383 research outputs found
Synthesis, crystal structure and spectroscopic characterization of a new organic bismuthate (III) [C9H28N4][Bi2Cl10].H2O
The chemical preparation, crystal structure and spectroscopic characterization of [C9H28N4][Bi2Cl10].H2O have been reported. This compound crystallizes in the monoclinic system in space group P21/c and cell parameters a = 12.2385 (6),Ă b = 17.3062 (7), c = 13.0772 (6) ĂâŠ, ĂÂČĂ = 104.475 (5)Ă°, Z = 4 and V = 2681.9 (2) ĂâŠ3. Its crystal structure has been determined and refined to R = 0.049, using 5848 independent reflections. The atomic arrangement can be described by an alternation of organic and inorganic layers. The inorganic layer built up of [Bi2Cl10]4ĂąâŹâ bioctahedra arranged in sandwich between the organic layer. The organic groups are interconnected by the water molecules through N-HĂąâŹÂŠO(W) hydrogen bonds to form infinite zig-zag chains spreading along the b-axis. These Chains are themselves interconnected by means of the NĂąâŹâHĂąâŹÂŠCl hydrogen bonds originating from [Bi2Cl10]4ĂąâŹâ anions, to form a three-dimensional network. Intermolecular ClĂąâŹÂŠCl interactions between adjacent dimeric [Bi2Cl10]4ĂąâŹâ anions have been observed. The compound was also characterized by FT-IR and Raman spectrscopies
Experimental Analysis on the Counter-Current Dumitrescu- Taylor Bubble Flow in a Smooth Vertical Conduct of Small Diameter
In this paper, an experimental investigation on the Dumitrescu-Taylor bubble in counter-current laminar downward
flow in vertical pipe of a small internal diameter pipe is presented. The experimental design is realized to work for
low and stable liquid flow rates. The Dumitrescu-Taylor bubble may be stationary or can be in motion with an
ascending or descending velocity, and this displacement depends on the downward liquid flow rates. Consequently,
the advantage of this device is to carry out the measurements of the velocities inside the gas Dumitrescu-Taylor
bubble by Laser Doppler Velocimetry (LDV). Starting from the visual observations and image acquisitions with a
fast camera, a qualitative description was brought on the hydrodynamic behavior of the liquid film and the ripples
created at the bottom of the Dumitrescu-Taylor bubble. The experimental results show a presence of a long toroĂŻdal
vortex inside the gas bubble. It should be noted that previous work using a hot wire does not show the existence of
this vortex. Additionally, other hydrodynamic magnitudes were measured as the liquid film thickness, the
Dumitrescu-Taylor bubble rising velocity as well as the erosion bubble. Detailed descriptions are brought concerned
this erosion. Strange phenomena have been observed primarily ahead of the nose of bubble and on the side of its end
Reorganization of Coherent Structures Downstream a Circular Cylinder Located between Two Parallel Walls
Experiments were performed at low Reynolds numbers in the range 75 Re 275 in the wake of a circular cylinder
of dc diameter placed symmetrically between two parallel walls of H height. 2D2C particle image velocimetry
(PIV) was used to investigate the flow downstream the cylinder. In the unsteady flow regime downstream the
cylinder, the detached primary vortices (Pi) interact with walls generating secondary ones (Piâ) and modify the
cylinder wake dynamic. The kinematical properties (advection velocity, circulation, rotation kinetic energy, etc.) of
the generated secondary vortices are studied and compared with the primary ones in order to show how the walls
influence the von KĂĄrmĂĄn vortex street. The authors propose here a relation between the circulations and kinetic
energies of primary and secondary vortices
Experimental Study of a Beta Stirling Thermal Machine Type Functioning in Receiver and Engine Modes
In this paper we studied a beta type Stirling machine. At first, we present the adopted theoretical quasi-stationary
model. Then, we pass to the physical and geometrical presentation of this machine. The Latter was experimented
according to two configurations: motor configuration and receiver configuration. For the first configuration, in order
to improve the performances of the machine, we proceeded to the insulation of the machine hot room to reduce losses
by radiation. For the second configuration, the machine is experimented as a heat pump and refrigerator.
Comparisons between the theoretical and experimental results are also presented. We finally validated the results
obtained by the model with experiments
Germination and growth in control and primed seeds of pepper as affected by salt stress
Salinity is an important
abiotic stress which can affect crop
production in the world. One of the simplest
methods for improving salinity tolerance of
plants is seeds priming. This experiment
was conducted to evaluate the effects of
seeds priming with three solutions (KCl ,
NaCl and CaCl2) in germination and later
growth of three pepper (Capsicum annuum
L.) cultivars: Beldi, Baklouti and Anaheim
Chili. Seeds germination was conducted in a
completely randomized design under seven
salinity levels (0, 2, 4, 6, 8, 10 and 12 g L-1)
at room temperature for primed and control
seeds. Plants derived from these germinated
seeds (control and primed) were
transplanted and cultivated in a greenhouse
for 4 months and were irrigated permanently
with seven salinity levels (0, 2, 4, 6, 8, 10
and 12 g L-1). The results showed that
salinity affected all parameters under study
like total germination percentage and
chlorophyll level (a and b). As well, proline
content increased as response to increasing
salinity. The plants derived and grown from
primed seeds showed a considerable
tolerance to salt stress and gave better
results. In fact, priming improved the salt
resistance of pepper owing to more
chlorophyll and proline accumulation.
These results suggest that seed priming
induced possible physiological adjustments
in pepper seeds, especially in the early
stages of development, and could be used as
a suitable tool for improving germination
and growth characteristics under salt stress
conditions
Bis(2,3-dimethylÂanilinium) dihydrogenÂdiphosphate
In the title compound, 2C8H12N+·H2P2O7
2â, the complete dihydrogendiphosphate anion is generated by crystallographic twofold symmetry, with the bridging O atom lying on the rotation axis [PâOâP = 135.50â
(9)°]. In the crystal, the 2,3-xylidinium cations are anchored between ribbons formed by the H2P2O7 entities. Crystal cohesion and stability are supported by electrostatic interÂactions which, together with NâHâŻO and OâHâŻO hydrogen bonds, build up a three-dimensional network
Experimental study of solar energy potential in the gulf of Tunis, Tunisia
Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.This work carries out the availability of the global solar radiation over the site of Borj-Cedria in the gulf of Tunis (36°43â04â N latitude and 10°25â41â E longitude), Tunisia. Global solar radiation variability was assessed on hourly, daily, monthly and seasonal scales. Solar potential in the gulf of Tunis was evaluated using the solar radiation data collected by the meteorological NRG weather station installed in the Centre of Research and Technologies of Energy (CRTEn) in the Borj- Cedria area. The collected measurements during the last three years (2008, 2009 and 2010) were based on 10 minute time step. These data have allowed us to evaluate the global solar flux, the sun duration, the yearly and the seasonal frequency distribution of the global solar radiation. Moreover, a conventional model has been used to estimate the hourly solar radiation on a horizontal plane and it has been validated by experimental measurements in specific days. The results show that the global solar radiation predicted by the conventional model has a good agreement with the experimental data during the clear sky conditions with a relative error percentage of 4.1%. However, the limitation of the conventional model appears under the cloudy sky weather which is proved by the highest value of relative error percentage reaching 14.26% occurred during the autumnal equinox day.dc201
Problématique de la régénération naturelle du Prunus avium au nord-ouest de la Tunisie: Influence des facteurs topographiques et édaphiques
The wild cherry (Prunus avium) is a species very appreciated in cabinet making or as root stock for the cherry tree plantations in the Tunisian northwest. Prunus avium is endangered due to its excessive use by local population. It thus seemed necessary to study the process of the natural regeneration by seed of this species. The obtained results showed that the highest rates of regeneration in small plots were observed at medium altitude (400-600 m), with low slope, exposed northward and in loamy soils. This study allowed us to conclude on the importance of the role played by the environment parameters and other climatic factors such as the minimal and maximal temperature in the natural regeneration of this species in our study zone. To be able to conserve and develop Tunisian wild cherries, we recommend using other techniques of multiplication such as cuttings of root segments.
Key words: Wild cherry, Tunisia, parameters of the medium, multiplication by sowingLe merisier (Prunus avium) est une espĂšce trĂšs prisĂ©e en Ă©bĂ©nisterie ou comme porte greffe pour le cerisier dans le nord-ouest tunisien. Prunus avium est menacĂ© de disparition due Ă son lâutilisation abusive par la population locale. Il est donc apparu nĂ©cessaire dâĂ©tudier le processus de la rĂ©gĂ©nĂ©ration naturelle par semis de cette espĂšce. Les rĂ©sultats obtenus montrent que le taux de rĂ©gĂ©nĂ©ration par semis le plus Ă©levĂ© est observĂ© sur les placettes Ă moyennes altitudes (400-600 m), Ă faible pente, exposĂ© vers le nord-ouest et sur des sols limoneux. Cette Ă©tude nous a permis de conclure lâimportance du rĂŽle jouĂ© par les paramĂštres du milieu et dâautres facteurs climatiques comme la tempĂ©rature minimale et maximale sur la rĂ©gĂ©nĂ©ration naturelle de cette espĂšce au niveau de notre zone dâĂ©tude. Pour pouvoir conserver et mettre en valeur les merisiers tunisiens, nous prĂ©conisons dâutiliser dâautres techniques de multiplication comme le bouturage de segments de racines.
Mots clés: Merisier, Tunisie, paramÚtres du milieu, multiplication par semi
Effects of time-of-day on oxidative stress, cardiovascular parameters, biochemical markers, and hormonal response following level-1 Yo-Yo intermittent recovery test
The aim of this study was to investigate the effect of time-of-day on oxidative stress, cardiovascular parameters, muscle damage parameters, and hormonal responses following the level-1 Yo-Yo intermittent recovery test (YYIRT). A total of 11 healthy subjects performed an intermittent test (YYIRT) at two times-of-day (i.e., 07:00 h and 17:00 h), with a recovery period of â„36 h in-between, in a randomized order. Blood samples were taken at the rest (baseline) and immediately (post-YYIRT) after the YYIRT for measuring oxidative stress, biochemical markers, and hormonal response. Data were statistically analyzed using one-way and two-way repeated measures ANOVA and Bonferroni test at p 2max), maximal aerobic speed, and the total distance covered tended to be higher in the evening (17:00 h). There was also a main effect of time-of-day for cortisol and testosterone concentration, which were higher after the YYIRT in the morning (p  0.05) were similar for the morning and evening test. In conclusion, our findings suggest that aerobic performance presents diurnal variation with great result observed in the evening accompanied by an improvement of hormonal, metabolic, and oxidative responses. These data may help to guide athletes and coaches and contribute to public health recommendations on exercise and muscle damage particularly in the competitive periods
- âŠ