formation in fluoridated hydroxyapatite by combining Raman scattering with thermal annealing. In synthetic minerals, we found that effectively fluoride substituted hydroxyapatite transforms into fluorapatite only after heat treatment, due to the high activation energy for this first order phase transition.

Closing the Stability-Performance Gap in Organic Thermoelectrics by Adjusting the Partial to Integer Charge Transfer Ratio.

Two doping mechanisms are known for the well-studied materials poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), namely, integer charge transfer (ICT) and charge transfer complex (CTC) formation. Yet, there is poor understanding of the effect of doping mechanism on thermal stability and the thermoelectric properties. In this work, we present a method to finely adjust the ICT to CTC ratio. Using it, we characterize electrical and thermal conductivities as well as the Seebeck coefficient and the long-term stability under thermal stress of P3HT and PBTTT of different ICT/CTC ratios. We establish that doping through the CTC results in more stable, yet lower conductivity samples compared to ICT doped films. Importantly, moderate CTC fractions of ∼33% are found to improve the long-term stability without a significant sacrifice in electrical conductivity. Through visible and IR spectroscopies, polarized optical microscopy, and grazing-incidence wide-angle X-ray scattering, we find that the CTC dopant molecule access sites within the polymer network are less prone to dedoping upon thermal exposure.

Farming thermoelectric paper.

Waste heat to electricity conversion using thermoelectric generators is emerging as a key technology in the forthcoming energy scenario. Carbon-based composites could unleash the as yet untapped potential of thermoelectricity by combining the low cost, easy processability, and low thermal conductivity of biopolymers with the mechanical strength and good electrical properties of carbon nanotubes (CNTs). Here we use bacteria in environmentally friendly aqueous media to grow large area bacterial nanocellulose (BC) films with an embedded highly dispersed CNT network. The thick films (≈10 µm) exhibit tuneable transparency and colour, as well as low thermal and high electrical conductivity. Moreover, they are fully bendable, can conformally wrap around heat sources and are stable above 500 K, which expands the range of potential uses compared to typical conducting polymers and composites. The high porosity of the material facilitates effective n-type doping, enabling the fabrication of a thermoelectric module from farmed thermoelectric paper. Because of vertical phase separation of the CNTs in the BC composite, the grown films at the same time serve as both the active layer and separating layer, insulating each thermoelectric leg from the adjacent ones. Last but not least, the BC can be enzymatically decomposed, completely reclaiming the embedded CNTs.

[Tuberculosis in patients with HIV infection]. / Tuberculosis en pacientes infectados por el VIH.

Tuberculosis is a clear example of infection that requires cellular immunity for its control. The spread throughout the world of the Human Immunodeficiency Virus (HIV) resulted in its interaction with tuberculosis altering the descending curve of the latter disease in some developed countries, and brought an aggravation of the problem in other countries with few economic and health resources and where tuberculosis was endemic. HIV increases the risk of reactivation of latent tuberculosis infection and accelerates progression after infection or reinfection; on the other hand, TB aggravates the prognosis of patients infected with HIV. This article sets out the differential aspects in the clinical manifestations of TB amongst populations with and without HIV infection; we also comment on some special characteristics in the treatment of tuberculosis in HIV patients. With the exception of primary cutaneous infections produced by accidental inoculation and infantile lymphadenitis, the majority of the cases of disease due to non-tuberculosis mycobacteria (NTM) affect patients with certain predisposing factors. In the case of patients with AIDS, the deep immunological disorder provoked by HIV brings a particular susceptibility to suffering invasive disease due to certain NTM, principally M. avium complex and M. kansasii.

[Primary pyomyositis caused by Streptococcus intermedius]. / Piomiositis primaria causada por Streptococcus intermedius.

Pyomyositis is a sub-acute bacterial infection that affects the striated muscle and is usually accompanied by the formation of an abscess in this muscle. It was initially described as an endemic disease in the tropics and only in recent years has an increase been observed in the number of cases in countries with a temperate climate in relation to an increase of immuno-depressed patients. The causal germ is Staphylococcus aureus in more than 75% of cases. The most useful imaging test is magnetic resonance. Treatment consists of complete surgical draining of the abscess combined with a suitable antibiotic therapy. We present a case of primary pyomyositis of the quadriceps in a diabetic patient with a remote traumatic antecedent of the affected zone and caused by an unusual germ. A complete recovery was obtained, without sequels, following surgical draining and 4 weeks of endovenous antibiotic treatment.

[Fever, pleural effusion and osteolytic lesion in a patient with HIV infection]. / Fiebre, derrame pleural y lesión osteolítica en paciente con infección por VIH.

We present the case of a 28 year old patient who came for consultation on a fever of up to 40.8 degrees C, pleuritic pain on the right side and the appearance of a painful mass in the lower left extremity of four days evolution. Computerised axial tomography (CAT) showed the existence of a condensation in the middle lobe of the right lung with associated pleural effusion and bilateral miliary pattern. The echographic study of the lower left extremity showed a mass of soft parts with a cystic aspect with destruction of the cortical of the fibula and osseous destruction. Magnetic resonance confirmed the presence of osteomyelitis in the left fibula and of an abscess; Mycobacterium tuberculosis was also isolated in three samples of sputum that led to a diagnosis of disseminated tuberculosis with miliary lung affectation, peroneous osteomyelitis and tuberculous abscess of the soft parts. Anti-tuberculosis treatment was started (riphampicine, isoniacide and pirazinamide) followed, two weeks later, with antiretroviral treatment (AZT, 3TC and NVP). The patient developed a clinical picture of generalised cutaneous eruption that disappeared following the replacement of the riphampicine by etambutol. Due to the persistence of the mass of soft parts following five weeks of anti-tuberculosis treatment, we proceeded to surgical draining of the abscess. The subsequent evolution was favourable, with the patient remaining asymptomatic one month after hospital discharge.

[Effectiveness of second-generation direct-acting antivirals in chronic hepatitis C]. / Efectividad de los antivirales de acción directa de segunda generación en el tratamiento de la hepatitis C crónica.

BACKGROUND: Second-generation direct-acting antivirals (DAA) have shown high sustained virologic response (SVR) for the treatment of chronic hepatitis C in clinical trials. The objective of this study is to estimate DAA effectiveness in treatment of this disease. METHODS: Hepatitis C virus (HCV) monoinfected patients and HCV-human immunodeficiency virus (HIV) coinfected pa-tients who started interferon-free DAA based regimens during 2015 were included. The primary effectiveness outcome was SVR, defined as an undetectable viral load 12 weeks after the end of treatment. RESULTS: A total of 293 patients were enrolled, and 52 (17.7%) were HIV coinfected. HCV 1b genotype was the most prevalent in monoinfected patients (41.5%) and 1a in HIV coinfected patients (40.4%). The proportion of cirrhosis was higher among HIV coinfected patients (69.2% vs 41.1%; p<0.0001), mostly Child-Pugh A. SVR was achieved by 96.9% of patients (284/293), in an intention-to-treat analysis (CI 95%: 94.9-98.9), in which just 4 people had virologic failure. Both naïve and pretreated patients had SVR higher than 95%, and in most of subgroups, according to the presence of cirrhosis, HIV coinfection and HVC genotype, effectiveness rates were near or above 90%. CONCLUSIONS: DAA are highly effective, with similar or higher rates of SVR than that found in clinical trials, and even among difficult to treat populations.

Thermal conductivity and air-mediated losses in periodic porous silicon membranes at high temperatures.

Heat conduction in silicon can be effectively engineered by means of sub-micrometre porous thin free-standing membranes. Tunable thermal properties make these structures good candidates for integrated heat management units such as waste heat recovery, rectification or efficient heat dissipation. However, possible applications require detailed thermal characterisation at high temperatures which, up to now, has been an experimental challenge. In this work we use the contactless two-laser Raman thermometry to study heat dissipation in periodic porous membranes at high temperatures via lattice conduction and air-mediated losses. We find the reduction of the thermal conductivity and its temperature dependence closely correlated with the structure feature size. On the basis of two-phonon Raman spectra, we attribute this behaviour to diffuse (incoherent) phonon-boundary scattering. Furthermore, we investigate and quantify the heat dissipation via natural air-mediated cooling, which can be tuned by engineering the porosity.Nanostructuring of silicon allows acoustic phonon engineering, but the mechanism of related thermal transport in these structures is not fully understood. Here, the authors study the heat dissipation in silicon membranes with periodic nanoholes and show the importance of incoherent scattering.

Tuning thermal transport in ultrathin silicon membranes by surface nanoscale engineering.

A detailed understanding of the connections of fabrication and processing to structural and thermal properties of low-dimensional nanostructures is essential to design materials and devices for phononics, nanoscale thermal management, and thermoelectric applications. Silicon provides an ideal platform to study the relations between structure and heat transport since its thermal conductivity can be tuned over 2 orders of magnitude by nanostructuring. Combining realistic atomistic modeling and experiments, we unravel the origin of the thermal conductivity reduction in ultrathin suspended silicon membranes, down to a thickness of 4 nm. Heat transport is mostly controlled by surface scattering: rough layers of native oxide at surfaces limit the mean free path of thermal phonons below 100 nm. Removing the oxide layers by chemical processing allows us to tune the thermal conductivity over 1 order of magnitude. Our results guide materials design for future phononic applications, setting the length scale at which nanostructuring affects thermal phonons most effectively.

Infection of a pacemaker by Brucella melitensis.

We report a case that, to the best of our knowledge, is the only published instance of infection of a pacemaker and its leads by Brucella melitensis. Furthermore, this case suggests that B. melitensis may be able to persist around pacemaker devices despite its having been eliminated from the rest of the body. The patient was a sheep shearer who had just undergone a 45-day course of antibiotic therapy for brucella and had been considered cured on the basis of negative blood cultures.

[Bacterial infections in patients infected by HIV]. / Infecciones bacterianas en pacientes infectados por el VIH.

Individuals infected by the human immuno deficiency are more prone to suffering certain bacterial infections in the course of their clinical evolution. The agents involved in these infections are: Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, Salmonella spp and Campylobacter spp, which occasion an increase in morbidity and mortality. With a lower frequency, but with an equal morbidity and mortality, infections have been found caused by Rhodococcus equi, Nocardia spp and Bartonella spp. Even though all of them account for a selective impairment of immunodeficiency in one way or another, their incidence varies. Other factors such as degree of immuno suppression, habits, social and geographic living environment could be important. In general, there is a lack of chemoprophylactic strategies for their prevention. Early diagnosis and correct treatment could have important advantages for the quality of life and survival of these patients

[Disseminated Mycobacterium africanum infection]. / Infección diseminada por Mycobacterium africanum.

A case of disseminated Mycobacterium africanum infection in a 28 years old black male with no known causes of immunosuppression and resident in Spain 2 years prior to his symptomatology is described. In addition, the characteristics of Mycobacterium africanum and its capacity to produce pathology in man are discussed as is its proper treatment leading to satisfactory cure.

A novel contactless technique for thermal field mapping and thermal conductivity determination: two-laser Raman thermometry.

We present a novel contactless technique for thermal conductivity determination and thermal field mapping based on creating a thermal distribution of phonons using a heating laser, while a second laser probes the local temperature through the spectral position of a Raman active mode. The spatial resolution can be as small as 300 nm, whereas its temperature accuracy is ±2 K. We validate this technique investigating the thermal properties of three free-standing single crystalline Si membranes with thickness of 250, 1000, and 2000 nm. We show that for two-dimensional materials such as free-standing membranes or thin films, and for small temperature gradients, the thermal field decays as T(r) ∝ ln(r) in the diffusive limit. The case of large temperature gradients within the membranes leads to an exponential decay of the thermal field, T ∝ exp[ - A·ln(r)]. The results demonstrate the full potential of this new contactless method for quantitative determination of thermal properties. The range of materials to which this method is applicable reaches far beyond the here demonstrated case of Si, as the only requirement is the presence of a Raman active mode.

Poly(anhydride) nanoparticles act as active Th1 adjuvants through Toll-like receptor exploitation.

The mechanisms that underlie the potent Th1-adjuvant capacity of poly(methyl vinyl ether-co-maleic anhydride) nanoparticles (NPs) were investigated. Traditionally, polymer NPs have been considered delivery systems that promote a closer interaction between antigen and antigen-presenting cells (APCs). Our results revealed that poly(anhydride) NPs also act as agonists of various Toll-like receptors (TLRs) (TLR2, -4, and -5), triggering a Th1-profile cytokine release (gamma interferon [IFN-gamma], 478 pg/ml versus 39.6 pg/ml from negative control; interleukin-12 [IL-12], 40 pg/ml versus 7.2 pg/ml from negative control) and, after incubation with dendritic cells, inducing a 2.5- to 3.5-fold increase of CD54 and CD86 costimulatory molecule expression. Furthermore, in vivo studies suggest that NPs actively elicit a CD8(+) T-cell response. Immunization with empty NPs resulted in a significant delay in the mean survival date (from day 7 until day 23 postchallenge) and a protection level of 30% after challenge against a lethal dose of Salmonella enterica serovar Enteritidis. Taken together, our results provide a better understanding of how NPs act as active Th1 adjuvants in immunoprophylaxis and immunotherapy through TLR exploitation.

A polysaccharide from the human commensal Bacteroides fragilis protects against CNS demyelinating disease.

The intestinal microbiome may have a critical roll in susceptibility or resistance to immune-mediated diseases. Alterations of the gut microflora after oral antibiotic treatment can regulate encephalomyelitis (EAE), an animal model for human multiple sclerosis (MS). We now show that a zwitterionic capsular polysaccharide A (PSA) of Bacteroides fragilis can protect against central nervous system demyelinating disease. Oral administration with purified PSA protected mice against EAE prophylactic and therapeutically. PSA treatment enhanced CD103 expressing dendritic cells (DCs) that accumulated in the cervical lymph nodes. Exposure of naïve DCs to PSA induced the conversion of naïve CD4(+) T cells into interleukin (IL)-10-producing FoxP3(+)Treg cells. Protection against EAE was completely abrogated in IL-10-deficient mice. Our results show an important role for a molecule from human commensal bacteria in protecting against EAE and suggest the possibility for protection in MS.