Alpha-decay half-life of Hafnium isotopes reinvestigated by a semi-empirical approach.

- New estimates of partial α-decay half-life, T1/2, for 156-162,174,176Hf isotopes by a semi-empirical, one-parameter model are given. The used model is based on the quantum mechanical tunneling mechanism through a potential barrier, where the Coulomb, centrifugal and overlapping components to the barrier have been considered within the spherical nucleus approximation. This approach enables to reproduce, within a factor 2, the measured T1/2 of ground-state to ground-state (gs-gs) α-transitions for the artificially produced 156-162Hf isotopes. Half-life predictions for α-transitions from the ground-state of 159,161Hf isotopes to the first gamma-excited level of 155,157Yb isotopes are reported for the first time. The model also provides T1/2-values of (2.43±0.28)×1016 a and (1.47±0.19)×1020 a for the naturally occurring 174Hf and 176Hf isotopes, respectively, in quite good agreement with a number of estimates by other authors. In addition, the present methodology indicates that 174,176Hf isotopes exhibit α-transition to the first gamma-excited level of their daughter Ytterbium isotopes which half-lives are found (0.9±0.1)×1018 a and (0.72±0.08)×1022 a, respectively, with a chance of being measured by improved α-detection and α-spectrometry methods available nowadays.

Evaluation of the feeding preference between the aquatic macrophytes Egeria densa and Chara indica by the invasive mollusk Melanoides tuberculata / Avaliação da preferência do molusco invasor Melanoides tuberculata pelas macrófitas aquáticas Egeria densa e Chara indica

Abstract This study evaluated the feeding preference of the invasive mollusk Melaniudes tuberculata between the aquatic macrophytes Egeria densa and Chara indica. The experiment consisted of twelve experimental units (glass aquariums) each of which contained three liters of water and three compartments. Fragments of E. densa and C. indica were placed in separate compartments within each unit; the third compartment, which did not contain macrophytes, was used as the control. Twenty Melanoides tuberculata individuals were placed in each unit and monitored hourly over the course of 24 hours for preferential movements. Physical and chemical water variables were measured at the beginning and end of the experiment. Habitat complexity was determined through collected macrophyte fragments and determined using the Fractop program. After 24 hours, the highest average number of individuals was observed in the treatment with Chara indica (ten individuals), which differed significantly from the treatment with E. densa (four individuals) and the control treatment (two individuals). The number of individuals between the E. densa and control treatment were similar. M. tuberculata showed a clear feeding preference for C. indica.

Resumo O presente trabalho teve como objetivo avaliar a preferência do molusco invasor M. tuberculata pelas macrófitas aquáticas Egeria densa e Chara indica. Doze unidades experimentais (aquários de vidro), com dimensões de 30×15×15 cm, subdivida em três compartimentos foram utilizadas. Em cada unidade experimental foram adicionados três litros de água, sendo que em dois compartimentos foram adicionados aleatoriamente fragmentos de E. densa e C. indica e um compartimento ficou sem planta (controle). Na parte central do aquário foram adicionados os moluscos equidistantes dos três compartimentos. O experimento teve duração de 24 horas, sendo vistoriado e contabilizado o número de organismos presentes em cada compartimento a cada hora. As variáveis ambientais foram medidas no inicio e fim do experimento. Fragmentos de macrófitas foram coletados para determinação da complexidade do habitat através do programa Fractop. Após 24 horas, os resultados mostraram um maior valor médio de indivíduos no tratamento que possuía Chara indica (dez indivíduos), que diferiu significativamente do tratamento com E. densa (quatro indivíduos) e do tratamento controle (dois indivíduos). Os tratamentos com E. densa e o controle foram semelhantes entre si evidenciando, uma possível preferência do molusco por a C. indica.

Evaluation of the feeding preference between the aquatic macrophytes Egeria densa and Chara indica by the invasive mollusk Melanoides tuberculata.

This study evaluated the feeding preference of the invasive mollusk Melaniudes tuberculata between the aquatic macrophytes Egeria densa and Chara indica. The experiment consisted of twelve experimental units (glass aquariums) each of which contained three liters of water and three compartments. Fragments of E. densa and C. indica were placed in separate compartments within each unit; the third compartment, which did not contain macrophytes, was used as the control. Twenty Melanoides tuberculata individuals were placed in each unit and monitored hourly over the course of 24 hours for preferential movements. Physical and chemical water variables were measured at the beginning and end of the experiment. Habitat complexity was determined through collected macrophyte fragments and determined using the Fractop program. After 24 hours, the highest average number of individuals was observed in the treatment with Chara indica (ten individuals), which differed significantly from the treatment with E. densa (four individuals) and the control treatment (two individuals). The number of individuals between the E. densa and control treatment were similar. M. tuberculata showed a clear feeding preference for C. indica.

Distribution and density of the mollusk Donax striatus (Linnaeus, 1767) in a tropical estuarine region in the brazilian semi-arid.

This study evaluated the spatial and temporal distribution and density of the bivalve Donax striatus, at beaches close to the Apodi/Mossoró River estuary, through, six semiannual sampling campaigns were performed between April/2009 and October/2011. The sampled area was delimited by 20 transects that were laid perpendicular to the beach line and extended over 300 m in the intertidal zone. Seven sampling points were established in each transect, organisms and sediment were collected, and water temperature and salinity were recorded. The highest D. striatus average density (103 individuals.m-2) was observed in April/2009 and the lowest (18 individuals.m-2) in October/2010. The highest D. striatus densities occurred in beaches further from the estuarine region as demonstrated by a significant positive correlation (r2 = 0.67 and p = 0.0007). The D. striatus densities presented significant negative correlations with the percentages of organic matter in the water. This species demonstrated an aggregated distribution in the studied area.

Distribution and density of the mollusk Donax striatus (Linnaeus, 1767) in a tropical estuarine region in the brazilian semi-arid / Distribuição e densidade do molusco Donax striatus (Linnaeus, 1767) em região estuarina tropical do semiárido brasileiro

Abstract This study evaluated the spatial and temporal distribution and density of the bivalve Donax striatus, at beaches close to the Apodi/Mossoró River estuary, through, six semiannual sampling campaigns were performed between April/2009 and October/2011. The sampled area was delimited by 20 transects that were laid perpendicular to the beach line and extended over 300 m in the intertidal zone. Seven sampling points were established in each transect, organisms and sediment were collected, and water temperature and salinity were recorded. The highest D. striatus average density (103 individuals.m–2) was observed in April/2009 and the lowest (18 individuals.m–2) in October/2010. The highest D. striatus densities occurred in beaches further from the estuarine region as demonstrated by a significant positive correlation (r2 = 0.67 and p = 0.0007). The D. striatus densities presented significant negative correlations with the percentages of organic matter in the water. This species demonstrated an aggregated distribution in the studied area.

Resumo O objetivo da pesquisa foi verificar a distribuição (espacial e temporal) e a densidade do bivalve Donax striatus em praias próximas ao estuário do Rio Apodi/Mossoró, Rio Grande do Norte (RN), através de seis coletas semestrais (abril/2009 a outubro/2011). Foram dispostos 20 transectos perpendiculares à linha da praia, com 300 m de comprimento na zona intertidal. Em cada transecto foram estabelecidos sete pontos de amostragem e obtidas amostras de organismos e sedimento, foram determinadas a temperatura e salinidade da água. Com os resultados obtidos foi em abril/2009 a maior densidade média de D. striatus (103 indivíduos/m2) e em outubro/2010 a menor densidade (18 indivíduos/m2). As maiores densidades de D. striatus ocorreram em praias afastadas da região estuarina, com correlação significativa e positiva (r2=0,67 e p=0,0007). As densidades de D. striatus apresentaram correlações significativas e negativas com a matéria orgânica. Pôde-se constatar ainda que esta espécie apresentou uma distribuição agregada.