Switching from Electron to Hole Transport in Solution-Processed Organic Blend Field-Effect Transistors

Organic electronics became an attractive alternative for practical applications in complementary logic circuits due to the unique features of organic semiconductors such as solution processability and ease of large-area manufacturing. Bulk heterojunctions (BHJ), consisting of a blend of two organic semiconductors of different electronic affinities, allow fabrication of a broad range of devices such as light-emitting transistors, light-emitting diodes, photovoltaics, photodetectors, ambipolar transistors and sensors. In this work, the charge carrier transport of BHJ films in field-effect transistors is switched from electron to hole domination upon processing and post-treatment. Low molecular weight n-type N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) was blended with p-type poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) and deposited by spin-coating to form BHJ films. Systematic investigation of the role of rotation speed, solution temperature, and thermal annealing on thin film morphology was performed using atomic force microscopy, scanning electron microscopy, and grazing incidence wide-angle X-ray scattering. It has been determined that upon thermal annealing the BHJ morphology is modified from small interconnected PDI8-CN2 crystals uniformly distributed in the polymer fraction to large planar PDI8-CN2 crystal domains on top of the blend film, leading to the switch from electron to hole transport in field-effect transistors

NIVELES DE DDT EN TEJ IDO ADIPOSO MATERNO, SUERO SANGUÍNEO Y LECHE DE MADRES RESIDENTES EN VERACRUZ, MÉXICO. ESTUDIO 1997-1999

The levels of DDT and metabolites were determined in maternal adipose tissue, maternal blood serum and mature milk of 112 volunteers in order to observe the gradient of concentrations. The results obtained indicated the highest concentration of metabolite pp’DDE in adipose tissue at 3.76 mg/kg, followed by 3.49 mg/kg in blood serum and 3.23 mg/kg in mature milk. The same tendency was revealed for the insecticide pp’DDT with 0.97 mg/kg in adipose tissue, 0.82 mg/kg in blood serum and 0.51 mg/kg in mature milk. The higher concentrations of total DDT in mature milk correspond to the suburban population at 4.84 mg/kg compared to 2.49 mg/kg for the Veracruz population. Moreover, the elevation of their levels according to age was observed ranging from 2.97 mg/kg in mothers under 20 years of age, up to 4.60 mg/kg in mothers over 40. There was also a decreased tendency with parity from 4.10 mg/kg in primiparous to 3.41 mg/kg in triparous. The DDT accumulated in maternal adipose tissue forms an equilibrium with blood serum and then is excreted with the endogenous fat of maternal milk.Se determinaron los niveles del DDT y sus metabolitos en tejido adiposo materno, suero materno y leche materna madura de 112 voluntarias para observar el posible gradiente de concentración. Los resultados indicaron mayor concentración del metabolito pp’DDE en tejido adiposo con 3.76 mg/kg, seguido por 3.49 mg/kg en suero sanguíneo y 3.23 mg/kg en leche materna madura. La misma tendencia reveló el insecticida pp’DDT con 0.97 mg/kg en tejido adiposo, 0.82 mg/kg en suero sanguíneo y 0.51 mg/kg en leche madura. La mayor concentración del DDT total en leche madura se determinó en la población suburbana de 4.84 mg/kg en comparación con 2.49 mg/kg en la de Veracruz, así como un ascenso con la edad de 2.97 mg/kg en madres menores de 20 años a 4.60 mg/kg en madres mayores de 40 años y un descenso con la paridad con 4.10 mg/kg en primíparas y 3.41 mg/kg en tríparas. El DDT acumulado en el tejido adiposo materno forma un equilibrio con el suero sanguíneo y se excreta con las grasas endógenas que participan en la formación de la leche.

NIVELES DE PLAGUICIDAS ORGANOCLORADOS EN CARNE Y GRASA DE BOVINO PROCEDENTES DE VERACRUZ, MÉXICO

The levels of organochlorine pesticides in 218 samples of fat and 165 samples of organs and meat Collected from bovines slaughtered in the municipal slaughterhouse of Veracruz were determined during 1994. Analysis were carried out by gas chromatography with electron capture detector. From the analyzedresidues, pp'DDT presented the highest mean levels in organs and meat, reaching the maximum meanlevel of 2.713 mg/kg in lung samples, that was statistically difierent (p<0.05) composed with mean levels of other organs. The mean levels of HCB in fat samples from abdominal cavities and the mean levels oftotal DDT in fat samples from abdominal cavities were statistically different (p<<O.O5). Apparently, the overall coiitamination with organochlorine pesticides was found to be higher than in other countries. Nevertheless, these concentrations were bellow the United States tolerarice limits, except for the β-HCH.Durante 1994 se colectaron un total de 218 muestras de tejido adiposo de diversas regiones anatómicas y 165 muestras de distintas vísceras y músculos de bovinos sacrificados en el rastro municipal de la ciudad de Veracruz que se analizaron por cromatografía de gases con detector de captura de electrones para determinar la presencia y distribución de la contaminación por plaguicidas organoclorados. El pp'DDT presentó los niveles promedio más altos encontrados en vísceras y músculos, como es el caso en vísceras de pulmón de 2.713 mg/kg, estadísticamente diferente (p<0.05) a los valores medios detectados en otras vísceras. Se hallaron diferencias estadísticamente significativas (p<0.05) en los niveles medios del HCB de las grasas de la cavidad abdominal, así como entre los niveles del DDT total de la grasa abdominal. Los niveles de los plaguicidas organoclorados manifestados en las muestras revelaron la existencia de una contaminación mayor a la reportada en otros países. Sin embargo, estos valores se encontraron por debajo de las tolerancias establecidas en los Estados Unidos de América con excepción del β-HCH

Self-Aligned Bilayers for Flexible Free-Standing Organic Field-Effect Transistors

[Image: see text] Free-standing and flexible field-effect transistors based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene)/polystyrene bilayers are obtained by well-controlled phase separation of both components. The phase separation is induced by solvent vapor annealing of initially amorphous blend films, leading to crystallization of TIPS-pentacene as the top layer. The crystallinity and blend morphology strongly depend on the molecular weight of polystyrene, and under optimized conditions, distinct phase separation with a well-defined and trap-free interface between both fractions is achieved. Due to the distinct bilayer morphology, the resulting flexible field-effect transistors reveal similar charge carrier mobilities as rigid devices and additionally pronounced environmental and bias stress stabilities. The performance of the flexible transistors remains stable up to a strain of 1.8%, while above this deformation, a close relation between current and strain is observed that is required for applications in strain sensors

Role of oxygen within end group substituents on film morphology and charge carrier transport in thiophene/phenylene small-molecule semiconductors

In this study, the end group polarity of (5,5′)-biphenyl-(2,2’)-bithiophenes (PTTPs) was systematically varied from alkyl (1) to alkoxy (2) with one oxygen atom to glycol (3) with two oxygen atoms while the overall length of the end groups is kept constant. Thin films of the three compounds were sublimated at different substrate temperatures and their morphology, crystallinity and charge carrier transport in field-effect transistors was investigated to draw structure-property relationships for the PTTP derivatives. For all three compounds, the effective charge carrier mobility is improved with higher substrate temperatures at which films with higher crystallinity and larger grains are formed. The effective mobility decreases with higher polarity of the end groups from alkyl to alkoxy and glycol. The reliability factor of the alkyl (1) and alkoxy (2) substituted PTTPs decreases with higher substrate temperature, but at the same time this value is enhanced for the glycol substituted molecules (3). The transistors of 3 prepared at higher substrate temperatures also show a reduced threshold voltage and smaller hysteresis in the transfer characteristics. These insights are important for the understanding of the impact of oxygen incorporation into side chain/end group substituents of organic semiconductors and their implementation in organic electrochemical transistors, thermoelectrics and photovoltaics

EVALUACIÓN DE LOS NIVELES DE DDT Y HCH EN EL TEJIDO ADIPOSO DE ALGUNAS PERSONAS FALLECIDAS EN EL ESTADO DE VERACRUZ, MÉXICO

During the 1998, 1991 and 1992 period a total of 177 samples of human adipose tissue were takenfrom abdominal cavities and the following organochlorine pesticides were determined: P-HCH, pHCH,pp'-DDE, op'-DDT and pp'-DDT. The determined residue levels of y-HCH were higlier, while the levelsof P-HCH were comparable with those describe. in other countries. The total DDT amount tended toincrease, reaching 24.82 mglkg (on fat basis) in 1992, which was mainly composed by the metabolite DDE18.19 mgíkg (on fat basis). The contamination was probably due to intake of foods of animal ongin suchas milk and meat products, extremely contaminated by DDE and this substance was then accumulated iiithe adipose tissue.Se determinaron los residuos de los plaguicidas organoclorados P-HCH, y-HCH, pp'-DDE, op'-DDT ypp'-DDT en 177 muestras de tejido adiposo, tomadas de la región abdominal de personas fallecidas en la Ciudad de Veracruz del estado de Veracruz, México, durante los años 1988, 199 1 y 1992. Los niveles de y-HCH fueron superiores a los descritos en otros países, mientras que los correspondientes a P-HCH fueron comparables a ellos. El contenido total de DDT presentó una tendencia ascendente alcanzando un nivel de 24.82 mgíkg (en base lipídica) en 1992, constituido principalmente por el metabolito DDE con una concentración de 18.91 mgkg (en base lipídica). Esta contaminación pudo deberse principalmente a los alimentos de origen animal, como son los productos lácteos y cárnicos, altamente contaminados por DDE. que al ser ingerido se acumuló en el tejido adiposo

Self-organization of developing embryo using scale-invariant approach

<p>Abstract</p> <p>Background</p> <p>Self-organization is a fundamental feature of living organisms at all hierarchical levels from molecule to organ. It has also been documented in developing embryos.</p> <p>Methods</p> <p>In this study, a scale-invariant power law (SIPL) method has been used to study self-organization in developing embryos. The SIPL coefficient was calculated using a centro-axial skew symmetrical matrix (CSSM) generated by entering the components of the Cartesian coordinates; for each component, one CSSM was generated. A basic square matrix (BSM) was constructed and the determinant was calculated in order to estimate the SIPL coefficient. This was applied to developing <it>C. elegans </it>during early stages of embryogenesis. The power law property of the method was evaluated using the straight line and Koch curve and the results were consistent with fractal dimensions (fd). Diffusion-limited aggregation (DLA) was used to validate the SIPL method.</p> <p>Results and conclusion</p> <p>The fractal dimensions of both the straight line and Koch curve showed consistency with the SIPL coefficients, which indicated the power law behavior of the SIPL method. The results showed that the ABp sublineage had a higher SIPL coefficient than EMS, indicating that ABp is more organized than EMS. The fd determined using DLA was higher in ABp than in EMS and its value was consistent with type 1 cluster formation, while that in EMS was consistent with type 2.</p

Stable population structure in Europe since the Iron Age, despite high mobility

Ancient DNA research in the past decade has revealed that European population structure changed dramatically in the prehistoric period (14,000-3000 years before present, YBP), reflecting the widespread introduction of Neolithic farmer and Bronze Age Steppe ancestries. However, little is known about how population structure changed from the historical period onward (3000 YBP - present). To address this, we collected whole genomes from 204 individuals from Europe and the Mediterranean, many of which are the first historical period genomes from their region (e.g. Armenia and France). We found that most regions show remarkable inter-individual heterogeneity. At least 7% of historical individuals carry ancestry uncommon in the region where they were sampled, some indicating cross-Mediterranean contacts. Despite this high level of mobility, overall population structure across western Eurasia is relatively stable through the historical period up to the present, mirroring geography. We show that, under standard population genetics models with local panmixia, the observed level of dispersal would lead to a collapse of population structure. Persistent population structure thus suggests a lower effective migration rate than indicated by the observed dispersal. We hypothesize that this phenomenon can be explained by extensive transient dispersal arising from drastically improved transportation networks and the Roman Empire's mobilization of people for trade, labor, and military. This work highlights the utility of ancient DNA in elucidating finer scale human population dynamics in recent history

Raspodjela lindana u vodi, sedimentu i ribama iz rijeke Warri (Delta Nigera, Nigerija)

This paper is the first attempt to quantify the levels and the distribution pattern of lindane in the surface water, sediment and fish (Chrysichthys furcatus and Tilapia zilli). The samples were collected from three stations (Ovwian, Ekakpamre, and Ovu) of the Warri River in the western Niger Delta of Nigeria in 2006: during the dry (January-April) and wet seasons (May-August). The analysis included a total of 96 samples made up of 24 samples each for water, sediment, and fish. The pesticide levels were analysed using high performance liquid chromatography to elucidate its distribution in various environmental compartments. Residue levels in the matrices ranged from below the detection limit (BDL) to 1.37µg L-1 in water, BDL to 12.66 µg g-1 dry weight (dw) in sediment, BDL to 16.67 µg g-1dw in Chrysichthys furcatus, and BDL to 0.15 µg g-1dw in Tilapia zilli .The observed values were above the ecological benchmarks (0.01 µg L-1) recommended by the Nigerian Environmental Protection Agency and European Union. They were also relatively higher than in previous studies on the Nigerian environment, which calls for regular monitoring of the Niger Delta water bodies.Istražene su pojava i raspodjela lindana u površinskoj vodi, sedimentu i dvije vrste riba Chrysichthys furcatus i Tilapia zilli iz rijeke Warri u zapadnom dijelu delte Nigera (Nigerija). Uzorci su skupljeni 2006. godine na tri postaje (Ovwian, Ekakpamre i Ovu) tijekom sušne (siječanj - travanj) i vlažne sezone (svibanj - kolovoz). Analizirano je ukupno 96 uzoraka: po 24 uzorka vode, sedimenta i riba. Razine pesticida odre|ene su primjenom tekućinske kromatografije visoke djelotvornosti (HPLC) te je utvr|ivana njihova raspodjela u različitim dijelovima okoliša. Koncentracije rezidua u uzorcima vode bile su u rasponu: ispod granice detekcije (BDL) do 1,37 µg L-1, u sedimentu: BDL do 12,66 µg g-1 suhe tvari, u ribama Chrysichthys furcatus: BDL do 16,67 µg g-1 suhe tvari te Tilapia zilli: BDL do 0,15 µg g-1 suhe tvari. Određene vrijednosti bile su ispod graničnih vrijednosti (0,01 µg L-1) propisanih od Nigerijske uprave za zaštitu okoliša i Europske unije. Kako su dobivene vrijednosti bile relativno više u odnosu na podatke iz ranijih istraživanja okoliša u Nigeriji, istaknuta je potreba trajnog monitoringa vodotoka u delti Nigera