RESUMO

The martian surface has been continuously exposed to galactic cosmic radiation. Since organic compounds are degraded by ionizing radiation, knowledge of their decay constants is fundamental to predicting their stability on the martian surface. In this study, we report the radiolysis constant for the destruction of soil organic compounds at a starting concentration of ∼2011 µg C/gsoil from the Mojave Desert. The soils were exposed to gamma irradiation with absorbed doses of up to 19 MGy at room temperature, representing ∼250 million years of exposure to galactic cosmic rays. The destruction of total soil organic carbon and the formation of gases were investigated by a sequential on-line analytical array coupled to gas chromatography-mass spectrometry. Soil inorganic and organic carbon were degraded exponentially with a radiolysis constant 0.3 MGy-1(30%) producing mostly carbon dioxide (93.2%), carbon monoxide (6.2%), and methane (0.6%). Using the dose rate measured by the Radiation Assessment Detector on board the Curiosity rover, we make predictions on the survival of organic compounds in the cold martian subsurface. It is estimated that soil organic compounds with initial concentrations as those found today at the Mojave Desert would have been destroyed to levels <1 ppb at 0.1 m in depth in ∼2000 Myr. Pristine organic compounds are expected to be present at a depth of ∼1.5 m. These results are relevant for the search of organic compounds in past, present, and future missions to Mars. In particular, we predict that the upcoming ExoMars will encounter pristine organic compounds at this depth.

Assuntos

RESUMO

Nitrates and perchlorates are present both on Earth and Mars. In the Martian environment perchlorates dominate over nitrates whereas on Earth is contrariwise. This implies that the mechanisms responsible for their formation are different for both planets. The chemical elements required for their formation are nitrogen and chlorine, which are present in the atmosphere and surface, respectively. Dust in the Martian atmosphere causes atmospheric perturbations that lead to the development of dust-devils and sandstorms. Dust devils contain both chemical elements simultaneously, and normally generate high electric fields that can trigger the formation of electric discharges. Here we present laboratory experiments of this phenomenon using laser ablation of a sodium chloride (NaCl) plate in two different simulated atmospheres: (1) 96% CO2, 2% N2 and 2% Ar; and (2) 66% CO2, 33% N2 and 1% Ar. The dust that condensed and accumulated on the walls of the reactor was analyzed by different analytical techniques that included Fourier transform infrared spectroscopy, visible spectroscopy using azo dyes, thermogravimetry/simultaneous thermal analyses coupled to mass spectrometry, powder X-ray diffraction, and ion chromatography. The main components of the ablated dust corresponded to NaCl ≥ 91.5%, sodium nitrate (NaNO3 = 1.6-6.0%), and sodium perchlorate (NaClO4 âˆ¼ 0.2-0.3%). It is interesting to note that these salts formed in a dry process that is relevant to Mars today. A thermochemical model was used to understand the chemical steps that led to the formation of these salts in the gas phase. The NaNO3NaClO4 (wt/wt) ratio of this process was estimated to vary from 5.0 to 30.0; this ratio is too high compared to that found on Mars (NO3-ClO4- (wt/wt)) from 0.004 to 0.13). This implies that gaseous NaCl was not efficiently oxidized to perchlorate by the electric discharge process. We propose instead that gaseous metal chlorides (e.g., MgCl2, NaCl, CaCl2, KCl) were supplied to the atmosphere by the volatilization of chloride minerals present in the dust by electric discharges generated in dust devils and were subsequently oxidized to perchlorate by photochemical processes. Further work is required to assess the relative contribution of this possible source.

Assuntos

Assuntos

Assuntos

RESUMO

Increased border enforcement efforts have redistributed unauthorized Mexican migration to the United States (US) away from traditional points of crossing, such as San Diego and El Paso, and into more remote areas along the US-Mexico border, including southern Arizona. Yet relatively little quantitative scholarly work exists examining Mexican migrants' crossing, apprehension, and repatriation experiences in southern Arizona. We contend that if scholars truly want to understand the experiences of unauthorized migrants in transit, such migrants should be interviewed either at the border after being removed from the US, or during their trajectories across the border, or both. This paper provides a methodological overview of the Migrant Border Crossing Study (MBCS), a unique data source on Mexican migrants who attempted an unauthorized crossing along the Sonora-Arizona border, were apprehended, and repatriated to Nogales, Sonora in 2007-09. We also discuss substantive and theoretical contributions of the MBCS.

Assuntos

RESUMO

El Lupus Eritematoso Sistémico (LES) es una enfermedad autoinmune, multisistémica, episódica que puede llegar a ser fatal. Su sintomatología variable y presentaciones atípicas hacen de esta patología un reto diagnóstico.Se reporta el caso de una paciente mujer de 31 años con antecedente de teratoma de ovario, que refiere desde hace 9 meses la sensación de plentud epigástrica y distensión abdominal compatible con ascitis, acompañada de baja ponderal de peso. El diagnóstico riguroso que incluyó pruebas de laboratorio, de imagen y de líquido ascítico, descartó la etiología neoplásica; llegando a concluir que LES era la causa de estas manifestaciones. Debido a la demora en el diagnóstico y pese a que se inició tratamiento esteroideo, la presentación de una respuesta desfavorable al tratamiento y una infección intercurrente influyó en el desenlace fatal, lo que nos hace considerar la presentación de este caso.

Assuntos

Assuntos

RESUMO

The failure of Viking Lander thermal volatilization (TV) (without or with thermal degradation)-gas chromatography (GC)-MS experiments to detect organics suggests chemical rather than biological interpretations for the reactivity of the martian soil. Here, we report that TV-GC-MS may be blind to low levels of organics on Mars. A comparison between TV-GC-MS and total organics has been conducted for a variety of Mars analog soils. In the Antarctic Dry Valleys and the Atacama and Libyan Deserts we find 10-90 mug of refractory or graphitic carbon per gram of soil, which would have been undetectable by the Viking TV-GC-MS. In iron-containing soils (jarosites from Rio Tinto and Panoche Valley) and the Mars simulant (palogonite), oxidation of the organic material to carbon dioxide (CO(2)) by iron oxides and/or their salts drastically attenuates the detection of organics. The release of 50-700 ppm of CO(2) by TV-GC-MS in the Viking analysis may indicate that an oxidation of organic material took place. Therefore, the martian surface could have several orders of magnitude more organics than the stated Viking detection limit. Because of the simplicity of sample handling, TV-GC-MS is still considered the standard method for organic detection on future Mars missions. We suggest that the design of future organic instruments for Mars should include other methods to be able to detect extinct and/or extant life.

Assuntos

RESUMO

Las fracturas orales y maxilofaciales representan un 6 por ciento a 8 por ciento de las fracturas óseas corporales. Estas lesiones son de complejo manejo y exigen un diagnóstico precoz, certero y preciso. El Hospital Regional Hernán Henríquez Aravena, de la ciudad de Temuco, no posee cirujanos orales y maxilofaciales en los equipos de urgencia inmediata, de forma que los ingresos son realizados por otros profesionales. En un año de seguimiento se realizaron 34.931 consultas medico-legales en el Servicio de Urgencia del Hospital Regional Hernán Henríquez Aravena. De esas consultas se escogió una muestra representativa de 742 sujetos de quienes se obtuvo información general y de las lesiones en particular. Se obtuvo también asociación estadística mediante la prueba Chi Cuadrado. Seis por ciento de las consultas en el Hospital Regional Hernán Henríquez Aravena fueron asociadas a fracturas maxilofaciales, donde el grupo con más consultas fueron el de los menores de 20 años. Del total muestral, el 64.4 por ciento correspondió a sujetos del sexo masculino, manteniendo una relación hombre:mujer de 3.1:1; sin embargo, esta relación aumento su diferencia en sujetos mayores de 15 años. El 31.1 por ciento de las consultas fueron causadas por agresiones, mientras que 24.4 por ciento fueron asociadas a las caídas. La principal zona de fractura fue el complejo orbito-naso-etmoidal con un 55.6 por ciento y las fracturas dentoalveolares con un 22.2 por ciento. Existió asociación estadísticamente significativa entre edad, sexo, agresión, fracturas mandibulares y fracturas dentoalveolares (p < 0.05). Los datos reflejan la alta prevalencia de fracturas maxilofaciales en la comuna de Temuco, Chile, siendo similar a lo que ocurre en otras partes del mundo. El grupo de los jóvenes es el de principal consulta donde las agresiones juegan un papel fundamental. Con el presente estudio descriptivo creemos que se justifica plenamente la presencia de cirujanos orales y maxilofaciales en...

The oral and maxillofacial trauma represent a 6% to 8% approximately of the body fractures. These injuries are of complex handling and demand an accurate and precise diagnosis. The Hernán Henríquez Aravena Regional Hospital, of Temuco city, does not have oral and maxillofacial surgeons in the immediate urgency staff, so that first approach to handle those patients is made by other clinicians. After one year, a total of 34,931 consultations were made in the Urgency Service at the Hernán Henríquez Aravena Hospital. Of them, a representative sample of 742 subjects was chosen from which general information and the kind of injuries was obtained. Statistical association with the Chi - Square test was obtained. Six percent of the consultations in the Hernán Henríquez Aravena Regional Hospital were associated to maxillofacial fractures. 64.4% of the sample corresponded to male subjects. The relation man to woman was 3.1:1, displaying a greater difference in patients aged over 15 years. Of the total of sample, the group with more consultations was those aged below 20 years and the 31,1% of the consultations were caused by aggressions, whereas 24,4% were associated to falls. The main zone of fracture was related to the orbit nose etmoidal complex with 55,6% and dental fractures with a 22.2%. Statistically significance association was found between age, sex, aggression, mandible and dental fractures (p < 0,05) The data reflect the high prevalence of maxillofacial fractures in Temuco, Chile, similar to other parts of the world. The group of young people is the one of main consultation where the aggressions play a fundamental roll. With the present descriptive study we think that the presence of oral and maxillofacial surgeons in the urgency staff of the Hernán Henríquez Aravena Regional Hospital, Temuco, Chile is justified totally.

Assuntos

RESUMO

Objetivos: Identificar las alteraciones de crecimiento y desarrollo en los sujetos realizando el trazado del cefalograma y comparar las medidas craneofaciales entre los niños con y sin síndrome de Down en edades comprendidas entre 8 y 11 años en Cali. Materiales y métodos: Estudio de tipo descriptivo, con la participación de 28 niños, 14 con síndrome de Down (SD) estudiantes del Instituto Tobías Emanuel y los 14 sin síndrome de Down que asistían regularmente a la Clínica Integral del Niño y del Adolescente de la Universidad del Valle y que cumplían con unos criterios de inclusión específicos (clasificación Angle I, perfil recto y simetría clínica). Resultados: Como normas clínicas de las medidas utilizadas se emplearon aquellas registradas en los artículos originales de cada autor (9 años); en el grupo 1 (niños con SD) se observó que de las 21 (23.8/100) medidas estudiadas 5 se encontraban aumentadas (perpendicular A a McNamara, convexidad facial, 1/biespinal, arco mandibular y prominencia labial inferior); 5 (23.8/100) medidas por debajo del rango de normalidad (Silla-Nasion, ángulo nasolabial, relación de Witts, altura facial inferior y posterior); 9 (42/100) medidas se encontraron dentro de la regla, aunque acercándose a los límites; 2 medidas,VERT y proporción antero/posterior no otorgaron valores numéricos para categorizarlas. En el grupo 2 (niños sin SD) se observó que sólo 2 (9.5/100) medidas se encontraron aumentadas y que una medida (4.8/100) se encontró disminuída; 16 medidas numéricas estuvieron dentro de los rangos de normalidad. Conclusiones: Al analizar los datos obtenidos existieron variaciones marcadas con respecto a las normas y su desviación clínica aceptada, sobre todo en el grupo de niños con SD, mientras que el grupo sin SD presentó promedios dentro de las normas clínicas corroborando la hipótesis planteada al inicio de la investigación “que existen diferencias en las medidas cefalométricas entre los grupos de niños con SD y los niños sin SD”

Assuntos