Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals.

A new analytical expression for the size-dependent bandgap of colloidal semiconductor nanocrystals is proposed within the framework of the finite-depth square-well effective mass approximation in order to provide a quantitative description of the quantum confinement effect. This allows one to convert optical spectroscopic data (photoluminescence spectrum and absorbance edge) into accurate estimates for the particle size distributions of colloidal systems even if the traditional effective mass model is expected to fail, which occurs typically for very small particles belonging to the so-called strong confinement limit. By applying the reported theoretical methodologies to CdTe nanocrystals synthesized through wet chemical routes, size distributions are inferred and compared directly to those obtained from atomic force microscopy and transmission electron microscopy. This analysis can be used as a complementary tool for the characterization of nanocrystal samples of many other systems such as the II-VI and III-V semiconductor materials.

[Lung diffusion capacity and quality of life 6 months after discharge from the ICU among survivors of acute respiratory distress syndrome due to influenza A H1N1]. / Capacidad de difusión pulmonar y calidad de vida a los 6 meses del alta de la unidad de cuidados intensivos en sobrevivientes a síndrome de distrés respiratorio agudo por influenza A H1N1.

OBJECTIVE: An evaluation is made of lung function and quality of life 6 months after discharge from the Intensive Care Unit (ICU) among survivors of acute respiratory distress syndrome (ARDS) due to pandemic 2009 influenza A H1N1, based on studies of lung function and the EQ-5D health questionnaire. DESIGN: Case series. SETTING: The ICU of Dr. Leónidas Lucero Acute Cases Municipal Hospital, Bahía Blanca, Argentina. PATIENTS: PATIENTS discharged from the ICU who had been admitted with ARDS in 2009 due to influenza A H1N1. RESULTS: Eleven patients were studied. Seven were positive for influenza H1N1 and four were negative. The mean age was 37±9.5 years, and 73% were males. Quality of life, as measured by the EQ-5D, showed changes in the 5 components in all patients, particularly in the pain/discomfort dimension 1.55±0.52; health status (EQ%health) was 70%±24. The indices adjusted for Argentina were Time Trade Off (TTO) 0.903±0.085 and Visual Analog Scale (VAS) 0.827±0.153. In all patients, spirometry and the study of pulmonary diffusion (DLCO) showed values of >80%. There was no correlation between lung diffusion and quality of life (%DLCO and EQ%health). A correlation was observed between quality of life and TTO (EQ%health and TTO), and between quality of life and the VAS score (EQ%health and VAS). CONCLUSION: Although the sample is small, our results suggest that patients with ARDS due to influenza A H1N1 evaluated 6 months after discharge from the ICU show no deterioration of lung function, and the impact on quality of life is moderate-in contrast to the situation found in patients with ARDS of other etiologies.

Intrinsic stability of the smallest possible silver nanotube.

Recently, Lagos et al. [Nature Nanotech. 4, 149 (2009)] reported the discovery of the smallest possible Ag nanotube with a square cross section. Ab initio density functional theory calculations strongly support that the stability of these hollow structures is structurally intrinsic and not the result of contamination by light atoms. We also report the first experimental observation of the theoretically predicted corrugation of the hollow structure. Quantum conductance calculations predict a unique signature of 3.6 G0 for this new family of nanotubes.

Langerhans' cell count and HLA class II profile in cervical intraepithelial neoplasia in the presence or absence of HIV infection.

OBJECTIVES: The progression of immunosuppression in human immunodeficiency virus (HIV)+ women has been correlated with elevated incidence of squamous intraepithelial lesions (SIL), probably indicating the role of local immune milieu. In this study, we analysed S100, and HLA class II molecule expression in cervical biopsies according to HIV status, to the severity of SIL and to human papillomavirus (HPV) type. METHODS: Biopsies from 34 HIV+ and 44 HIV- patients with normal cervix or low- or high-grade SIL were studied. Langerhans' cells (LC) (S100), HLA class II and HLA-DQ molecules were evaluated by immunohistochemistry. HPV detection was performed using polymerase chain reaction (PCR). For statistical analysis Mann-Whitney (P< or =0.05) and Spearman test were used. RESULTS: Epithelial S100 and HLA class II density were significantly increased with the severity of lesion (P=0.032; P=0.005). Epithelial S100+ increased in HPV+ (P=0.038), and HLA class II density decreased in HPV 16+ (P=0.035) or 18+ (P<0.0001) samples. HIV infection was associated with increased stromal S100+ (P=0.0005) and decreased HLA class II densities (P=0.0001). Decreased stromal S100+ was observed in women with CD4<500 cells/microl (P=0.050). Among HIV+ patients with SIL, the lowest S100 and epithelial HLA class II densities were detected in women with CD4<200 cells/microl (P=0.045). CONCLUSIONS: After the establishment of AIDS, increased numbers of immature LCs and a reduction in HLA class II occurred, possibly turning the cervical milieu more favourable to HPV persistence. HPV 16 and 18 infections may interfere with the antigen presenting activity, possibly as an evasion mechanism.

Observation of the smallest metal nanotube with a square cross-section.

Understanding the mechanical properties of nanoscale systems requires a range of measurement techniques and theoretical approaches to gather the relevant physical and chemical information. The arrangements of atoms in nanostructures and macroscopic matter can be different, principally due to the role of surface energy, but the interplay between atomic and electronic structure in association with applied mechanical stress can also lead to surprising differences. For example, metastable structures such as suspended chains of atoms and helical wires have been produced by stretching metal junctions. Here, we report the spontaneous formation of the smallest possible metal nanotube with a square cross-section during the elongation of silver nanocontacts. Ab initio calculations and molecular simulations indicate that the hollow wire forms because this configuration allows the surface energy to be minimized, and also generates a soft structure capable of absorbing a huge tensile deformation.

Designing spatial correlation of quantum dots: towards self-assembled three-dimensional structures.

Buried two-dimensional arrays of InP dots were used as a template for the lateral ordering of self-assembled quantum dots. The template strain field can laterally organize compressive (InAs) as well as tensile (GaP) self-assembled nanostructures in a highly ordered square lattice. High-resolution transmission electron microscopy measurements show that the InAs dots are vertically correlated to the InP template, while the GaP dots are vertically anti-correlated, nucleating in the position between two buried InP dots. Finite InP dot size effects are observed to originate InAs clustering but do not affect GaP dot nucleation. The possibility of bilayer formation with different vertical correlations suggests a new path for obtaining three-dimensional pseudocrystals.

Experimental realization of suspended atomic chains composed of different atomic species.

Research into nanostructured materials frequently relates to pure substances. This contrasts with industrial applications, where chemical doping or alloying is often used to enhance the electrical or mechanical properties of materials. However, the controlled preparation of doped nanomaterials has been much more difficult than expected because the increased surface-area-to-volume ratio can, for instance, lead to the expulsion of impurities (self-purification). For nanostructured alloys, the influence of growth methods and the atomic structure on self-purification is still open to investigation. Here, we explore, experimentally and with molecular dynamics simulations, to what extent alloying persists in the limit that a binary metal is mechanically stretched to a linear chain of atoms. Our results reveal a gradual evolution of the arrangement of the different atomic elements in the narrowest region of the chain, where impurities may be expelled to the surface or enclosed during elongation.

Association of tumor necrosis factor a-2 and a-8 microsatellite alleles with human papillomavirus and squamous intraepithelial lesions among women in Brazil.

Infection with oncogenic human papillomavirus (HPV) is considered to be the major risk factor for cervical cancer. Tumor necrosis factor (TNF) is a pluripotent cytokine that plays an important role in inhibiting the action of microbial agents, and TNF microsatellite polymorphisms have been associated with several diseases, including cancer and viral infections. This study analyzed the associations between TNFa to -e microsatellite polymorphisms and the severity of squamous intraepithelial lesions (SIL), according to the presence of the oncogenic HPV16 and HPV18 types. Samples from 146 HPV-positive women with low-grade SIL (LSIL) and high-grade SIL (HSIL) and samples from 101 healthy women were studied. TNF microsatellite polymorphism typing and HPV detection and typing were performed using PCR-amplified DNA hybridized with sequence-specific primers. Data were analyzed by Fisher's exact test using the GENEPOP software. Significant associations were observed between LSIL and the TNFa-8 allele (4/166; P = 0.04), as well as between TNFa-2 with HPV18 only (16/44; P = 0.002) and TNFa-2 with HPV18 coinfection with HPV16 (16/44; P = 0.001). Patients exhibiting the TNFa-2 allele and harboring HPV18, in the presence or absence of coinfection with HPV16, had an increased risk of HSIL occurrence (13/38; P = 0.04; 5/10; P = 0.04) compared to patients with other HPV types. These results suggest that the TNFa-8 allele is associated with increased susceptibility to the occurrence of LSIL and that despite the presence of a high TNF-alpha production allele, the ability of HPV18 to resist the inhibitory effects of TNF-alpha may contribute to the occurrence of infection and consequently to HSIL in women with cervical HPV18 infection.

Doppler-free continuous-wave phase-conjugate spectrum of SF6 by resonant degenerate four-wave mixing at 10.6 microm.

A phase-conjugate signal has been obtained in SF(6) with a peak reflectivity of 1.2 x 10(-3) by using a cw CO(2) laser operating on the P(16) line. The degenerate four-wave mixing spectrum exhibits a Doppler-free structure with 2-MHz resolution. When the reflectivity spectrum is compared with the saturated-absorption spectrum, matching peaks in the reflectivity spectrum are found over an 80-MHz bandwidth.

Indication of unusual pentagonal structures in atomic-size Cu nanowires.

We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of approximately 0.45 nm and approximately 4.5 conductance quanta.