Shakeel Khan - Profile on Academia.edu (original) (raw)

Papers by Shakeel Khan

New Biotechnology, 2009

Fungal cellulases are well-studied enzymes and are used in various industrial processes. Much of ... more Fungal cellulases are well-studied enzymes and are used in various industrial processes. Much of the knowledge of enzymatic depolymerization of cellulosic material has come from Trichoderma cellulase system. Species of Trichoderma can produce substantial amounts of endoglucanase and exoglucanase but very low levels of b-glucosidase. This deficiency necessitates screening of fungi for cellulytic potential. A number of indigenously isolated fungi were screened for cellulytic potential. In the present study, the kinetics of cellulase production from an indigenous strain of Aspergillus niger MS82 is reported. Product formation parameters of endoglucanase and b-glucosidase (Q p + Y p/s ) indicate that A. niger MS82 is capable of producing moderate to high levels of both endoglucanase and b-glucosidase when grown on different carbon containing natural substrates, for example, grass, corncob, bagasse along side purified celluloses. Furthermore, it was observed that the production of endoglucanase reaches its maximum during exponential phase of growth, while b-glucosidase during the Stationary phase. Enzyme production by solid-state fermentation was also investigated and found to be promising. Highest production of cellulase was noted at pH 4.0 at 35 8C under submerged conditions. Growth and enzyme production was affected by variations in temperature and pH.

Ferromagnetism and adiabatic to non-adiabatic switching process in La0.33Sr0.67Mn1−xFexO3 (0≤x≤0.02) manganite

Journal of Magnetism and Magnetic Materials, 2014

ABSTRACT We have systematically investigated structural, electrical and magnetic properties of Fe... more ABSTRACT We have systematically investigated structural, electrical and magnetic properties of Fe doped La0.33Sr0.67MnO3 manganites synthesized through solid-state reaction-route. All the samples are found to have rhombohedral crystal structure. The crystallite sizes obtained by XRD data are much smaller than the average grain size obtained by scanning electron microscope (SEM). Temperature dependent resistivity data were fitted using Mott׳s variable-range hopping (VRH) and small polaron hopping (SPH) models for obtaining different parameters. The adiabatic SPH conduction mechanism is followed almost for both samples in the absence of magnetic field but a switching from adiabatic to non-adiabatic SPH conduction mechanism is found in the presence of magnetic field. Temperature dependent magnetization (M–T) measurements confirm the decrease in Curie-temperature (TC) with Fe doping. Both the samples exhibited ferromagnetic behavior at 10 K and 300 K with a small hysteresis loop and low coercivity.

Influence of Mn Doping on Structural, Optical, Dielectric and Electrical Properties of ZnO Nanostructures

Journal of Nanoengineering and Nanomanufacturing, 2012

ABSTRACT Nanocrystalline samples of Zn1-xMnxO (0 ≤ x ≤ 0.10) have been prepared by sol-gel route.... more ABSTRACT Nanocrystalline samples of Zn1-xMnxO (0 ≤ x ≤ 0.10) have been prepared by sol-gel route. The synthesized samples were characterized by X-ray diffraction (XRD), SEM, EDX, UV–Vis, temperature dependent resistivity and dielectric properties at room temperature in the frequency range of 42 Hz to 5 MHz. XRD studies exhibited wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) for all samples. The average crystallite size was calculated from XRD data lies within the range 23-27 nm. The SEM micrographs show the agglomeration of the nanoparticles. The UV–Vis. measurement shows reduction in the band gap by Mn doping upto 3% and further it increases for the higher doping of Mn. The dielectric constant (ε), loss tangent (tanδ) and ac conductivity (σac) were studied as a function of frequency and composition at room temperature. The experimental results showed that ε and tanδ decrease when the frequency increases while σac increases with variation in frequency. This behavior can be explained on the basis of space charge polarization according to Maxwell and Wagner’s two-layer model. Resistivity measurement shows semiconducting behavior for all samples.

Temperature-dependent dielectric and magnetic properties of Mn doped zinc oxide nanoparticles

Materials Science in Semiconductor Processing, 2014

ABSTRACT Mn substituted zinc oxide (ZnO) nanoparticles with general formula Zn1−xMnxO (x=0.0, 0.0... more ABSTRACT Mn substituted zinc oxide (ZnO) nanoparticles with general formula Zn1−xMnxO (x=0.0, 0.03, 0.05 and 0.10) were synthesized through a sol-gel route. The result of x-ray diffraction (XRD) analysis confirms the presence of wurtzite crystal structure for all samples suggested that doped Mn ions are occupying regular Zn sites. Transmission electron microscopy (TEM) images exhibit the growth of particle size in the range of 30-50 nm. The results of dielectric measurement indicate that the parameters ε′, ε″, tanδ and σac are decreasing with the increase in frequency; whereas these parameters increase with the increase in temperature. Dielectric parameters are also found to increase with the increase in Mn concentration up to 5%, beyond this value the parameters become lower. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell and Wagner’s two-layer model and the hopping between adjacent Mn2+ and Mn3+ ions. The analysis of temperature dependant magnetization data gives the idea about ferromagnetic (FM) exchange interaction.

STRUCTURAL AND MAGNETIC PROPERTIES OF La 0.67 Sr 0.33 Mn 0.93 Zn 0.07 O 3 MANGANITE

International Journal of Modern Physics: Conference Series, 2013

ABSTRACT The structural and magnetic measurements have been carried out on La0.67Sr0.33Mn0.93Zn0.... more ABSTRACT The structural and magnetic measurements have been carried out on La0.67Sr0.33Mn0.93Zn0.07O3 (LSMZO) polycrystalline sample. The sample has been prepared through Sol-Gel route. X-ray diffraction (XRD) pattern confirms the single phase nature of the sample with orthorhombic crystal symmetry. Field dependent magnetization shows the hysteresis loop with very low coercive field and the magnetization does not saturate up to the field of 5000 gauss in magnitude.

Optical Materials, 2013

and sharing with colleagues.

Thin film of Cobalt Ferrite was deposited on Si (1 0 0) substrate using Pulsed Laser Deposition (... more Thin film of Cobalt Ferrite was deposited on Si (1 0 0) substrate using Pulsed Laser Deposition (PLD) technique. The deposited film was characterized by X-ray Diffraction (XRD), X-ray reflectivity (XRR), Rutherford Backscattering Spectroscopy (RBS) and Raman Spectroscopy and was found to be single phase, textured along (1 1 1) directions and approximately matching the stoichoimetry of the target with negligible strain. The film had a very uniform and flat surface. Raman spectroscopy measurement further confirmed the formation of single phase cubic spinel structure. T 2g Raman mode was missing from the spectra which may be due to cation redistribution and crystallite size effect.

Structural and dielectric properties of Mn doped copper oxide (CuO) nanostructure

ABSTRACT Undoped and Mn doped CuO nanocrystalline powder samples were prepared through standard s... more ABSTRACT Undoped and Mn doped CuO nanocrystalline powder samples were prepared through standard solid state reaction method. The crystal structures of the CuO nanoparticles were characterized by X-ray diffraction. Dielectric measurements were performed on samples as a function of frequency at room temperate to determine the dielectric behavior of the samples. XRD data exhibited the presence of monoclinic crystal structure similar to the parent compound in all samples, suggesting that doped Mn ions sit at the regular lattice sites. The average crystallite size, calculated using Scherrer formula from XRD data, is found within the range of 23-27 nm. The dielectric constant (��), imaginary part of dielectric constant (��) and loss tangent (tan�) were studied as a function of frequency and composition at room temperature. The dependence of dielectric ��������� ������ ��������� ��������������������������������in terms of hopping. This behavior can be explained on the basis of space charge pola��������������������������� ����� �����������-layer model.

Journal of Materials Science: Materials in Electronics, 2011

In this paper, the structural and dielectric properties of BNO (BiNbO 4 ) was investigated as a f... more In this paper, the structural and dielectric properties of BNO (BiNbO 4 ) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and 10 wt. % Bi 2 O 3 -PbO were sintered at 1,025°C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the triclinic phase (b-BNO). In the measurements obtained at room temperature (25°C) was observed that the largest values of dielectric permittivity (e 0 r ) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi 2 O 3 ) and BNO5Pb (5 wt. % PbO) with values e 0 r * 59.54 and e 0 r * 78.44, respectively. The smaller values of loss tangent (tan d) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with values tan d * 5.71 9 10 -4 and tan d * 2.19 9 10 -4 , respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples, obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about e 0 r * 76.4 at temperature 200°C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at temperature 80°C, with about tan d * 5.4 9 10 -3 . The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (-55.06 ppm/°C) to the sample doped of Bi: BNO3Bi (?86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (?208.87 ppm/°C). One can conclude that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C, which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H) obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be studied seeking the development ceramic capacitors for applications in radio frequency devices.

Journal of Applied Physics, 2012

Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range ... more Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range J. Appl. Phys. 112, 094104 (2012) Gate stack dielectric degradation of rare-earth oxides grown on high mobility Ge substrates J. Appl. Phys. 112, 094501 (2012) Solvated dissipative electro-elastic network model of hydrated proteins JCP: BioChem. Phys. 6, 10B620 Solvated dissipative electro-elastic network model of hydrated proteins J. Chem. Phys. 137, 165101 (2012) Experimental studies of Debye-like process and structural relaxation in mixtures of 2-ethyl-1-hexanol and 2-ethyl-1-hexyl bromide Nanoparticles of CoFe 2 O 4 and CoIn 0.15 Fe 1.85 O 4 ferrites were prepared by citrate gel route and characterized to understand their structural, electrical, and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase cubic spinel structure. The average grain sizes from the Scherrer formula were below 50 nm. Microstructural features were obtained by scanning electron microscope and compositional analysis by energy dispersive spectroscopy. The hysteresis curve shows enhancement in coercivity while reduction in saturation magnetization with the substitution of In 3þ ions. Enhancement of coercivity is attributed to the transition from multidomain to single domain nature. Electrical properties, such as dc resistivity as a function of temperature and ac conductivity as a function of frequency and temperature were studied for both the samples. The activation energy derived from the Arrhenius equation was found to increase in the doped sample. The dielectric constant (e 0 ) and dielectric loss (tan d) are also studied as a function of frequency and temperature. The variation of dielectric properties e 0 , tan d, and ac conductivity (r ac ) with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization in general and the hopping of charge between Fe 2þ and Fe 3þ as well as between Co 2þ and Co 3þ ions at B-sites. Magnetization and electrical property study showed its dominant dependence on the grain size. V C 2012 American Institute of Physics.

Adiabatic to non adiabatic change in conduction mechanism of Zn doped La0.67Sr0.33MnO3 perovskite

Journal of Alloys and Compounds, 2013

ABSTRACT We reported the results of electrical transport properties of La0.67Sr0.33Mn1−xZnxO3 (x ... more ABSTRACT We reported the results of electrical transport properties of La0.67Sr0.33Mn1−xZnxO3 (x = 0.1 and 0.2) bulk samples prepared by solid-state reaction route over a wide temperature range from 5 to 300 K in the presence of magnetic fields. Powder X-ray diffraction patterns at room temperature confirmed that both samples were formed in a single phase. Temperature dependent resistivity data were fitted using Mott’s variable-range hopping (VRH) model for a limited range of temperatures (from 235.5 to 300 K for 10% Zn doped and from 133 to 300 K for 20% Zn doped samples) to calculate the hopping distance (Rh) and the density of states near the Fermi level, [N(EF)]. It was found that all the parameters vary systematically with the increase in Zn concentration. Moreover, the temperature dependent resistivity data were also fitted using the small polaron hopping (SPH) model. The adiabatic SPH conduction is followed for 10% doped sample at all fields while a non-adiabatic SPH conduction is found to be active for 20% doped sample in all fields. This type of change in the conduction mechanism is accompanied by subtle electronically induced structural changes involving Mn–O–Mn and Zn–O–Mn bond angles and bond lengths. Thus, we suggest that the transport properties can be explained according to the additional delocalization of charge carriers induced by Zn doping.

Journal of Alloys and Compounds, 2012

The structural, electrical and magnetic properties have been investigated on La 0.67 Sr 0.33 Mn 1... more The structural, electrical and magnetic properties have been investigated on La 0.67 Sr 0.33 Mn 1−x Zn x O 3 (x = 0.1 and 0.2) system. The samples have been prepared through the conventional solid-state reaction route. All the prepared samples were found in single phase with orthorhombic crystal structure. The crystallite sizes were estimated through X-ray diffraction (XRD) using the Debye-Scherrer's formula. Temperature dependent resistivity data shows metal to semiconducting (M-S) transition for both samples. Magnetization measurements confirm that the Curie-temperature (T C ) is found to decrease with Zn doping. The reduction in T C is attributed to the fact that the double-exchange interaction between Mn 3+ -O 2− -Mn 4+ network has been destroyed by the substitution of Zn at Mn-site.

: The effect of pH of the medium and temperature of incubation was studied on motility of four st... more : The effect of pH of the medium and temperature of incubation was studied on motility of four strains of 2 Listeria species. All the strains were found to be non-motile at pH 4. The motility was observed at a pH range of 5.5 to 9.0. However, the optimum pH and temperature for motility was 7.0 and 22°C respectively. The strains NCTC 7973 and C-274 were, however, motile at pH 5.0. At pH 10, NCTC 5214 m, C-274 and NCTC 7973 were motile at 22°C with the exception of C-274 which was motile also at 35°C. NCTC 5214 m was motile at pH 11 only at 22°C whereas C-274 was motile at both 22 and 35°C. Key Words: Listeria, pH. 28 Microbiology INTRODUCTION The members of the genus Listeria are pathogenic to a very wide range of animals (6, 7) causing multiple clinical manifestations including abortion or still birth in pregnant farm animals (1, 8, 9, 12-17). Listeria that has previously been placed as a member of the family Corynebacteriaceae (2) has now been classified with "Erysipelothrix&q...

Synthesis of alkyl catechols and evaluation of their antibacterial and cyfotoxic activity

Pakistan journal of pharmaceutical sciences

A series of potential biologically active mono-, di- and tetra- alkyl catechols were prepared thr... more A series of potential biologically active mono-, di- and tetra- alkyl catechols were prepared through Friedel- Crafts alkylation of catechol, and evaluated for their antibacterial and cytotoxic activity. The mono-substituted alkyl derivatives showed maximum antibacterial activity in vitro which increased with the increasing length of the alkyl chains. Primary screening results indicated that all the monoalkyl derivatives except 4- (2-octyl) catechol inhibited the growth of B. bronchoseptica and maximum zones of inhibition were observed in case of monohexyl catechols (both n- and 2-hexyl) and monobenzyl derivative. In case of Gram-negative organisms growth of Kl. pneumoniae and A. calcoaceticus was inhibited by several derivatives. Mono-3-octyl-, monononyl- and monobenzyl catechols markedly inhibited the growth of Kl. pneumoniae. Mono-2-heptyl catechol inhibited the growth of six Gram-negative bacteria. Minimum inhibitory concentration of six most active compounds of the series was d...

Pakistan journal of pharmaceutical sciences

Four different phenacyl-thiosemicarbazone compounds were studied for their antibacterial activity... more Four different phenacyl-thiosemicarbazone compounds were studied for their antibacterial activity against seventeen different species/strains. Of the four compounds under study, O-methoxy- phenacyl-thiosemicarbazone was found to be highly active against almost all the cultures under study. The other compounds were also found to possess antibacterial spectrum, but in very high concentrations for some of the cultures.

Pakistan Journal of Botany

Xylanolytic and cellulolytic potential of a soil isolate, Aspergillus fumigatus (MS16) was studie... more Xylanolytic and cellulolytic potential of a soil isolate, Aspergillus fumigatus (MS16) was studied by growing it on a variety of lignocellulosics, purified cellulose and xylan supplemented media. It was noted that carboxymethyl cellulose, salicin and xylan induce the production of endoglucanase, β-glucosidase and xylanase, respectively. The study revealed that Aspergillus fumigatus (MS16) co-secretes xylanase and cellulase in the presence of xylan; the ratio of the two enzymes was influenced by the initial pH of the medium. The maximum titers of xylanase and cellulase were noted at initial pH of 5.0. Relatively higher titers of both the enzymes were obtained when the fungus was cultivated at 35 o C. Whereas, cellulase production was not detected when the fungus was cultivated at 40 o C. The volumetric productivity (Q p) of xylanase was much higher than cellulases. The organism produced 2-3 folds higher titers of xylanase when grown on lignocellulosic materials in submerged cultivati...

Comparative study on cellulase production

Three strains of Aspergillus niger were retrieved from culture collection of the Department of Mi... more Three strains of Aspergillus niger were retrieved from culture collection of the Department of Microbiology, University of Karachi, Karachi, Pakistan and were studied for their ability to produce cellulases. Cultivation at different temperatures and in presence of various carbon sources revealed that all the three strains produced more amounts of endoglucanase, βglucosidase and filter-paperase activities at 35 o C; carboxymethyl cellulose promotes the production of filter paperase and endoglucanase activities whereas salicin induced β-glucosidase activity. Experiments on growth and enzyme production kinetics showed that generation time and hence volumetric rate of biomass production is influenced by the carbon source used in the medium; simple carbon source, such as glucose favored the growth of all the strains. Cellulases from all the strains showed optimum activity at temperature >50 o C and under acidic range of pH, while melting temperature was 64-65 o C. These findings affirm that cellulases from A. niger are potential candidates as alternative to Trichoderma cellulases.

New Biotechnology, 2009

Fungal cellulases are well-studied enzymes and are used in various industrial processes. Much of ... more Fungal cellulases are well-studied enzymes and are used in various industrial processes. Much of the knowledge of enzymatic depolymerization of cellulosic material has come from Trichoderma cellulase system. Species of Trichoderma can produce substantial amounts of endoglucanase and exoglucanase but very low levels of b-glucosidase. This deficiency necessitates screening of fungi for cellulytic potential. A number of indigenously isolated fungi were screened for cellulytic potential. In the present study, the kinetics of cellulase production from an indigenous strain of Aspergillus niger MS82 is reported. Product formation parameters of endoglucanase and b-glucosidase (Q p + Y p/s ) indicate that A. niger MS82 is capable of producing moderate to high levels of both endoglucanase and b-glucosidase when grown on different carbon containing natural substrates, for example, grass, corncob, bagasse along side purified celluloses. Furthermore, it was observed that the production of endoglucanase reaches its maximum during exponential phase of growth, while b-glucosidase during the Stationary phase. Enzyme production by solid-state fermentation was also investigated and found to be promising. Highest production of cellulase was noted at pH 4.0 at 35 8C under submerged conditions. Growth and enzyme production was affected by variations in temperature and pH.

Ferromagnetism and adiabatic to non-adiabatic switching process in La0.33Sr0.67Mn1−xFexO3 (0≤x≤0.02) manganite

Journal of Magnetism and Magnetic Materials, 2014

ABSTRACT We have systematically investigated structural, electrical and magnetic properties of Fe... more ABSTRACT We have systematically investigated structural, electrical and magnetic properties of Fe doped La0.33Sr0.67MnO3 manganites synthesized through solid-state reaction-route. All the samples are found to have rhombohedral crystal structure. The crystallite sizes obtained by XRD data are much smaller than the average grain size obtained by scanning electron microscope (SEM). Temperature dependent resistivity data were fitted using Mott׳s variable-range hopping (VRH) and small polaron hopping (SPH) models for obtaining different parameters. The adiabatic SPH conduction mechanism is followed almost for both samples in the absence of magnetic field but a switching from adiabatic to non-adiabatic SPH conduction mechanism is found in the presence of magnetic field. Temperature dependent magnetization (M–T) measurements confirm the decrease in Curie-temperature (TC) with Fe doping. Both the samples exhibited ferromagnetic behavior at 10 K and 300 K with a small hysteresis loop and low coercivity.

Influence of Mn Doping on Structural, Optical, Dielectric and Electrical Properties of ZnO Nanostructures

Journal of Nanoengineering and Nanomanufacturing, 2012

ABSTRACT Nanocrystalline samples of Zn1-xMnxO (0 ≤ x ≤ 0.10) have been prepared by sol-gel route.... more ABSTRACT Nanocrystalline samples of Zn1-xMnxO (0 ≤ x ≤ 0.10) have been prepared by sol-gel route. The synthesized samples were characterized by X-ray diffraction (XRD), SEM, EDX, UV–Vis, temperature dependent resistivity and dielectric properties at room temperature in the frequency range of 42 Hz to 5 MHz. XRD studies exhibited wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) for all samples. The average crystallite size was calculated from XRD data lies within the range 23-27 nm. The SEM micrographs show the agglomeration of the nanoparticles. The UV–Vis. measurement shows reduction in the band gap by Mn doping upto 3% and further it increases for the higher doping of Mn. The dielectric constant (ε), loss tangent (tanδ) and ac conductivity (σac) were studied as a function of frequency and composition at room temperature. The experimental results showed that ε and tanδ decrease when the frequency increases while σac increases with variation in frequency. This behavior can be explained on the basis of space charge polarization according to Maxwell and Wagner’s two-layer model. Resistivity measurement shows semiconducting behavior for all samples.

Temperature-dependent dielectric and magnetic properties of Mn doped zinc oxide nanoparticles

Materials Science in Semiconductor Processing, 2014

ABSTRACT Mn substituted zinc oxide (ZnO) nanoparticles with general formula Zn1−xMnxO (x=0.0, 0.0... more ABSTRACT Mn substituted zinc oxide (ZnO) nanoparticles with general formula Zn1−xMnxO (x=0.0, 0.03, 0.05 and 0.10) were synthesized through a sol-gel route. The result of x-ray diffraction (XRD) analysis confirms the presence of wurtzite crystal structure for all samples suggested that doped Mn ions are occupying regular Zn sites. Transmission electron microscopy (TEM) images exhibit the growth of particle size in the range of 30-50 nm. The results of dielectric measurement indicate that the parameters ε′, ε″, tanδ and σac are decreasing with the increase in frequency; whereas these parameters increase with the increase in temperature. Dielectric parameters are also found to increase with the increase in Mn concentration up to 5%, beyond this value the parameters become lower. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell and Wagner’s two-layer model and the hopping between adjacent Mn2+ and Mn3+ ions. The analysis of temperature dependant magnetization data gives the idea about ferromagnetic (FM) exchange interaction.

STRUCTURAL AND MAGNETIC PROPERTIES OF La 0.67 Sr 0.33 Mn 0.93 Zn 0.07 O 3 MANGANITE

International Journal of Modern Physics: Conference Series, 2013

ABSTRACT The structural and magnetic measurements have been carried out on La0.67Sr0.33Mn0.93Zn0.... more ABSTRACT The structural and magnetic measurements have been carried out on La0.67Sr0.33Mn0.93Zn0.07O3 (LSMZO) polycrystalline sample. The sample has been prepared through Sol-Gel route. X-ray diffraction (XRD) pattern confirms the single phase nature of the sample with orthorhombic crystal symmetry. Field dependent magnetization shows the hysteresis loop with very low coercive field and the magnetization does not saturate up to the field of 5000 gauss in magnitude.

Optical Materials, 2013

and sharing with colleagues.

Thin film of Cobalt Ferrite was deposited on Si (1 0 0) substrate using Pulsed Laser Deposition (... more Thin film of Cobalt Ferrite was deposited on Si (1 0 0) substrate using Pulsed Laser Deposition (PLD) technique. The deposited film was characterized by X-ray Diffraction (XRD), X-ray reflectivity (XRR), Rutherford Backscattering Spectroscopy (RBS) and Raman Spectroscopy and was found to be single phase, textured along (1 1 1) directions and approximately matching the stoichoimetry of the target with negligible strain. The film had a very uniform and flat surface. Raman spectroscopy measurement further confirmed the formation of single phase cubic spinel structure. T 2g Raman mode was missing from the spectra which may be due to cation redistribution and crystallite size effect.

Structural and dielectric properties of Mn doped copper oxide (CuO) nanostructure

ABSTRACT Undoped and Mn doped CuO nanocrystalline powder samples were prepared through standard s... more ABSTRACT Undoped and Mn doped CuO nanocrystalline powder samples were prepared through standard solid state reaction method. The crystal structures of the CuO nanoparticles were characterized by X-ray diffraction. Dielectric measurements were performed on samples as a function of frequency at room temperate to determine the dielectric behavior of the samples. XRD data exhibited the presence of monoclinic crystal structure similar to the parent compound in all samples, suggesting that doped Mn ions sit at the regular lattice sites. The average crystallite size, calculated using Scherrer formula from XRD data, is found within the range of 23-27 nm. The dielectric constant (��), imaginary part of dielectric constant (��) and loss tangent (tan�) were studied as a function of frequency and composition at room temperature. The dependence of dielectric ��������� ������ ��������� ��������������������������������in terms of hopping. This behavior can be explained on the basis of space charge pola��������������������������� ����� �����������-layer model.

Journal of Materials Science: Materials in Electronics, 2011

In this paper, the structural and dielectric properties of BNO (BiNbO 4 ) was investigated as a f... more In this paper, the structural and dielectric properties of BNO (BiNbO 4 ) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and 10 wt. % Bi 2 O 3 -PbO were sintered at 1,025°C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the triclinic phase (b-BNO). In the measurements obtained at room temperature (25°C) was observed that the largest values of dielectric permittivity (e 0 r ) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi 2 O 3 ) and BNO5Pb (5 wt. % PbO) with values e 0 r * 59.54 and e 0 r * 78.44, respectively. The smaller values of loss tangent (tan d) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with values tan d * 5.71 9 10 -4 and tan d * 2.19 9 10 -4 , respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples, obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about e 0 r * 76.4 at temperature 200°C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at temperature 80°C, with about tan d * 5.4 9 10 -3 . The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (-55.06 ppm/°C) to the sample doped of Bi: BNO3Bi (?86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (?208.87 ppm/°C). One can conclude that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C, which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H) obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be studied seeking the development ceramic capacitors for applications in radio frequency devices.

Journal of Applied Physics, 2012

Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range ... more Dielectric relaxation study of amorphous TiTaO thin films in a large operating temperature range J. Appl. Phys. 112, 094104 (2012) Gate stack dielectric degradation of rare-earth oxides grown on high mobility Ge substrates J. Appl. Phys. 112, 094501 (2012) Solvated dissipative electro-elastic network model of hydrated proteins JCP: BioChem. Phys. 6, 10B620 Solvated dissipative electro-elastic network model of hydrated proteins J. Chem. Phys. 137, 165101 (2012) Experimental studies of Debye-like process and structural relaxation in mixtures of 2-ethyl-1-hexanol and 2-ethyl-1-hexyl bromide Nanoparticles of CoFe 2 O 4 and CoIn 0.15 Fe 1.85 O 4 ferrites were prepared by citrate gel route and characterized to understand their structural, electrical, and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase cubic spinel structure. The average grain sizes from the Scherrer formula were below 50 nm. Microstructural features were obtained by scanning electron microscope and compositional analysis by energy dispersive spectroscopy. The hysteresis curve shows enhancement in coercivity while reduction in saturation magnetization with the substitution of In 3þ ions. Enhancement of coercivity is attributed to the transition from multidomain to single domain nature. Electrical properties, such as dc resistivity as a function of temperature and ac conductivity as a function of frequency and temperature were studied for both the samples. The activation energy derived from the Arrhenius equation was found to increase in the doped sample. The dielectric constant (e 0 ) and dielectric loss (tan d) are also studied as a function of frequency and temperature. The variation of dielectric properties e 0 , tan d, and ac conductivity (r ac ) with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization in general and the hopping of charge between Fe 2þ and Fe 3þ as well as between Co 2þ and Co 3þ ions at B-sites. Magnetization and electrical property study showed its dominant dependence on the grain size. V C 2012 American Institute of Physics.

Adiabatic to non adiabatic change in conduction mechanism of Zn doped La0.67Sr0.33MnO3 perovskite

Journal of Alloys and Compounds, 2013

ABSTRACT We reported the results of electrical transport properties of La0.67Sr0.33Mn1−xZnxO3 (x ... more ABSTRACT We reported the results of electrical transport properties of La0.67Sr0.33Mn1−xZnxO3 (x = 0.1 and 0.2) bulk samples prepared by solid-state reaction route over a wide temperature range from 5 to 300 K in the presence of magnetic fields. Powder X-ray diffraction patterns at room temperature confirmed that both samples were formed in a single phase. Temperature dependent resistivity data were fitted using Mott’s variable-range hopping (VRH) model for a limited range of temperatures (from 235.5 to 300 K for 10% Zn doped and from 133 to 300 K for 20% Zn doped samples) to calculate the hopping distance (Rh) and the density of states near the Fermi level, [N(EF)]. It was found that all the parameters vary systematically with the increase in Zn concentration. Moreover, the temperature dependent resistivity data were also fitted using the small polaron hopping (SPH) model. The adiabatic SPH conduction is followed for 10% doped sample at all fields while a non-adiabatic SPH conduction is found to be active for 20% doped sample in all fields. This type of change in the conduction mechanism is accompanied by subtle electronically induced structural changes involving Mn–O–Mn and Zn–O–Mn bond angles and bond lengths. Thus, we suggest that the transport properties can be explained according to the additional delocalization of charge carriers induced by Zn doping.

Journal of Alloys and Compounds, 2012

The structural, electrical and magnetic properties have been investigated on La 0.67 Sr 0.33 Mn 1... more The structural, electrical and magnetic properties have been investigated on La 0.67 Sr 0.33 Mn 1−x Zn x O 3 (x = 0.1 and 0.2) system. The samples have been prepared through the conventional solid-state reaction route. All the prepared samples were found in single phase with orthorhombic crystal structure. The crystallite sizes were estimated through X-ray diffraction (XRD) using the Debye-Scherrer's formula. Temperature dependent resistivity data shows metal to semiconducting (M-S) transition for both samples. Magnetization measurements confirm that the Curie-temperature (T C ) is found to decrease with Zn doping. The reduction in T C is attributed to the fact that the double-exchange interaction between Mn 3+ -O 2− -Mn 4+ network has been destroyed by the substitution of Zn at Mn-site.

: The effect of pH of the medium and temperature of incubation was studied on motility of four st... more : The effect of pH of the medium and temperature of incubation was studied on motility of four strains of 2 Listeria species. All the strains were found to be non-motile at pH 4. The motility was observed at a pH range of 5.5 to 9.0. However, the optimum pH and temperature for motility was 7.0 and 22°C respectively. The strains NCTC 7973 and C-274 were, however, motile at pH 5.0. At pH 10, NCTC 5214 m, C-274 and NCTC 7973 were motile at 22°C with the exception of C-274 which was motile also at 35°C. NCTC 5214 m was motile at pH 11 only at 22°C whereas C-274 was motile at both 22 and 35°C. Key Words: Listeria, pH. 28 Microbiology INTRODUCTION The members of the genus Listeria are pathogenic to a very wide range of animals (6, 7) causing multiple clinical manifestations including abortion or still birth in pregnant farm animals (1, 8, 9, 12-17). Listeria that has previously been placed as a member of the family Corynebacteriaceae (2) has now been classified with "Erysipelothrix&q...

Synthesis of alkyl catechols and evaluation of their antibacterial and cyfotoxic activity

Pakistan journal of pharmaceutical sciences

A series of potential biologically active mono-, di- and tetra- alkyl catechols were prepared thr... more A series of potential biologically active mono-, di- and tetra- alkyl catechols were prepared through Friedel- Crafts alkylation of catechol, and evaluated for their antibacterial and cytotoxic activity. The mono-substituted alkyl derivatives showed maximum antibacterial activity in vitro which increased with the increasing length of the alkyl chains. Primary screening results indicated that all the monoalkyl derivatives except 4- (2-octyl) catechol inhibited the growth of B. bronchoseptica and maximum zones of inhibition were observed in case of monohexyl catechols (both n- and 2-hexyl) and monobenzyl derivative. In case of Gram-negative organisms growth of Kl. pneumoniae and A. calcoaceticus was inhibited by several derivatives. Mono-3-octyl-, monononyl- and monobenzyl catechols markedly inhibited the growth of Kl. pneumoniae. Mono-2-heptyl catechol inhibited the growth of six Gram-negative bacteria. Minimum inhibitory concentration of six most active compounds of the series was d...

Pakistan journal of pharmaceutical sciences

Four different phenacyl-thiosemicarbazone compounds were studied for their antibacterial activity... more Four different phenacyl-thiosemicarbazone compounds were studied for their antibacterial activity against seventeen different species/strains. Of the four compounds under study, O-methoxy- phenacyl-thiosemicarbazone was found to be highly active against almost all the cultures under study. The other compounds were also found to possess antibacterial spectrum, but in very high concentrations for some of the cultures.

Pakistan Journal of Botany

Xylanolytic and cellulolytic potential of a soil isolate, Aspergillus fumigatus (MS16) was studie... more Xylanolytic and cellulolytic potential of a soil isolate, Aspergillus fumigatus (MS16) was studied by growing it on a variety of lignocellulosics, purified cellulose and xylan supplemented media. It was noted that carboxymethyl cellulose, salicin and xylan induce the production of endoglucanase, β-glucosidase and xylanase, respectively. The study revealed that Aspergillus fumigatus (MS16) co-secretes xylanase and cellulase in the presence of xylan; the ratio of the two enzymes was influenced by the initial pH of the medium. The maximum titers of xylanase and cellulase were noted at initial pH of 5.0. Relatively higher titers of both the enzymes were obtained when the fungus was cultivated at 35 o C. Whereas, cellulase production was not detected when the fungus was cultivated at 40 o C. The volumetric productivity (Q p) of xylanase was much higher than cellulases. The organism produced 2-3 folds higher titers of xylanase when grown on lignocellulosic materials in submerged cultivati...

Comparative study on cellulase production

Three strains of Aspergillus niger were retrieved from culture collection of the Department of Mi... more Three strains of Aspergillus niger were retrieved from culture collection of the Department of Microbiology, University of Karachi, Karachi, Pakistan and were studied for their ability to produce cellulases. Cultivation at different temperatures and in presence of various carbon sources revealed that all the three strains produced more amounts of endoglucanase, βglucosidase and filter-paperase activities at 35 o C; carboxymethyl cellulose promotes the production of filter paperase and endoglucanase activities whereas salicin induced β-glucosidase activity. Experiments on growth and enzyme production kinetics showed that generation time and hence volumetric rate of biomass production is influenced by the carbon source used in the medium; simple carbon source, such as glucose favored the growth of all the strains. Cellulases from all the strains showed optimum activity at temperature >50 o C and under acidic range of pH, while melting temperature was 64-65 o C. These findings affirm that cellulases from A. niger are potential candidates as alternative to Trichoderma cellulases.