Ecology of Shakla heel (Brahmanbaria), Bangladesh

The bed Shakla, comprising an average area of 75.0 ha is located in the northeastern region (Brahmanbaria district) of Bangladesh. The study was carried out to assess the ecological aspects of bed ecosystem. Surface run-off and increase inflow of rain water from the upper stretch during monsoon cause inundation and resumption of connection between beel and parent rivers. The range of dissolved oxygen (DO) content ( 4.5-8.9 mg/L) was found congenial for aquatic life. pH was in the alkaline range (7.3-8.5) and free C02 was reletavely high. Lower values of total hardness and total alkalinity indicated less nutrients in the beel water. A wide variation (1.4-27.2 x 103 ceHs/L) in the standing crop of total plankton was recorded during study period of which phytoplankton alone contributed about 90%. Phytoplankton diversity in the beel represented by three groups viz. Chlorophyceae, Myxophyceae and Bacillariophyceae in order of abundance. A total of 52 fish species belonging to 36 genera, 20 families and 1 species of prawn were identified so far from the beel. About l3 types of fishing method were found in operation. Seine nets (moshari berja, ghono berjal) and gill net (current jal) were identified as detrimental gear killing juveniles of different species during post spawning period. Kua fishing was also found harmful due to dewatering nature. A total of 11 species belonging to 11 genera and 10 families of aquatic weeds were identified from the beet The eggs of Macrobrachium Jamarrei were identified into the Najas najas vegetation during April-September.

Electric conduction improvement of well-structured multi-walled carbon nanotubes

We characterized the electrical conductance of well-structured multi-walled carbon nanotubes (MWCNTs) which had post-treated by a rapid vacuum arc thermal annealing process and structure defects in these nanotubes are removed. We found that the after rapid vacuum arc annealing, the conductivity of well-structured MWCNTs can be improved by an order of magnitude. We also investigated the conductivity of MWCNTs bundle by the variation of temperatures. These results show that the conductance of annealed defect-free MWCNTs is sensitive to temperature imply the phonon scatting dominated the electron conductions. Compare to the well-structured MWCNTs, the defect scattering dominated the electron conduction in the as-grown control sample which has large amount of structure defects. A detail measurement of electron conduction from an individual well-structured MWCNT shows that the conductivity increases with temperatures which imply such MWCNTs exhibited semiconductor properties. We also produced back-gated field-effect transistors using these MWCNTs. It shows that the well-structured MWCNT can act as p-type semiconductor. © 2010 IEEE.

Studies on the chemical control of psychrophilic bacterial spoilage of fish. 2 - The effect of antibiotics on the growth of psycrophilic bacteria isolated from marine fish

Among the various antibiotics tried, tetracyclines particularly chlorotetracycline (CTC), chloramphenicol and chlorostrep were found to be fairly effective at 8 and 10 p.p.m. levels. The order of sensitivity to CTC among the six genera studied was found to be Achromobacterof antibiotics for commercial application are discussed.

Behaviour of marine microflora towards antibiotics 1. Sensitivity towards chlortetracycline (CTC)

The sensitivity of 61 cultures of bacteria isolated from fish towards chlortetracycline (CTC) at 5 ppm and 20 ppm levels has been determined on two solid media: sea water agar (SWA) and a distilled water based medium consisting of peptone, beef extract, glucose and NaCI (PBGA). The cultures employed consisted of (i) gram-negative rods of marine origin (Achromobacter, Pseudomonas, Vibrio and Flavobacterium) and (ii) gram positive organisms (Micrococci and Corynebacterium). Depending on the inhibition zone diameter, the order of CTC sensitivity was found to be Pseudomonasof 5 and 20 ppm. The SWA enhanced the development of resistance in majority of the cultures as compared to PBGA. PBG broth containing CTC at less than 10 ppm exerted a bacteriostatic effect only while that containing 10 ppm or more exerted a bactericidal effect on Achromobacter, Pseudomonas and Micrococci cultures. The significance of these results in fish preservation by CTC is discussed.

Heavy metal concentrations in some organs of African catfish (Clarias gariepinus) from Eko-Ende Dam, Ikirun, Nigeria

The contents of the heavy metals Fe, Zn, Cu, Mn, Pb, Cd and As were examined in the liver, heart, gills, kidney and muscles of the fish Clarias gariepinus from Eko-Ende dam in Ikirun, the capital of Ifelodun Local Government of Osun State, Nigeria. C. gariepinus is the fish of choice and the most demanded in the southwest of Nigeria. The highest metal concentrations were in the liver and the gills while the lowest was in the muscles. The general deceasing order of metal accumulation in the organs was Fe > Zn > Cu > Mn > Cd. Lead and arsenic were not detected in any organ. The values were of lower concentrations than found in many other dams and rivers in Nigeria and some other countries. The values were also lower than the FAO/WHO recommended maximum limits in fish samples, making the fish to be safe and not of any hazards for the consumers.

Spoilage of spotted seer (Scomberomorous guttatus) during ice storage

Quality deterioration of seer held directly in contact with ice, in different forms, fillets and chunks, and of chunks held in ice but without direct contact, was studied for a period of 15 days. While the chunks held out of contact with ice were acceptable up to 13 days based on organoleptic evaluations, the chunks and fillets held in direct contact with ice were acceptable only up to 10 days. The order of preference of the samples at any interval of ice storage was chunks held out of contact with ice>chunks held directly in ice>fillets held directly in ice. The changes in the chemical quality of these samples were also in the same order, the deterioration being maximum in fillets and least in chunks kept out of contact with ice.

Note on an abnormal catch of Catla catla in Hirakud reservoir

During the 1973 experimental fishing operations in the Hirakud Reservoir, it was found that though 11 species of fish occur in the reservoir only four species (Silondia silondia, Labeo fimbriatus, Cirrhina mrigala and Catla catla) predominate the catch in the order of abundance. This paper gives details of fishing operations and gears utilised.

Proximate composition of 17 species of Indian fish

Miscellaneous fish from the catches of shrimp trawlers constitute a major portion of the marine fish catch in India, its quantity in annual landing being of the order of 50,000 tons. At present it is often not brought to the shore since it fetches only very low price. It consists of several species and is a cheap source of animal protein. Attempts are made in India in various centres (Anon. 1972-73) to utilise them effectively by formulating various speciality products acceptable to consumers.

Preservation of Sardinella longiceps in iced and chilled seawater. Part 1 - Changes during storage with particular reference to bacterial load and nitrogenous compounds

Oil sardines in prime condition were subjected to onboard chilling. Two lots were chilled in CSW (samples C and CI), a third lot was chilled in crushed ice (sample I) and a fourth lot left not iced on deck (Sample AI). Upon landing sample AI was iced and sample CI was removed from the CSW and iced. All the four samples were kept in a chilled room for storage studies. The fish chilled and stored in CSW recorded the least, and the fish subjected to delayed icing, the highest values for all the indices of spoilage namely, free amino nitrogen, trimethylamine (TMA) and total volatile base nitrogen (TVBN). The total psychrophilic bacterial number also showed a similar trend. The organoleptic assessment of the cooked samples revealed C I, CI, AI to be the order of preference throughout the storage. This assessment was found to hold good for the rest of the parameters as well. The CSW held fishes were found to be distinctly superior to the iced ones for the first five days of storage. Such a marked prevalence in quality for five days would suffice for the fish to fetch a premium in the market over other landings of the same fish whether chilled or not chilled. Chilling on board in CSW and icing the same after landings, did not show encouraging results.

Relation between weight and linear measurement of shell in C. madrasensis (Preston)

Relation of weight to height, length and breadth in the Indian backwater oyster Crassostrea madrasensis (Preston) is reported. The relative importance of the variables on weight was found to be height, length and breadth in their order of preference. The multiple regression V = -0.4017 + 0.46743 X + 0.8278 Y + 0.1130 Z can be used to estimate the meat weight (logarithm) for given dimensions of length, height and breadth (all in logarithms). An exponential relation between weight and height is also observed.

Stabilizing effect of surrounding gas flow on a plane liquid sheet

The stability of a plane liquid sheet is studied experimentally and theoretically, with an emphasis on the effect of the surrounding gas. Co-blowing with a gas velocity of the same order of magnitude as the liquid velocity is studied, in order to quantify its effect on the stability of the sheet. Experimental results are obtained for a water sheet in air at Reynolds number Rel = 3000 and Weber number W e = 300, based on the half-thickness of the sheet at the inlet, water mean velocity at the inlet, the surface tension between water and air and water density and viscosity. The sheet is excited with different frequencies at the inlet and the growth of the waves in the streamwise direction is measured. The growth rate curves of the disturbances for all air flow velocities under study are found to be within 20 % of the values obtained from a local spatial stability analysis, where water and air viscosities are taken into account, while previous results from literature assuming inviscid air overpredict the most unstable wavelength with a factor 3 and the growth rate with a factor 2. The effect of the air flow on the stability of the sheet is scrutinized numerically and it is concluded that the predicted disturbance growth scales with (i) the absolute velocity difference between water and air (inviscid effect) and (ii) the square root of the shear from air on the water surface (viscous effect).

Stabilizing effect of surrounding gas flow on a plane liquid sheet

The stability of a plane liquid sheet is studied experimentally and theoretically, with an emphasis on the effect of the surrounding gas. Co-blowing with a gas velocity of the same order of magnitude as the liquid velocity is studied, in order to quantify its effect on the stability of the sheet. Experimental results are obtained for a water sheet in air at Reynolds number Rel = 3000 and Weber number We = 300, based on the half-thickness of the sheet at the inlet, water mean velocity at the inlet, the surface tension between water and air and water density and viscosity. The sheet is excited with different frequencies at the inlet and the growth of the waves in the streamwise direction is measured. The growth rate curves of the disturbances for all air flow velocities under study are found to be within 20% of the values obtained from a local spatial stability analysis, where water and air viscosities are taken into account, while previous results from literature assuming inviscid air overpredict the most unstable wavelength with a factor 3 and the growth rate with a factor 2. The effect of the air flow on the stability of the sheet is scrutinized numerically and it is concluded that the predicted disturbance growth scales with (i) the absolute velocity difference between water and air (inviscid effect) and (ii) the square root of the shear from air on the water surface (viscous effect).

Comparison of sensory characteristics and biochemical parameters in commercial frozen prawns

Commercial samples of frozen shrimp of different styles of presentation and size grades were tested for sensory, physical (cooked yield and pH) and biochemical characteristics (moisture, total nitrogen, water extractable nitrogen, nonprotein nitrogen, alpha amino nitrogen, total volatile nitrogen and trimethylamine nitrogen). The test results are compared and correlated. The order of preference of the samples were HL>PUD>P & D. There was significant correlation between sensory score of cooked sample and WEN, NPN and ∞ – NHsub(2)-N values. TVN and TMA-N did not exhibit any correlation with sensory score. It is inferred that in quality measurement of frozen shrimps of commerce the quantity of water soluble components and the total dry matter can be used to support the sensory test results.

On the stabilisation of turbulent lifted flames

This study explores the stabilisation mechanisms of turbulent lifted flames by examining the scalar dissipation rate (SDR) of both passive and reactive scalars and their cross dissipation (CDR) in the stabilisation region. DNS results of a laboratory scale hydrogen turbulent lifted flame has been used for this analysis. Various definitions of the flame leading edge (FLE) has been compared and differences are illustrated. Time and spatial averaged statistic of SDR and CDR were examined. It was found that the averaged SDR for the mixture fraction at FLE was well below the reference quenching value for stoichiometric mixture. The averaged SDR for the progress variable is in the same order of the unstrained premixed laminar flame value. It was observed that the averaged CDR changed from negative to weakly positive at FLE. The change in sign was explained by a change in the relative alignment of the gradients of mixture fraction and progress variable. It was thus evident that the CDR was a good marker for stabilisation region and an important quantity in stabilisation mechanism.

Size distribution of heavy mineral grains in some modern Nile Delta coastal sands, Egypt

This study includes determination and discussion of the texture and heavy mineral compositions of some modem Nile Delta coastal sands (river, coastal dune, beach-face, and nearshore marine) in order to delineate the process and factors that regulate the size distribution of heavy mineral grains comprising these coastal sands. Textural analysis of unseparated bulk samples indicate that the examined four types of sands differ in their mean grain sizes and degree of sorting. However, analysis of size distribution curves of 10 heavy mineral species or group of species in the four environments having the same general shape and nearly similar in that general order of arrangement. However, these curves vary both in median sizes and sorting. The size distribution of a heavy mineral in the Nile Delta coastal sands appear to depend on: (1) range of grain size fractions in each sample, (2) relative availability of heavy mineral in each size grade of the sample, (3) specific gravity of minerals comprising these sands, and (4) some other unknown factor or factors. Results of size measurement of heavy minerals indicated that increasing specific gravity is accompanied by increasing fineness of the heavy minerals. This study may be useful in search for marine placers and understanding the processes of grain-sorting on the sea beaches.