Marine Tar Residues: a Review

Abstract Marine tar residues originate from natural and anthropogenic oil releases into the ocean environment and are formed after liquid petroleum is transformed by weathering, sedimentation, and other processes. Tar balls, tar mats, and tar patties are common examples of marine tar residues and can range in size from millimeters in diameter (tar balls) to several meters in length and width (tar mats). These residues can remain in the ocean envi-ronment indefinitely, decomposing or becoming buried in the sea floor. However, in many cases, they are transported ashore via currents and waves where they pose a concern to coastal recreation activities, the seafood industry and may have negative effects on wildlife. This review summarizes the current state of knowledge on marine tar residue formation, transport, degradation, and distribution. Methods of detection and removal of marine tar residues and their possible ecological effects are discussed, in addition to topics of marine tar research that warrant further investigation. Emphasis is placed on ben-thic tar residues, with a focus on the remnants of the Deepwater Horizon oil spill in particular, which are still affecting the northern Gulf of Mexico shores years after the leaking submarine well was capped

Mercury pollution in doha (Qatar) coastal environment

Surface water and sediment samples were collected from the Doha coastal area and analyzed for content of physico-chemical forms of mercury. Dissolved reactive Hg (2.9 ng L?1) represented 81.0% of the total dissolved Hg (3.5 ng L?1). Organic Hg (0.6 ng L?1) contributed only 5.0% of total Hg. Mercury showed a strong tendency to be associated with suspended matter in Doha coastal waters, as it represented about 73.0% of the total. Total Hg in bulk Doha surface sediments fluctuated between 0.14 and 1.75 ?g g?1 dry weight, with an average of 0.54 � 0.46 ?g g?1 dry weight. The sediment fraction past 63 ?m contained 0.73 ?0.60?g g?1 dry weight total Hg. Leachable and methyl Hg averaged 0.10 � 0.11 and 0.02 �0.03 ?g g?1 dry weight, respectively, in the <63-?m sediment fraction. There is a general trend for all Hg species determined in water and sediments to decrease seaward. The significantly elevated Hg levels at certain locations indicated that the main Hg sources to Doha coastal environment are leachate from the solid waste disposal site, the two harbors, and surface-water discharge.Scientific and Applied Research CenterWiley Online Librar

Reduction kinetics of ceria surface by hydrogen

Powdered cerium dioxide (ceria, CeO2) as compressed, sintered pellets, of porosity 16.4% and density 5.99 g cm?3, were treated in hydrogen flow at 1 atm and various temperatures to effect reduction. The electrical conductivity was measured in situ during the reduction process. The conductivity increased continuously during the hydrogen treatment because of the creation of anion vacancies and accompanying small polaron electrons. The conductivity�time relationship exhibits three distinct regions indicated as I, II, and III. For each of steps I and II, the conductivity increases exponentially with the reduction. It is suggested from the kinetic analysis of the data that region I is due to desorption of adsorbed oxygen states. Region II appears to be the reduction of surface lattice oxygen. The kinetics of the reactions in both regions I and II obey first-order rate laws with similar activation energies of 86 and 115 kJ mol?1, respectively. Thermogravimetric experiments were used to determine the time needed to remove one monolayer of adsorbed oxygen from the surface. This could be used to estimate the activation energy of the desorption process at 95 kJ mol?1�close to the value measured by conductivity measurements. After completing the surface reduction the electrical conductivity subsequently increased slowly during region III. This step is assigned to a diffusion-controlled process during which the bulk of the pellets are reduced. 1H MASNMR and in situ PXRD experiments confirmed the chemical nature of each of the three steps

متراكبات الروثنيوم الثنائي والثلاثي والأوزميوم الثلاثي مع المرتبطات المعطية المتعادلة للنتروجين - نتروجين وخواصها في الاكسدة الحفزية

A number of new complexes [RunCl2 (PPh3)2L], [RumX3 (AsPh3)L] and [OsnICl3(PPh3)L'] [L= o-anthranilonitrile(anth), o-phenylenediamine(phdm), l,10-phenanthroline(phen), 2,2'-bipyridine(bipy); L' = Phen, bipy; X = Cl, Br] have been prepared. They were characterized by spectroscopic techniques and investigated by cyclic voltammetry. The ruthenium(III) complexes were found to be more efficient catalytic oxidants than those of ruthenium(II), while osmium(III) complexes showed a weak catalytic activity. In the presence of N-methylmorpholine-N-oxide as a co-6xidant, the ruthenium catalysts oxidised primary alcohols to aldehydes and secondary alcohols to ketones.تم تحضير عدد من المتراكبات الجديدة للروثنيوم الثنائي والثلاثي وكذلك الأوزميوم الثلاثي مع مرتبطات ثنائية المخلب متعادلة الشحنة من نوع النتروجين - نتروجين . وقد تم التعرف على تلك المتراكبات بالطرق الطيفية المختلفة ودرست بجهاز الفولتامتر الدائري . ووجد أن متراكبات الروثنيوم الثلاثي أكثر كفاءة كعوامل مؤكسدة حفازة للكحولات الأولية والثانوية التي تتأكسد إلى الدهيدات وكيتونات

Assessment of the quality of root canal fillings performed on extracted teeth by undergraduate dental students in a sample from Saudi Arabia

Abstract Background The educational process in the field of endodontics commences with preclinical exercises to enhance students’ proficiency in cleaning, shaping, and performing root canal fillings. Therefore, this study aimed to radiographically evaluate the technical quality of root canal fillings performed by preclinical students on extracted teeth at the College of Dentistry, University of Ha’il, Saudi Arabia. Methods A total of 788 extracted human teeth received root canal treatment by undergraduate students. The samples were then gathered and radiographically assessed using the three quality criteria of length, density, and taper. The category of root canal fillings was classified as either acceptable or unacceptable. The criteria for evaluating the acceptability of filling quality were defined based on the presence of adequate length, density, and taper. The effectiveness of root canal fillings was also evaluated in relation to the tooth type, sex, and treatment year. The agreement between the examiners was evaluated using Cohen’s kappa test, and the relationship between the research variables was determined using the chi-squared test. The significance threshold was set at 0. 05. Results The overall quality of root filling was determined to be satisfactory in 532 (67.5%) of 788 endodontically treated extracted teeth. The majority of the research sample (88.1%) had enough length, 89.6% had adequate density, and 86.4% had acceptable taper. The quality of anterior teeth was substantially better than that of posterior teeth (p < 0.001). Our findings showed that the quality of root canals was better in 2022 than it had been in earlier years (p = 0.001). The three RCT quality criteria differed significantly when compared between sexes (p = 0.002). Conclusions The quality of the root canal fillings completed by undergraduate students was rated as acceptable. The findings of the research suggest that the implementation of routine assessments to evaluate the technical competence of undergraduate dental students performing root canal treatments could provide significant insights into the efficacy of the curriculum requirements