共查询到20条相似文献,搜索用时 46 毫秒
1.
There is an abundant literature on calculations of formation and ionization energies of point defects in GaAs. Since most
of these energies, especially the formation energies, are difficult to measure, the calculations are primary means of obtaining
their values. However, based on the assumptions of the calculations, the reported values differ greatly among the various
calculations. In this paper we discuss the sources of errors and their impact on practical predictions valuable in GaAs device
fabrication. In particular, we have compared a large set of computed energies and selected the most appropriate values. Then,
in the context of GaAs material quality, we investigated the impact of errors in calculation of formation energies on the
performance of the GaAs substrate for device fabrication. We find that in spite of the errors inherent in
ab initio
calculations, it is possible to correctly predict the behaviour of GaAs substrate. 相似文献
2.
P. T. Deshmukh D. K. Burghate V. S. Deogaonkar S. P. Yawale S. V. Pakade 《Bulletin of Materials Science》2003,26(6):639-642
The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different
glass compositions in the system (CuO)
x
(PbO)
50−x(Bi2O3)50 (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (Eopt), refractive index (nD), optical dielectric constant (ε′∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have
been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that
a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear
behaviour. The optical parameters were found to be almost the same for different glasses in the same family. 相似文献
3.
The volume variation of the Gruneisen parameters of tenfcc transition metals, up to 40% compression, has been studied on the basis of a model approach proposed by Antonovet al. The results are reasonably good for six metals except for Rh, Ag, Au and Ni when compared with available experimental and
other theoretical values. The model requires an appropriate modification for Rh, Ag, Au and Ni. 相似文献
4.
P. D. Gaikwad D. J. Shirale V. K. Gade P. A. Savale K. P. Kakde H. J. Kharat M. D. Shirsat 《Bulletin of Materials Science》2006,29(4):417-420
The potentiometric study of polyaniline (PANI) film synthesized with dopants viz. polyvinyl sulfonic acid (PVS),p-toluene sulfonic acid (p
TS), dodecyl benzene sulfonic acid (DBS) and composite-dopants viz. PVS-p
TS and PVS-DBS, has been carried out. The synthesized PANI films were characterized by electrochemical technique, UV-visible
spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and conductivity measurement.
It was found that the PANI doped with PVS gives good electrochemical properties, conductivity as well as surface morphology
as compared to
p
TS and DBS, whereas in composite dopants the PANI doped with PVS-pTS gives good polymer matrix as compared to PVS-DBS. 相似文献
5.
6.
Biodegradable polymers represent one of the most significant area of research today. Among these polymers, poly (β-hydroxy
butyrate co β′-hydroxy valerate) i.e. PHBV have received special attention because of their unique combination of properties.
They are perfectly biocompatible, biodegradable polymers and can be processed by any conventional technique. In the present
study an attempt has been made to develop the biodegradable blends of PHBV by blending them with ethyl cellulose (EC). Ethyl
cellulose has been selected to monitor the biodegradation rate of PHBV and also for making the blends cost effective. The
blends are thoroughly characterized for their compatibility, by the measurement of viscosity of blends and through FT-IR.
Various applications of PHBV/EC blend in agriculture and pharmaceutical industries are being explored.
Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore. 相似文献
7.
Sm-Ru intermetallic surface alloy films were prepared by vacuum deposition and annealing of rare earth Sm on single crystal
Ru(0001) surface. The Ru 3
d
and Sm 3
d
core level spectra clearly show the formation of surface alloy layers. XPS measurements on surface alloy film revealed an
induced peak in the Ru 3
d
region at lower binding energy by 1 eV compared to the bulk Ru (elemental) suggesting an electronic effect of alloying and
Sm-Ru bond formation. The Sm 3
d
5/2
photoemission peak of Sm film consists of strong features characteristic of Sm(II) with electron configuration 4
f
6
(5
d
6
s
)
2
and Sm(III) with electron configuration 4
f
5
(5
d
6
s
)
3
.It is observed that the Sm(II) feature decreases in intensity upon alloy formation with surface Ru atoms. Oxidation of these
films with carbon monoxide indicates alloy breakdown due to the oxidation of Sm atoms selectively. Alloy oxidation also shows
a clear shift of Sm 3
d
5/2
feature. 相似文献
8.
Mahesh Thondawada Dhanabal S. Palanisamy Hanumant Singh Rathore Ramesh C. Gupta Pavan Kumar Chintamaneni 《Drug development and industrial pharmacy》2018,44(7):1120-1129
Nanotechnology based biomedical approaches and surface modification techniques made it easier for targeting specific site and improving the treatment efficacy. The present study reports on targeted polymeric nanoparticles conjugated with antibody as a site-specific carrier system for effective treatment of type 1 diabetes. Sitagliptin (SP)-loaded Poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NP) were prepared by nanoprecipitation cum solvent evaporation method and were characterized in terms of morphology, size, surface charge, and entrapment efficiency. Optimized batch demonstrated a particle size of 105.24?nm, with significant entrapment efficacy. In vitro release studies exhibited a controlled release pattern of 67.76?±?1.30% in 24?h, and a maximum of 96.59?±?1.26% at the end of 48?h. Thiol groups were introduced on the surface of SP-NPs whose concentration on SP-NPs was 27?±?2.6?mmol/mol PLGA-NPs, anti-CD4 antibody clone Q4120 was conjugated to the thiolated SP-NPs via a sulfo-MBS cross-linker, ~70% conjugation was observed. The in vitro cytotoxicity studies performed on RIN-5?F cells for mAb-SP-NPs presented an IC50 of 76?µg/mL, and the insulin release assay had revealed an increased release at 5.15?±?0.16?IU/mL. The results indicate that mAb-SP-NPs allowed a controlled release of SP and thereby produced insulin levels comparable with control. Therefore, mAb-SP-NPs system appears to be effective in the treatment of auto immune diabetes, subject to further analysis. 相似文献
9.
Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy 总被引:3,自引:0,他引:3
K. T. Kashyap 《Bulletin of Materials Science》2001,24(6):643-648
It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy.
Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second
phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag.
In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity
by giving ultra fine grain size to the alloy. Addition of zirconium produces Al
3
Zr particles which pin the grain boundaries during recrystallization and grain growth.
In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al
3
Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium.
Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al
3
Zr particles and found to be rod shaped and identified to be cubic ordered
L
1
2
phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al
3
Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth.
It was found that the fine dispersion of Al
3
Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy. 相似文献
10.
S. R. Murthy 《Bulletin of Materials Science》2001,24(6):611-616
Polycrystalline NiZn ferrites with different grain sizes (1.2 (Am to 10.2 (Am) were prepared by the usual ceramic method.
The magnetic properties were measured at room temperature. The ultrasonic velocity and attenuation were measured on Ni-Zn
ferrite by using the pulse transmission method at 1 MHz, in the temperature range 300–600 K. The velocity was found to be
slightly sample dependent at room temperature and decreased with increasing temperature, except near the Curie temperature,
T
c
,where a small anomaly was observed. The longitudinal attenuation (α
1
)at room temperature was found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation
exhibited a broad maximum around 400 K and a sharp maximum just below Curie temperature (
T
c
).The above observations were carried out in the demagnetized state. The application of a 380 mT magnetic field allowed us to
reach the saturated state of the sample at all the measuring temperatures. The anomaly observed in the thermal variation of
velocities (longitudinal and transverse) and attenuation has been qualitatively explained with the help of the temperature
variation of the magneto-crystalline anisotropy constant. 相似文献
11.
B. T. Cong P. N. A. Huy P. K. Schelling J. W. Halley 《Bulletin of Materials Science》2003,26(1):155-158
We present results of numerical computation on some characteristics of BaTiO3 such as total energy, lattice constant, density
of states, band structure etc using self-consistent tight binding method. Besides strong Ti-O bond between 3
d
on titanium and 2
p
orbital on oxygen states, we also include weak hybridization between the Ba 6
s
and O 2
p
tates. The results are compared with those of other more sophisticated methods. 相似文献
12.
B. Eraiah 《Bulletin of Materials Science》2006,29(4):375-378
Glasses with the composition, (Sm2
O
3)
x
(ZnO)(40-x)(TeO
2)(60), were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses
have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz
relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide
ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well
compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been
explained. 相似文献
13.
We present an
ab initio
calculation of interlayer magnetic coupling for Fe/Nb multilayers using the self-consistent full-potential linearized augmented-plane-wave
(FLAPW) method. For this calculation, we have constructed supercells consisting of
bcc
Fe and Nb multilayers in Fe/Nb/Fe sandwich geometry stacked along (001) direction. In the supercells two Fe layers are separated
by Nb layers ranging from 1 to 11 layers. We have calculated the total energy of the system as a function of Nb spacer layer
thickness. For each spacer layer thickness, we have done three calculations corresponding to para, ferro and antiferromagnetic
ordering of Fe atoms. The interlayer magnetic coupling is obtained from the energy difference of the systems in which Fe layers
are antiferromagnetically and ferromagnetically ordered. We find that the interlayer magnetic coupling oscillates with increasing
Nb spacer thickness in agreement with the experimental results. The induced magnetic moment is also found to be oscillating
with increasing Nb spacer layer thickness. 相似文献
14.
The interface of Fe
3
Al/Q235 dissimilar materials joint, which was made by vacuum diffusion welding, combines excellently. There are Fe
3
Al, FeAl phases and α-Fe (Al) solid solution at the interface of Fe
3
Al/Q235. Aluminum content decreases from 28% to 1.5% and corresponding phase changes from Fe
3
Al with DO
3
type body centred cubic
bcc
structure to α-Fe (Al) solid solution with B2 type
bcc
structure. All phases are present in sub-grain structure level and there is no obvious brittle phases or micro-defects such
as pores and cracks at the interface of Fe
3
Al/Q235 diffusion joint. 相似文献
15.
G. Srinivasa Gupta G. Vamsi Madhav A. Pandey B. Nageswara Sarma S. Lele 《Bulletin of Materials Science》2005,28(2):173-177
The powerful framework of cluster expansion- cluster variation methods (CE- CVM) expresses alloy free energy in terms of energy
(model) parameters, macroscopic variables (composition and temperature) and microscopic variables (correlation functions).
A simultaneous optimization of thermodynamic and phase equilibria data using CE- CVM is critically dependent on giving good
initial values of energy parameters, macroscopic and microscopic variables, respectively. No standard method for obtaining
the initial values of the energy parameters is available in literature. As a starting point, a method has been devised to
estimate the values of energy parameters from consolute point (miscibility gap maximum) data. Empirical relations among energy
parameters, temperature (T
c), composition (x
c) andd
2
T/dx2 at the consolute point, have been developed using CE- CVM free energy functions for bcc and fcc structures in the tetrahedron
and tetrahedronoctahedron approximations, respectively. Thus from the observed data ofT
c,x
c andd
2
T/dx2 in the above relations, good initial values of energy parameters can be obtained. Further, a necessary modification to the
classical NR method for solving simultaneous nonlinear/transcendental equations with a double root in one variable and a simple
root in the other has been presented. 相似文献
16.
N. Srinivasa Rao M. Purnima Shashidhar Bale K. Siva Kumar Syed Rahman 《Bulletin of Materials Science》2006,29(4):365-370
Pure and copper doped glasses with composition,x
Li
2
O-(40-x)Na
2
O-50B
2
O
3-10Bi
2
O
3,have been prepared over the range 0 ≤
x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu2+ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated.
The molecular bonding coefficients, α2 and β2, have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed
that the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows
non-linear behaviour. The IR studies show that the glassy system contains BO3 and BO4 units in the disordered manner. 相似文献
17.
P. P. Singh 《Bulletin of Materials Science》2003,26(1):131-135
Using density-functional-based methods, we have studied the fully-relaxed, fulltronic structure of the newly discovered superconductor,
MgB
2, and BeB2, NaB2 and AlB2. Our results, described in terms of (i) total density of states (DOS) and (ii) the partial DOS around the Fermi energy, EF, clearly show the importance of B p-electrons for superconductivity. For BeB2 and NaB2, our results indicate qualitative similarities but significant quantitative differences in their electronic structure due
to differences in the number of valence electrons and the lattice constantsa andc.
We have also studied Mg
1-xMxB2 (M = Al, Li or Zn) alloys using coherent-potential to describe disorder, Gaspari-Gyorffy approach to evaluate electron-phonon
coupling, and Allen-Dynes equation to calculate the superconducting transition temperature, Tc. We find that in Mg1-xMxB2 alloys (i) the way Tc changes depends on the location of the added/modified k-resolved states on the Fermi surface and (ii)
the variation of Tc as a function of concentration is dictated by the Bp DOS. 相似文献
18.
P. K. Thiruvikraman 《Bulletin of Materials Science》2006,29(4):371-374
We propose a microscopic, phenomenological model for the decrease in the viscosity observed at glass transition. Our model
is primarily applicable to chalcogenide glasses. According to this model, the decrease in the viscosity at glass transition
is mainly due to the breaking of the Van der Waals bonds in the chalcogenides. Using this model, we derive a relationship
between the glass transition temperature,T
g
,and the molar volume
V
m.The validity of this relation is checked using experimental data available in the literature for two binary systems (Ge-Se
and As-S) and a pseudo-binary system (As
40
Se
x
Te
60-x
. 相似文献
19.
A series of calcium substituted polycrystalline ferrite ceramics with magnetoplumbite structures were synthesized using perfect
stoichiometric mixtures of oxides with chemical composition, CaAlxCoxFe12−2xO19 (x = 2−5), by standard ceramic technique. The variation in the values ofH
candM
s,which depends on the additive content and the temperature, was studied by means of a vibration magnetometer. The strong variation
observed in coercivity, saturation magnetization and Curie temperature with chemical composition give rise to the possibility
of controlling these properties and hence applying these compounds in the millimeter— microwave range. 相似文献
20.
S. N. Ekbote G. K. Padam M. Sharma N. K. Arora B. S. Khurana R. C. Goel D. K. Suri N. Mehra B. K. Das 《Bulletin of Materials Science》2001,24(6):603-609
Bulk tube conductors of Bi
1.84
Pb
0.4
Sr
2
Ca
2.2
Cu
3
O
10+x
with addition of silver varying from 0 to 25 wt% (not reported earlier) were systematically studied using X-ray diffraction
(XRD), scanning electron microscopy (SEM), electrical transport and a.c. susceptibility techniques. The tube conductors formed
by cold isostatic pressing (CIP) of the powders obtained from spray drying method have been made successfully. It was found
that Ag addition has not only affected the formation of the desired Bi-2223 phase and the microstructure of these large bulk
tube samples thereby influencing on the critical current (
I
c
),it also reduces the contact resistance to minimize the cryogen losses. These variations have been found to be Ag content dependent.
An optimized value of 10 wt% Ag has been found to produce the best quality tubes showing reproducible
I
c
value > 120 Amp at 77 K which is in general a requirement to energies of the cryogen free conventional/HTSC superconducting
magnets below 20 K. 相似文献