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1.
Abstract This paper proposes a simple method for deriving the geometric stiffness matrix (GSM) of a three‐node triangular plate element (TPE). It is found that when the GSM of the element is combined into the global one of the structure, this structural stiffness matrix becomes symmetric and satisfies both the rigid body rule and incremental force and moment equilibrium (IFE) conditions, which are basically two fundamental conditions for analysis of mechanics. The former condition has been widely used in the community of mechanics; while the latter one, to our best knowledge, has never been considered. Advantages with the GSM derived are that derivations only need simple matrix operations without cumbersome non‐linear virtual strain energy derivations and tedious numerical integrations and more appealingly, this derived GSM can be explicitly given for applications. In addition, based on IFE and the rigid body rule conditions, a reasonable GSM for the three‐node TPE must be asymmetric; however, an asymmetric matrix usually gives rise to tedious numerical calculation especially in geometrically nonlinear problems and further, greatly influences computation efficiency. Fortunately, the skew‐symmetric parts of the derived GSM can be canceled out once they are merged into the global stiffness matrix of the structure. In this regard, this structural stiffness matrix becomes a symmetric one and thus enhances its effectiveness. Finally, several examples are provided for validating the robustness of the derived GSM. 相似文献
2.
AbstractBased on the characteristics of the laser device and the inevitable error of the processing technique, a laser beam emitted from a communication terminal can be represented by the Gaussian Schell model (GSM). In space-to-ground link laser communications, the optical intensity is affected by the source coherence parameter and the zenith angle. With full consideration of these two parameters, the statistical distribution model of the optical intensity with a GSM laser in both downlink and uplink is derived. The simulation results indicate that increasing the source coherence parameter has an effect on the statistical distribution of the optical intensity; this effect is highly similar to the effect of a larger zenith angle. The optical intensity invariably degrades with increasing source coherence parameter or zenith angle. The results of this work can promote the improvement of the redundancy design of a laser communication receiver system. 相似文献
3.
Abstract The generation of a partially coherent laser beam directly from a spatial-temporal phase modulated optical resonator is investigated both experimentally and theoretically. The laser material used in the experiment is Nd:YAG rod pumped by Krypton lamps working in continuous wave mode. The phase modulation is fulfilled by an intra-cavity LiNbO3 electro-optic crystal driven by high voltage. The experimental results show that intracavity phase modulation is an effective way to generate partially coherent laser beams. The theoretical analysis and numerical simulation shows that the output beam can be characterized by Gaussian Schell-model (GSM) beams. The two-slit interference experiment confirms that the output beam is partially coherent. 相似文献
4.
Leilei Pan 《Journal of Modern Optics》2013,60(21):2340-2347
According to the extended Huygens–Fresnel integral, the expressions for the on-axis spectrum of partially coherent Gaussian Schell-model (GSM) rectangular array beams passing through ABCD optical systems have been derived. The generalized Fresnel number of the system, the spatial coherent parameter of array beamlets and the array beam parameters including the number of beamlets and the separation distance between beamlets have been taken as the characteristic parameters to compare the spectral shifts of GSM array beams for the two types of the superposition, i.e. the correlated superposition and the uncorrelated superposition. In particular, the effect of characteristic parameters on the on-axis relative spectral shifts has been discussed in detail. The results show that the spectral intensity of GSM array beams for the two types of the superposition passing through ABCD systems depends on the source spectral density S 0(ω), the spatial coherent parameter of array beamlets β, the generalized Fresnel number of the system F and the array beam parameters. Furthermore, for the uncorrelated superposition, the spectrum of GSM array beams only exhibit the blue-shift, whereas for the correlated superposition, GSM array beams exhibit the spectral switch and the number of spectral switches increases with the increase of array beam parameters in the near field due to the interference between beamlets. In particular, the effect of the array beam parameters on the on-axis relative spectral shift is more obvious. 相似文献
5.
In November 2012 the Google Scholar Metrics (GSM) journal rankings were updated, making it possible to compare bibliometric indicators in the ten languages indexed—and their stability—with the April 2012 version. The h-index and h-5 median of 1,000 journals were analysed, comparing their averages, maximum and minimum values and the correlation coefficient within rankings. The bibliometric figures grew significantly. In just seven and a half months the h-index of the journals increased by 15 % and the median h-index by 17 %. This growth was observed for all the bibliometric indicators analysed and for practically every journal. However, we found significant differences in growth rates depending on the language in which the journal is published. Moreover, the journal rankings seem to be stable between April and November, reinforcing the credibility of the data held by Google Scholar and the reliability of the GSM journal rankings, despite the uncontrolled growth of Google Scholar. Based on the findings of this study we suggest, firstly, that Google should upgrade its rankings at least semi-annually and, secondly, that the results should be displayed in each ranking proportionally to the number of journals indexed by language. 相似文献
6.
Pan L Yuan X Ding C Lü B 《Journal of the Optical Society of America. A, Optics, image science, and vision》2008,25(8):2122-2128
Taking the Gaussian Schell-model (GSM) beam as a typical example of partially coherent beams, the analytical expressions of the spectrum of GSM beams propagating in dispersive media are derived, and the spectral properties are studied in detail. It is shown that, in comparison with propagation in free space and in turbulence, whether or not GSM beams satisfy the scaling law, the normalized spectrum of GSM beams in dispersive media changes on propagation in general, because the dispersive medium affects different spectral components differently. As compared with the free-space propagation, for the scaling-law GSM beams the dispersion results in spectrum change, and for the nonscaling-law GSM beams the dispersion gives rise to a further increase in spectral changes. The structure constant of the dispersive property of the media, the transverse coordinate of the observation point, the spatial correlation length of the source, and the propagation distance affect the spectral behavior of GSM beams; this effect is illustrated numerically. 相似文献
7.
Synthesis of Hg(Tl)Ba
2
Ca
2
Cu
3
O
8+δ
superconducting tapes have been accomplished by annealing the precursor tape, Ba
2
Ca
2
Cu
3
O
y
(fabricated by doctor blade tape casting technique) in an environment of Hg(Tl) vapour. Characterization of superconducting
HTSC tape sample was carried out through XRD, TEM, SEM and R-T measurements. Surface morphological investigations of the as-synthesized
Hg(Tl)Ba
2
Ca
2
Cu
3
O
8+δ
HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like
features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small
crystal like grains of superconducting material Hg(Tl)Ba
2
Ca
2
Cu
2
O
8+δ
.The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence
of growth fronts formed from Hg(Tl):1223 and Hg(Tl):1234 nuclei. 相似文献
8.
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
9.
A. Venkataraman Vijay A. Hiremath S. K. Date S. D. Kulkarni 《Bulletin of Materials Science》2001,24(6):617-621
A new combustion route for the synthesis of γ-Fe
2
O
3
is reported by employing purified a-Fe
2
O
3
as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves
fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the
reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe
2
O
3
.The as synthesized γ-Fe
2
O
3
is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on
magnetic properties is also presented. 相似文献
10.
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
11.
Silicate based bioceramics are promising candidates as biomaterials for tissue engineering. The combustion synthesis method
provides control on the morphology and particle size of the synthesised material. This paper discusses the combustion synthesis
of akermanite (Ca
2
MgSi
2
O
7
and Sr
2
MgSi
2
O
7
), which has been shown to have good in vitro and in vivo bioactivities by earlier studies. Both Ca
2
MgSi
2
O
7
and Sr
2
MgSi
2
O
7
have akermanite structure. Ca
2
MgSi
2
O
7
and Sr
2
MgSi
2
O
7
were prepared using urea and ammonium nitrate. The combustion synthesis using urea and ammonium nitrate was found to be cost
effective and efficient method of synthesis. The photoluminescence study of Ca
2
MgSi
2
O
7
: Eu2+^{\boldsymbol{2+}} and Sr
2
MgSi
2
O
7
: Eu2+^{\boldsymbol{2+}} shows host specific intense emission of Eu2+^{\boldsymbol{2+}}. 相似文献
12.
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
13.
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
14.
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
15.
Tantalum oxide (Ta
2
O
5
) films and Al/Ta
2
O
5
/Si MOS capacitors were prepared at various powers by ultraviolet photo-inducing hot filament chemical vapour deposition (HFCVD).
Effects of ultraviolet light powers on the structure and electrical properties of Ta
2
O
5
thin films were studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The dielectric constant, leakage
current density and breakdown electric field of the samples were studied by the capacitance–voltage (C–V) and current–voltage
(I–V) measurements of the Al/Ta
2
O
5
/Si MOS capacitors. Results show that the Ta
2
O
5
thin films grown without inducement of UV light belong to amorphous phase, whereas the samples grown with inducement of UV-light
belong to δ-Ta
2
O
5
phase. The dielectric constant and leakage current density of the Ta
2
O
5
thin films increase with increasing powers of the UV- lamps. Effects of UV- lamp powers on the structural and electrical
properties were discussed. 相似文献
16.
Chunguang Shao Zhe Ma Ranran Zhuo Ruijing Zhang Changyu Shen 《Journal of Materials Science》2012,47(7):3334-3343
Structure changes of syndiotactic polypropylene (sPP) under uniaxial stretching are studied with the combination of micro-tensile
tester and in situ wide angle X-ray diffraction (WAXD) measurement. Lamellae stacked “vertically” and “parallel” to the stretching
direction (defined as “V” and “P” part) are separated on the basis of two-dimensional WAXD patterns. For all samples with
different lamellar thickness, two critical points named as b
1
and b
2
were found in the stress–strain curves, while b
1
and b
2
points are the onsets of the rotation for the lamellae of “V” part and “P” part, respectively. The corresponding true stress
and true strain for b
2
point are bigger than that of b
1
, demonstrating that for samples with initial isotropic lamellar orientation, inhomogeneous deformation of crystalline skeleton
induced by uniaxial stretching is universal. And after b
1
point, “stress-induced melting” always occurs simultaneously with lamellar slips. Furthermore, the relationship between lamellar
thickness and the true stress for b
1
and b
2
point was also studied, illustrating a linear correlation between ln σ and 1/l (σ is the corresponding true stress, l is the lamellar thickness), consistent with Young’s model. However, the critical true strains for these two points did not
change with the varying thickness. 相似文献
17.
The enthalpies of solution of anhydrous and hydrated uranyl benzenesulfonate (I) and p-toluenesulfonate II) in 4 M HCl were determined. The standard enthalpies of formation of I and II and their crystal hydrates from uranium trioxide, sulfonic acids, and water and enthalpies of water addition to anhydrous salts and lower hydrates of II were calculated. The enthalpy of addition of water molecule to II·H2O is about half that of addition to II·3H2O. With regard to all approximations in calculations, the enthalpy of formation of II from amorphous uranium trioxide and aqueous solution of the corresponding acid is by approximately 20 kJ mol-
1 more negative as compared to I. It was concluded that the electron-donor power of the p-toluenesulfonate ion is noticeably greater than that of the benzenesulfonate ion, which determines the difference in the properties of II and I. 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.
Ca
4
Mg
5
(PO
4
)
6
:Eu2+^{\boldsymbol{2+}} blue-emitting phosphor was synthesized by the combustion-assisted synthesis method under reductive atmosphere. The products
were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectrum.
XRD analysis confirmed the formation of Ca
4
Mg
5
(PO
4
)
6
pure phase. Photoluminescence results showed that the phosphor can be excited efficiently by UV light range from 230–400 nm,
and then exhibited bright blue light with peak wavelength at 431 nm. It is a very promising candidate as a blue-emitting phosphor
for potential applications in display devices. 相似文献
20.
Zheng Wang Feng Tao Long-yi Xi Kai-ge Meng Wei Zhang Ying Li Qing Jiang 《Journal of Materials Science》2011,46(11):4005-4012
Two novel conjugated copolymers consisting of alternating electron-rich propylenedioxythiophene and electron-deficient 2,3-diphenyltheno[3,4-b]pyrazine
or 6,7-diphenyl[1,2,5]thiadiazole units have been synthesized through palladium catalyzed Sonogashira triple-bond coupling
reaction. The structures and properties of the two copolymers, P
1
, P
2
, were characterized by FT-IR, NMR, UV–Vis absorbance (Abs), thermal gravimetric analysis (TGA), differential scanning calorimetry
(DSC), and cyclic voltammetry (CV). UV–Vis absorption spectra of the polymers show two absorption bands both in CHCl3 solution and films. The absorption peak maxima of P
1
, P
2
are 600 nm, 766 nm in solution and 627 nm, 823 nm in films, respectively. Thermal gravimetric analysis demonstrates that
the two polymers are stable below 300 °C. Cyclic voltammetry studies reveal that the band gaps of P
1
, P
2
are 1.62 eV and 1.50 eV, suggesting their potential for applications as organic solar cell materials. 相似文献