Abstract: The Hall Coefficient (HC) and the Magnetoresistance (MR) have been studied in two-dimensional systems. The HC and the MR in Rectangular Quantum Wire (RQW) subjected to a crossed DC electric field and magnetic field in the presence of a Strong Electromagnetic Wave (EMW) characterized by electric field are studied in this work. Using the quantum kinetic equation for electrons interacting with optical phonons, we obtain the analytic expressions for the HC and the MR with a dependence on magnetic field, EMW frequency, temperatures of systems and the length characteristic parameters of RQW. These expressions are different from those obtained for bulk semiconductors and cylindrical quantum wires. The analytical results are applied to GaAs/GaAs/Al. For this material, MR depends on the ratio of the EMW frequency to the cyclotron frequency. Indeed, MR reaches a minimum at the ratio 5/4, and when this ratio increases, it tends towards a saturation value. The HC can take negative or positive values. Each curve has one maximum and one minimum. When magnetic field increases, the HC is negative, achieves a minimum value and then increases suddenly to a maximum with a positive value. This phenomenon differs from the one observed in cylindrical quantum wire, which does not have maximum and minimum values.
Abstract: Torrefaction of biomass pellets is considered as a
useful pretreatment technology in order to convert them into a high
quality solid biofuel that is more suitable for pyrolysis, gasification,
combustion, and co-firing applications. In the course of torrefaction,
the temperature varies across the pellet, and therefore chemical
reactions proceed unevenly within the pellet. However, the
uniformity of the thermal distribution along the pellet is generally
assumed. The torrefaction process of a single cylindrical pellet is
modeled here, accounting for heat transfer coupled with chemical
kinetics. The drying sub-model was also introduced. The nonstationary
process of wood pellet decomposition is described by the
system of non-linear partial differential equations over the
temperature and mass. The model captures well the main features of
the experimental data.
Abstract: In the present study, a numerical approach to describe the pyrolysis of a single solid particle of wood is used to study the influence of various conditions such as particle size, heat transfer coefficient, reactor temperature and heating rate. The influence of these parameters in the change of the duration of the pyrolysis cycle was studied. Mathematical modeling was employed to simulate the heat, mass transfer, and kinetic processes inside the reactor. The evolutions of the mass loss as well as the evolution of temperature inside the thick piece are investigated numerically. The elaborated model was also employed to study the effect of the reactor temperature and the rate of heating on the change of the temperature and the local loss of the mass inside the piece of wood. The obtained results are in good agreement with the experimental data available in the literature.
Abstract: Electro-osmosis in clayey soils and sediments, for
purposes of clay consolidation, dewatering, or cleanup, and electro
injection in porous media is widespread recent decades. It is
experimentally found that the chemical properties of porous media
especially PH change the characteristics of media. Electro-osmotic
conductivity is a function of soil and grout material chemistry,
altering with time. Many numerical approaches exist to simulate the
of electro kinetic flow rate considering chemical changes. This paper
presents a simplified analytical solution for constant flow rate based
on varying electro osmotic conductivity and time dependent viscosity
for injection of colloidal silica.
Abstract: In this study, we investigated the thixotropic behavior
of two clays used in fabrication of ceramic. The structural kinetic
model (SKM) was used to characterize the thixotropic behavior of
two different kinds of clays used in fabrication of ceramic. The SKM
postulates that the change in the rheological behavior is associated
with shear-induced breakdown of the internal structure of the clays.
This model for the structure decay with time at constant shear rate
assumes nth order kinetics for the decay of the material structure with
a rate constant.
Abstract: As one of the convenient and noninvasive sensing
approaches, the automatic limb girth measurement has been applied
to detect intention behind human motion from muscle deformation.
The sensing validity has been elaborated by preliminary researches
but still need more fundamental studies, especially on kinetic
contraction modes. Based on the novel fabric strain sensors, a soft
and smart limb girth measurement system was developed by the
authors’ group, which can measure the limb girth in-motion.
Experiments were carried out on elbow isometric flexion and elbow
isokinetic flexion (biceps’ isokinetic contractions) of 90°/s, 60°/s, and
120°/s for 10 subjects (2 canoeists and 8 ordinary people). After
removal of natural circumferential increments due to elbow position,
the joint torque is found not uniformly sensitive to the limb
circumferential strains, but declining as elbow joint angle rises,
regardless of the angular speed. Moreover, the maximum joint torque
was found as an exponential function of the joint’s angular speed.
This research highly contributes to the application of the automatic
limb girth measuring during kinetic contractions, and it is useful to
predict the contraction level of voluntary skeletal muscles.
Abstract: Both steady and unsteady turbulent mixed convection
heat transfer in a 3D lid-driven enclosure, which has constant heat
flux on the middle of bottom wall and with isothermal moving
sidewalls, is reported in this paper for working fluid with Prandtl
number Pr = 0.71. The other walls are adiabatic and stationary. The
dimensionless parameters used in this research are Reynolds number,
Re = 5000, 10000 and 15000, and Richardson number, Ri = 1 and 10.
The simulations have been done by using different turbulent methods
such as RANS, URANS, and LES. The effects of using different k-ε
models such as standard, RNG and Realizable k-ε model are
investigated. Interesting behaviours of the thermal and flow fields
with changing the Re or Ri numbers are observed. Isotherm and
turbulent kinetic energy distributions and variation of local Nusselt
number at the hot bottom wall are studied as well. The local Nusselt
number is found increasing with increasing either Re or Ri number.
In addition, the turbulent kinetic energy is discernibly affected by
increasing Re number. Moreover, the LES results have shown good
ability of this method in predicting more detailed flow structures in
the cavity.
Abstract: In this work, our goal is to optimize the nitriding treatment at a low-temperature of the steel 32CrMoV13 using gas mixtures of ammonia, nitrogen and hydrogen to improve the mechanical properties of the surface (good wear resistance, friction and corrosion), and of the diffusion layer of the nitrogen (good resistance to fatigue and good tenacity with heart). By limiting our work to the pure iron and to the alloys iron-chromium and iron-chromium-carbon, we have studied the various parameters which manage the nitriding: flow rate and composition of the gaseous phase, the interaction chromium-nitrogen and chromium-carbon by the help of experiments of nitriding realized in the laboratory by thermogravimetry. The acquired knowledge has been applied by the mastery of the growth of the γ' combination layer on the α diffusion layer in the case of the industrial steel 32CrMoV13.
Abstract: In order to investigate the prebiotic potential of
oligosaccharides prepared by chemical hydrolysis of water-soluble
polysaccharides (WSP) from Zizyphus lotus leaves, the effect of
oligosaccharides on bacterial growth was studied. The chemical
composition of WSP was evaluated by colorimetric assays revealed
the average values: 7.05±0.73% proteins and 86.21±0.74%
carbohydrates, among them 64.81±0.42% is neutral sugar and the rest
16.25±1.62% is uronic acids. The characterization of
monosaccharides was determined by high performance anion
exchange chromatography with pulsed amperometric detection
(HPAEC-PAD) was found to be composed of galactose (23.95%),
glucose (21.30%), rhamnose (20.28%), arabinose (9.55%), and
glucuronic acid (22.95%). The effects of oligosaccharides on the
growth of lactic acid bacteria were compared with those of fructooligosaccharide
(RP95). The oligosaccharides concentration was
1g/L of Man, Rogosa, Sharpe broth. Bacterial growth was assessed
during 2, 4.5, 6.5, 9, 12, 16 and 24 h by measuring the optical density
of the cultures at 600 nm (OD600) and pH values. During
fermentation, pH in broth cultures decreased from 6.7 to 5.87±0.15.
The enumeration of lactic acid bacteria indicated that
oligosaccharides led to a significant increase in bacteria (P≤0.05)
compared to the control. The fermentative metabolism appeared to be
faster on RP95 than on oligosaccharides from Zizyphus lotus leaves.
Both RP95 and oligosaccharides showed clear prebiotic effects, but
had differences in fermentation kinetics because of to the different
degree of polymerization. This study shows the prebiotic
effectiveness of oligosaccharides, and provides proof for the selection
of leaves of Zizyphus lotus for use as functional food ingredients.
Abstract: Recovering resources from water purification sludge
(WPS) have been gradually stipulated in environmental protection
laws and regulations in many nations. Hence, reusing the WPS is
becoming an important topic, and recovering alum from WPS is one of
the many practical alternatives. Most previous research efforts have
been conducted on studying the amphoteric characteristic of aluminum
hydroxide for investigating the optimum pH range to dissolve the
Al(III) species from WPS, but it has been lack of reaction kinetics or
mechanisms related discussion. Therefore, in this investigation, water
purification sludge (WPS) solution was broken by ultrasound to make
particle size of reactants smaller, specific surface area larger.
According to the reaction kinetics, these phenomena let the dissolved
aluminum salt quantity increased and the reaction rate go faster.
Abstract: The increase of technogenic and natural accidents,
accompanied by air pollution, for example, by combustion products,
leads to the necessity of respiratory protection. This work is devoted to the development of a calorimetric method
and a device which allows investigating quickly the kinetics of
carbon dioxide sorption by chemisorbents on the base of potassium
superoxide in order to assess the protective properties of respiratory
protective closed circuit apparatus. The features of the traditional approach for determining the
sorption properties in a thin layer of chemisorbent are described, as
well as methods and devices, which can be used for the sorption
kinetics study. The authors developed an approach (as opposed to the traditional
approach) based on the power measurement of internal heat sources
in the chemisorbent layer. The emergence of the heat sources is a
result of exothermic reaction of carbon dioxide sorption. This
approach eliminates the necessity of chemical analysis of samples
and can significantly reduce the time and material expenses during
chemisorbents testing. Error of determining the volume fraction of adsorbed carbon
dioxide by the developed method does not exceed 12%. Taking into
account the efficiency of the method, we consider that it is a good
alternative to traditional methods of chemical analysis under the
assessment of the protection sorbents quality.
Abstract: Polycyclic Aromatic Hydrocarbons (PAHs) are
formed mainly because of incomplete combustion of organic
materials during industrial, domestic activities or natural occurrence.
Their toxicity and contamination of terrestrial and aquatic ecosystem
have been established. However, with limited validity index, previous
research has focused on PAHs isomer pair ratios of variable
physicochemical properties in source identification. The objective of
this investigation was to determine the empirical validity of Pearson
Correlation Coefficient (PCC) and Cluster Analysis (CA) in PAHs
source identification along soil samples of different land uses.
Therefore, 16 PAHs grouped, as Endocrine Disruption Substances
(EDSs) were determined in 10 sample stations in top and sub soils
seasonally. PAHs was determined the use of Varian 300 gas
chromatograph interfaced with flame ionization detector. Instruments
and reagents used are of standard and chromatographic grades
respectively. PCC and CA results showed that the classification of
PAHs along pyrolitic and petrogenic organics used in source
signature is about the predominance PAHs in environmental matrix.
Therefore, the distribution of PAHs in the studied stations revealed
the presence of trace quantities of the vast majority of the sixteen
PAHs, which may ultimately inhabit the actual source signature
authentication. Therefore, factors to be considered when evaluating
possible sources of PAHs could be; type and extent of bacterial
metabolism, transformation products/substrates, and environmental
factors such as salinity, pH, oxygen concentration, nutrients, light
intensity, temperature, co-substrates, and environmental medium are
hereby recommended as factors to be considered when evaluating
possible sources of PAHs.
Abstract: The objective of this study was to synthesize and
characterize the poly(alkenoic acid)s with different molecular
structures, use these polymers to formulate a dental cement
restorative, and study the effect of molecular structures on reaction
kinetics, viscosity, and mechanical strengths of the formed polymers
and cement restoratives. In this study, poly(alkenoic acid)s with
different molecular structures were synthesized. The purified
polymers were formulated with commercial Fuji II LC glass fillers to
form the experimental cement restoratives. The reaction kinetics was
studied via 1HNMR spectroscopy. The formed restoratives were
evaluated using compressive strength, diametral tensile strength,
flexural strength, hardness and wear-resistance tests. Specimens were
conditioned in distilled water at 37oC for 24 h prior to testing. Fuji II
LC restorative was used as control. The results show that the higher
the arm number and initiator concentration, the faster the reaction
was. It was also found that the higher the arm number and branching
that the polymer had, the lower the viscosity of the polymer in water
and the lower the mechanical strengths of the formed restorative. The
experimental restoratives were 31-53% in compressive strength, 37-
55% in compressive modulus, 80-126% in diametral tensile strength,
76-94% in flexural strength, 4-21% in fracture toughness and 53-96%
in hardness higher than Fuji II LC. For wear test, the experimental
restoratives were only 5.4-13% of abrasive and 6.4-12% of attritional
wear depths of Fuji II LC in each wear cycle. The aging study also
showed that all the experimental restoratives increased their strength
continuously during 30 days, unlike Fuji II LC. It is concluded that
polymer molecular structures have significant and positive impact on
mechanical properties of dental cement restoratives.
Abstract: Wicking and evaporation of water in porous knitted fabrics is investigated by combining experimental and analytical approaches: The standard wicking model from Lucas and Washburn is enhanced to account for evaporation and gravity effects. The goal is to model the effect of gravity and evaporation on wicking using simple analytical expressions and investigate the influence of fabrics geometrical parameters, such as porosity and thickness on evaporation impact on maximum reachable height values. The results show that fabric properties have a significant influence on evaporation effect. In this paper, an experimental study of determining water kinetics from different knitted fabrics were gravimetrically investigated permitting the measure of the mass and the height of liquid rising in fabrics in various atmospheric conditions. From these measurements, characteristic pore parameters (capillary radius and permeability) can be determined.
Abstract: High moisture content in fruits generates post-harvest
problems such as mechanical, biochemical, microbial and physical
losses. Dehydration, which is based on the reduction of water activity
of the fruit, is a common option for overcoming such losses.
However, regular hot air drying could affect negatively the quality
properties of the fruit due to the long residence time at high
temperature. Power ultrasound (US) application during the
convective drying has been used as a novel method able to enhance
drying rate and, consequently, to decrease drying time. In the present
study, a new approach was tested to evaluate the effect of US on the
drying time, the final antioxidant activity (AA) and the total
polyphenol content (TPC) of banana slices (BS), mango slices (MS)
and guava slices (GS). There were also studied the drying kinetics
with nine different models from which water effective diffusivities
(Deff) (with or without shrinkage corrections) were calculated.
Compared with the corresponding control tests, US assisted drying
for fruit slices showed reductions in drying time between 16.23 and
30.19%, 11.34 and 32.73%, and 19.25 and 47.51% for the MS, BS
and GS respectively. Considering shrinkage effects, Deff calculated
values ranged from 1.67*10-10 to 3.18*10-10 m2/s, 3.96*10-10 and
5.57*10-10 m2/s and 4.61*10-10 to 8.16*10-10 m2/s for the BS, MS and
GS samples respectively. Reductions of TPC and AA (as DPPH)
were observed compared with the original content in fresh fruit data
in all kinds of drying assays.
Abstract: Ocean current is always available around the
surrounding of SHELL Sabah Water Platform and data are collected
every 10 minutes, 24 hours a day, for a period of 365 days. Due to
low current speed, conventional hydrokinetic power generation is not
feasible, thus leading to the study of low current enabled vortex
induced vibration power generation application. In this case, the
design of a vortex induced vibration application is studied to obtain
an optimum design for the VIV oscillator. Power output is then
determined to study the feasibility of the VIV application in low
current condition.
Abstract: The aim of this study was to investigate the
photocatalytic activity of polycrystalline phases of bismuth tungstate
of formula Bi2WO6. Polycrystalline samples were elaborated using a
coprecipitation technique followed by a calcination process at
different temperatures (300, 400, 600 and 900°C). The obtained
polycrystalline phases have been characterized by X-ray diffraction
(XRD), scanning electron microscopy (SEM), and transmission
electron microscopy (TEM). Crystal cell parameters and cell volume
depend on elaboration temperature. High-resolution electron
microscopy images and image simulations, associated with X-ray
diffraction data, allowed confirming the lattices and space groups
Pca21. The photocatalytic activity of the as-prepared samples was
studied by irradiating aqueous solutions of Rhodamine B, associated
with Bi2WO6 additives having variable crystallite sizes. The
photocatalytic activity of such bismuth tungstates increased as the
crystallite sizes decreased. The high specific area of the
photocatalytic particles obtained at 300°C seems to condition the
degradation kinetics of RhB.
Abstract: Oxygen Reduction Reaction (ORR) performance of
iron and nitrogen co-doped porous carbon nanoparticles (Fe-NPC)
with various physical and (electro) chemical properties have been
investigated. Fe-NPC nanoparticles are synthesized via a facile
soft-templating procedure by using Iron (III) chloride hexa-hydrate as
iron precursor and aminophenol-formaldehyde resin as both carbon
and nitrogen precursor. Fe-NPC nanoparticles shows high surface area
(443.83 m2g-1), high pore volume (0.52 m3g-1), narrow mesopore size
distribution (ca. 3.8 nm), high conductivity (IG/ID=1.04), high kinetic
limiting current (11.71 mAcm-2) and more positive onset potential
(-0.106 V) compared to metal-free NPC nanoparticles (-0.295V)
which make it high efficient ORR metal-free catalysts in alkaline
solution. This study may pave the way of feasibly designing iron and
nitrogen containing carbon materials (Fe-N-C) for highly efficient
oxygen reduction electro-catalysis.
Abstract: Anammox is a novel and promising technology that has changed the traditional concept of biological nitrogen removal. The process facilitates direct oxidation of ammonical nitrogen under anaerobic conditions with nitrite as an electron acceptor without addition of external carbon sources. The present study investigated the feasibility of Anammox Hybrid Reactor (AHR) combining the dual advantages of suspended and attached growth media for biodegradation of ammonical nitrogen in wastewater. Experimental unit consisted of 4 nos. of 5L capacity AHR inoculated with mixed seed culture containing anoxic and activated sludge (1:1). The process was established by feeding the reactors with synthetic wastewater containing NH4-H and NO2-N in the ratio 1:1 at HRT (hydraulic retention time) of 1 day. The reactors were gradually acclimated to higher ammonium concentration till it attained pseudo steady state removal at a total nitrogen concentration of 1200 mg/l. During this period, the performance of the AHR was monitored at twelve different HRTs varying from 0.25-3.0 d with increasing NLR from 0.4 to 4.8 kg N/m3d. AHR demonstrated significantly higher nitrogen removal (95.1%) at optimal HRT of 1 day. Filter media in AHR contributed an additional 27.2% ammonium removal in addition to 72% reduction in the sludge washout rate. This may be attributed to the functional mechanism of filter media which acts as a mechanical sieve and reduces the sludge washout rate many folds. This enhances the biomass retention capacity of the reactor by 25%, which is the key parameter for successful operation of high rate bioreactors. The effluent nitrate concentration, which is one of the bottlenecks of anammox process was also minimised significantly (42.3-52.3 mg/L). Process kinetics was evaluated using first order and Grau-second order models. The first-order substrate removal rate constant was found as 13.0 d-1. Model validation revealed that Grau second order model was more precise and predicted effluent nitrogen concentration with least error (1.84±10%). A new mathematical model based on mass balance was developed to predict N2 gas in AHR. The mass balance model derived from total nitrogen dictated significantly higher correlation (R2=0.986) and predicted N2 gas with least error of precision (0.12±8.49%). SEM study of biomass indicated the presence of heterogeneous population of cocci and rod shaped bacteria of average diameter varying from 1.2-1.5 mm. Owing to enhanced NRE coupled with meagre production of effluent nitrate and its ability to retain high biomass, AHR proved to be the most competitive reactor configuration for dealing with nitrogen laden wastewater.
Abstract: Tannase (tannin acyl hydrolase, E.C.3.1.1.20) is an
important hydrolysable enzyme with innumerable applications and
industrial potential. In the present study, a kinetic model has been
developed for the batch fermentation used for the production of
tannase by A.flavus MTCC 3783. Maximum tannase activity of
143.30 U/ml was obtained at 96 hours under optimum operating
conditions at 35oC, an initial pH of 5.5 and with an inducer tannic
acid concentration of 3% (w/v) for a fermentation period of 120
hours. The biomass concentration reaches a maximum of 6.62 g/l at
96 hours and further there was no increase in biomass concentration
till the end of the fermentation. Various unstructured kinetic models
were analyzed to simulate the experimental values of microbial
growth, tannase activity and substrate concentration. The Logistic
model for microbial growth , Luedeking - Piret model for production
of tannase and Substrate utilization kinetic model for utilization of
substrate were capable of predicting the fermentation profile with
high coefficient of determination (R2) values of 0.980, 0.942 and
0.983 respectively. The results indicated that the unstructured models
were able to describe the fermentation kinetics more effectively.