Prevalence and impact of asthma among school-aged students in Lima, Peru.

SETTING AND OBJECTIVE: The International Study of Asthma and Allergies in Childhood (ISAAC) reported asthma prevalence in Peru to be among the highest in the world. We assessed the prevalence and morbidity of self-reported asthma in an underserved, peri-urban area of Lima, Peru, with limited medical access. DESIGN: The study was conducted in the outskirts of Lima from March to May 2011. Five hundred children aged 6-18 years were selected through cluster sampling. Parents completed a modified version of the ISAAC questionnaire. Children underwent spirometry testing. Those with a forced expiratory volume in one second (FEV1% predicted) 80% were tested for reversibility using salbutamol. RESULTS: Of the 500 children selected, 71% participated. The prevalence of asthma was 16.7%. Asthma symptoms were associated with self-reported asthma (P < 0.001); 52.5% of children with asthma had ever used an inhaler (P < 0.001), and 27.1% had never been to the doctor for respiratory problems (P < 0.001). CONCLUSION: We found a high prevalence of self-reported asthma and high morbidity related to asthma symptoms in the previous 12 months among the study cohort. Symptoms were poorly controlled due to limited availability of medication and access to medical services.

Reversible resistance modulation in mesoscopic silver wires induced by exposure to amine vapor.

Ensembles of silver nanowires (AgNEs) with diameters ranging from 200 nm to 1.0 microm have been prepared by electrochemical step edge decoration. These AgNEs showed a rapid (< 5 s), reversible increase in resistance upon exposure to the vapor of ammonia, trimethylamine, and pyridine. The amplitude of the resistance change was up to +3000% (DeltaR/Ro)-more than 2 orders of magnitude larger than can be explained based on boundary layer scattering effects. We experimentally probe the mechanism for this resistance modulation in the case of ammonia, and we propose a model to describe it. Conductive tip atomic force microscopy was used to probe individual sections of nanowires in AgNEs; these data revealed that the resistance change caused by NH(3) exposure was concentrated within a minority (approximately 10%) of the 5-microm wire segments that were probed--not uniformly distributed along each nanowire. All AgNEs showed a temperature dependence of their resistance, alpha, that was smaller than expected for silver metal. Highly sensitive AgNEs sometimes showed a negative alpha, characteristic of semiconductors, but negative alpha values were never observed for AgNEs with a low sensitivity to NH3. AgNEs did not respond to hydrocarbons, O2, H2O, N2, CO, or Ar, but a large (DeltaR/Ro > |-50%|) irreversible decrease in resistance was seen upon exposures to acids including HCl, HNO3, and H2SO4. Based on these and other data, we propose a model in which oxidized constrictions in silver nanowires limit the conductivity of the wire and provide a means for "gating" conduction based on the protonation state of the oxide surface.

Molybdenum disulfide nanowires and nanoribbons by electrochemical/chemical synthesis.

Molybdenum disulfide nanowires and nanoribbons have been synthesized by a two-step, electrochemical/chemical synthetic method. In the first step, MoO(x) wires (a mixture of MoO(2) and MoO(3)) were electrodeposited size-selectively by electrochemical step-edge decoration on a highly oriented pyrolytic graphite (HOPG) surface. Then, MoO(x) precursor wires were converted to MoS(2) by exposure to H(2)S either at 500-700 degrees C, producing "low-temperature" or LT MoS(2) nanowires that were predominantly 2H phase, or above 800 degrees C producing "high-temperature" or HT MoS(2) ribbons that were predominantly 3R phase. The majority of these MoS(2) wires and ribbons were more than 50 microm in length and were organized into parallel arrays containing hundreds of wires or ribbons. MoS(2) nanostructures were characterized by X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, selected area electron diffraction, X-ray diffraction, UV-visible absorption spectrometry, and Raman spectroscopy. HT and LT MoS(2) nanowires were structurally distinct: LT MoS(2) wires were hemicylindrical in shape and nearly identical in diameter to the MoO(x) precursor wires from which they were derived. LT MoS(2) wires were polycrystalline, and the internal structure consisted of many interwoven, multilayer strands of MoS(2); HT MoS(2) ribbons were 50-800 nm in width and 3-100 nm thick, composed of planar crystallites of 3R-MoS(2). These layers grew in van der Waals contact with the HOPG surface so that the c-axis of the 3R-MoS(2) unit cell was oriented perpendicular to the plane of the graphite surface. Arrays of MoS(2) wires and ribbons could be cleanly separated from the HOPG surface and transferred to glass for electrical and optical characterization. Optical absorption measurements of HT MoS(2) nanoribbons reveal a direct gap near 1.95 eV and two exciton peaks, A1 and B1, characteristic of 3R-MoS(2). These exciton peaks shifted to higher energy by up to 80 meV as the wire thickness was decreased to 7 nm (eleven MoS(2) layers). The energy shifts were proportional to 1/ L( parallel)(2), and the effective masses were calculated. Current versus voltage curves for both LT and HT MoS(2) nanostructures were probed as a function of temperature from -33 degrees C to 47 degrees C. Conduction was ohmic and mainly governed by the grain boundaries residing along the wires. The thermal activation barrier was found to be related to the degree of order of the crystallites and can be tuned from 126 meV for LT nanowires to 26 meV for HT nanoribbons.

Multimode detection of hydrogen gas using palladium-covered silicon micro-channels.

Palladium was electrodeposited onto lithographically patterned Si(100) "micro-channels" with dimensions of 2 microm (width) x 100 microm (length). The properties of these Pd-covered Si micro-channels for detecting dihydrogen gas were then evaluated. Pd electrodeposition was carried out under conditions favoring an instantaneous nucleation and growth mechanism. This strategy produced size-similar Pd particles at a coverage of (4-6) x 10(9) cm(-2) within the confines of the Si micro-channel. When the mean particle radius, ro, was smaller than a critical value (ro < rc = 70-85 nm), each Pd particle was well separated on the surface from adjacent particles, on average, and no response to H2 gas attributable to the micro-channel was observed. As Pd particles were grown larger, to a mean radius of ro approximately equal to rc, adjacent particles on the surface touched and the electrical resistance of the micro-channel dropped by several orders of magnitude. These "type 2" H2 sensors exhibited a rapid (< 1 s), reversible decrease in their resistance in response to exposure to H2 above 0.5%, but a minimum resistance was observed at 1-2%, and a resistance increase was seen at higher H2 concentration. This complex behavior resulted from the existence of three mechanisms for charge transport across the micro-channel. If still larger quantities of Pd were deposited, the Pd particle ensemble coalesced into an electrically continuous film. These "type 3" sensors became more resistive in the presence of H2, not more conductive as seen for sensors of types 1 and 2, but the amplitude of this response was smaller than seen for type 2 sensors.

Palladium mesowire arrays for fast hydrogen sensors and hydrogen-actuated switches.

Arrays of mesoscopic palladium wires prepared by electrodeposition form the basis for hydrogen sensors and hydrogen-actuated switches that exhibit a response time ranging from 20 ms to 5 s, depending on the hydrogen concentration. These devices were constructed by electrodepositing palladium mesowires on a highly oriented pyrolytic graphite surface and then transferring these mesowires to a cyanoacrylate film supported on a glass slide. The application of silver contacts to the ends of 10-100 mesowires, arrayed electrically in parallel, produced sensors and switches that exhibited a high conductivity state in the presence of hydrogen and a low conductivity state in the absence of hydrogen. After an initial exposure to hydrogen, 15-50 nanoscopic gaps are formed in each mesowire. These nanoscopic gaps or "break junctions" close in the presence of hydrogen gas and reopen in its absence as hydrogen is reversibly occluded by the palladium grains in each wire, and the palladium lattice expands and contracts by several percent. The change in resistance for sensors and switches was related to the hydrogen concentration over a range from 1 to 10%.

Hydrogen sensors and switches from electrodeposited palladium mesowire arrays.

Hydrogen sensors and hydrogen-activated switches were fabricated from arrays of mesoscopic palladium wires. These palladium "mesowire" arrays were prepared by electrodeposition onto graphite surfaces and were transferred onto a cyanoacrylate film. Exposure to hydrogen gas caused a rapid (less than 75 milliseconds) reversible decrease in the resistance of the array that correlated with the hydrogen concentration over a range from 2 to 10%. The sensor response appears to involve the closing of nanoscopic gaps or "break junctions" in wires caused by the dilation of palladium grains undergoing hydrogen absorption. Wire arrays in which all wires possessed nanoscopic gaps reverted to open circuits in the absence of hydrogen gas.

The utility of skin biopsies in pediatric cancer patients: a single-institution, retrospective review.

Medical records of all patients who were diagnosed with a malignancy and who underwent a skin biopsy were reviewed to determine the clinical utility of skin biopsies in this population. Skill biopsies resulted in a change or refinement of the prebiopsy diagnosis in 44% of patients undergoing an initial evaluation for a malignancy, 57% of patients on therapy, and 17% of patients off therapy. Skin biopsies led to a change in therapy in 26%, 34%, and 17% of each respective group. Overall, the skin biopsy changed or refined the prebiopsy diagnosis in 45% of cases and altered therapy in 38%. Skin biopsy is a clinically useful tool in pediatric oncology patients for the evaluation of cutaneous findings that elude diagnosis by visual inspection.