Showing papers by "Nanjing University published in 1985"

The representation group and its application to space groups

Abstract: A so-called representation (rep) group G is introduced which is formed by all the $|\mathrm{G}|$ distinct operators (or matrices) of an abstract group \ifmmode \hat{G}\else \^{G}\fi{} in a rep space $L$ and which is an $m$-fold covering group of another abstract group g. G forms a rep of \ifmmode \hat{G}\else \^{G}\fi{}. The rep group differs from an abstract group in that its elements are not linearly independent and thus the number $n$ of its linearly independent class operators is less than its class number $N$. A systematic theory is established for the rep group based on Dirac's CSCO (complete set of commuting operators) approach in quantum mechanics. This theory also comprises the rep theory for abstract groups as a special case of $m=1$. Three kinds of CSCO, the CSCO-I, -II, and -III, are defined which are the analogies of ${J}^{2}$, (${J}^{2}$,${J}_{z}$), and (${J}^{2}$,${J}_{z}$,${\overline{J}}_{z}$), respectively, for the rotation group S${\mathrm{O}}_{3}$, where ${\overline{J}}_{z}$ is the component of angular momentum in the intrinsic frame. The primitive characters, the irreducible basis and Clebsch-Gordan coefficients, and the irreducible matrices of the rep group G in any subgroup symmetry adaptation can be found by solving the eigenequations of the CSCO-I, -II, and -III of G, respectively, in appropriate vector spaces. It is shown that the rep group G has only $n$ instead of $N$ inequivalent irreducible representations (irreps), which are just the allowable irreps of the abstract group \ifmmode \hat{G}\else \^{G}\fi{} in the space $L$. Therefore, the construction of the irreps of \ifmmode \hat{G}\else \^{G}\fi{} in $L$ can be replaced by that of G. The labor involved in the construction of the irreps of the rep group G with order $|\mathrm{G}|$ is no more than that for the group g with order $|\mathrm{g}|=\frac{|\mathrm{G}|}{m}$, and thus tremendous labor can be saved by working with the rep group G instead of the abstract group \ifmmode \hat{G}\else \^{G}\fi{}. Based on the rep-group theory, a new approach to the space-group rep theory is proposed, which is distinguished by its simplicity and applicability. Corresponding to each little group G(k), there is a rep group ${\mathbf{G}\ensuremath{'}}_{\mathrm{k}}$. The $n$ inequivalent irreps of ${\mathbf{G}\ensuremath{'}}_{\mathrm{k}}$ are essentially just the acceptable irreps of the little group G(k). Consequently the construction of the irreps of G(k) is almost as easy as that of the little co-group ${\mathbf{G}}_{0}$(k). An easily programmable algorithm is established for computing the Clebsch-Gordan series and Clebsch-Gordan coefficients of a space group simultaneously.

Radiation effects on polyethylene and polypropylene by electrons and protons

Abstract: The irradiation of low-density polyethylene and polypropylene films has been carried out by using 20-keV proton and 8-MeV electron beams. Measurement of mechanical properties and X-ray diffraction have shown that the tensile strength and elongation of electron-irradiated polyethylene have improved as a function of electron dose, suggesting the occurrence of cross-linking with proper irradiation dosage. On the contrary, rapid degradation of electron-irradiated polypropylene has been noticed. Protons have quite different effects on these two polymers: they caused a small decrease in the mechanical properties of polyethylene on the one hand, and on the other the mechanical properties of polypropylene were greatly improved (increase in its tensile strength σ ( kg cm 2 ) by 51% and that of its elongation ϵt by 36%. This effect may be attributed to the collision of the incident proton beam with protons in the polypropylene chains, forming cross-links between macromolecules of propylene. This is probably the first time that the cross-linking of polypropylene by proton bombardment has ever been observed.

A TEM study of the incommensurate phase and related phase transitions in barium sodium niobate

Abstract: Experimental results are given on the incommensurate phase and on related phasetransitions in barium sodium niobate obtained by means of electron diffraction and electron microscopy. Evidence is found for discommensurations (DC) in the quasicommensurate phase of barium sodium niobate with detailed observations. A crystallographic model for the commensurate phase and for discommensurations in barium sodium niobate compatible with the observations is deduced. In this model the space group for the commensurate phase is Bbm2, and the discommensurations are antiphase boundaries with translation vectors [100]tetra or [010]tetra. In-situ observations during a change of temperature show that the multiplication and the nucleation of DCs occur near 280 °C, and the incommensurability parameter δ changes abruptly by one order of magnitude, this corresponds to the commensurate to incommensurate phase transition. Electron diffraction patterns show that incommensurate satellite diffraction spots persist in the tetragonal phase of barium sodium niobate and only disappear at about 600 °C near the ferroelectric–para-electric phase transition point. Mittels Elektronenmikroskopie und Elektronenbeugung werden die inkommensurable Phase und damit verknupfte Phasenubergange in Barium-Natrium-niobat untersucht. Es werden Hinweise fur Diskommensurationen (DC) in der quasikommensurablen Phase von Barium–Natriumniobat durch ausfuhrliche Beobachtungen gefunden. Ein kristallographisches Modell der kommensurablen Phase und fur die Diskommensurationen in Barium-Natrium-niobat, das mit den Beobachtungen kompatibel ist, wird abgeleitet. In diesem Modell ist die Raumgruppe fur die kommensurable Phase Bbm2, und die Diskommensurationen sind Antiphasengrenzen mit Translationsvektoren [100]tetra oder [010]tetra. In-situ-Beobachtungen wahrend der Temperaturanderung zeigen, das die Multiplikation und die Keimbildung der DC bei etwa 280 °C auftreten, und der Inkommensurabilitatsparameter δ sich um eine Grosenordnung andert, dies entspricht dem Phasenubergang: kommensurabel nach inkommensurabel. Elektronenbeugungsdiagramme zeigen, das inkommensurable Satellitenbeugungspunkte in der tetragonalen Phase von Barium-Natrium-niobat zuruckbleiben und nur verschwinden oberhalb 600 °C in der Nahe des Phazenubergangspunktes ferro-elektrisch–paraelektrisch.

Orientation studies of poly(ethylene terephthalate) film and fiber surfaces using FT‐IR diffuse reflectance optics

Abstract: Etude d'echantillons orientes ou non pour determiner la sensibilite de la technique vis-a-vis de l'influence de l'orientation moleculaire

Untuned low insertion loss surface leaky wave filter

Abstract: The letter presents a broadband low insertion loss surface leaky wave filter using reflective multistrip couplers on an optimum cut and orientation of lithium niobate. The insertion loss has been reduced to 3-4 dB without any inductors for phase-shift networks or tuning, and the out-of-band rejection is about 23 dB. The fractional bandwidth is up to 2-5%. The out-of-band rejection can be reduced to 40 dB, when the IDTs are apodised.

The influences of orography upon the flow within Ekman boundary layer under the approximation of geostrophic momentum

Abstract: In this paper, the influences of orography on the boundary layer flow with the approximation of geostrophic momentum are studied. The wind velocity at the lower boundary will not always be zero when the orography exists. So the structure of the boundary layer flow, as well as the vertical velocity at the top of the boundary layer, is affected. There are three factors affecting the vertical motion at the top of the boundary layer: lifting due to orography; divergence due to Ekman flow, and advection of the geostrophic momentum. These effects and the features of the flow within the boundary layer are discussed in detail.

Studies on the analgesic effects of lanthanides

Abstract: The analgesic effects of ten lanthanides have been examined. The intraventricularly administered lanthanides produced a long-lasting analgesia. These effects were antagonized by divalent cations. Yttrium had no analgesic effect and was unaffected by the divalent cations, indicating that the analgesia is possibly a mutual characteristic of the lanthanide series of elements, but not of the rare earths. Naloxone fully or partly reverses the analgesic effects of the lanthanides, morphine or electroacupuncture, and at the same time increases the Ca 2+ levels in the brain. Naloxone, however, has no effect on the EGTA-induced analgesia and the Ca 2+ levels in the brain. All these findings indicate that the lanthanides are likely to share a mutual antinociceptive site and analgesic mechanism with those of morphine and electroacupuncture.

Content of magnetic monopoles in quasars, galactic nuclei and stars and their astrophysical effects

Abstract: Estimations of the number of monopoles preserved and captured in the formation process of quasars, galactic nuclei and stars have been presented here. (ⅰ) The monopoles in quasars and other galactic nuclei are preserved in their formation process. And monopole content, ξ≡N_m/N_B, may be higher than the Newton saturation value, i. e. ξ≥ξN((?)2×10~(25)). (ⅱ) The monopoles in normal stars (including the sun), planets (e. g. the earth) and compact stars (white dwarfs and neutron stars) are mainly captive. For normal stars and planets ξ《ξN; for white dwarfs and neutron stars either ξ《ξN if the cross section of the Rubakov-Callan effect is much larger than 10~(-2), σβ/10~(-27)》10~(-2), or ξ﹋∽～ξN if not. (ⅲ) The monopoles in the center of the objects produce a radially magnetic field. The detection of the field may give limitations to the cross section of the RC effect.

Applications of the extrapolation method to the numerical solution of singular perturbation problems

Abstract: In this paper we consider applications of extrapolation method to the numerical solution of singular perturbation problem for elliptic—parabolic equation in order to manifesting accuracy of approximations and estimate the order of accuracy. Concerning the uniform convergence in ref. [1], its proof is given in the appendix.

CALCULATION OF MAGNETOCRYSTALLINE ANISOTROPY OF Nd 2 Fe 14 B

Abstract: The contribution of Nd3+ ions to the magnetocrystalline anisotropy of intermetallic compound Nd2Fe14B was calculated by single ion theory. The results explained the high anisotropy of Nd-Fe-B alloy. By adjusting the shielding factors the calculated K1-T and K2-T relations agree with the experimental curves.

Dynamical Theory of Classical Surface Plasmas II

Abstract: The first and second equations of the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy have been solved for the electron gas. Adopting a procedure parallel to Coste calculation for situation, the authors obtain a new expression for the dynamical polarizability valid over the entire range of . In the long wavelength limit, the dynamical superposition structure emerges as remarkable and clusters. Low frequency response is formulated. Both the collisional and correlational corrections have been, explicitly calculated. We also discuss the structure of the low frequency excitation modes and ultimately determine the collisional contribution and the leading term of the correlational contribution to the damping.

Solar modulation of cosmic ray intensity and solar flare events inferred from (14)C contents in dated tree rings

Abstract: The delta 14C values in 42 rings of a white spruce grown in Mackenzie Delta was measured as a continuing effort of tracing the history of solar modulation of cosmic ray intensity. The delta 14C values in six rings were measured, in search of a 14C increase due to two large solar flares that occurred in 1942. The results are presented.

The influence of horizontally non-uniform heating upon the development of strong convective mesoscale disturbances

Abstract: It is shown by observational data and synoptic analysis that the development of strong convective echo is influenced by the horizontally non-uniform heating, such as the one caused by lake-land distribution. In this paper, a simple linear cell-convection model is established using an appropriate heating field, and the instability of heating convection is theoretically studied. It is found that the heating convection development will be unstable if the heating-caused temperature gradientdT0/dy is greater than the critical value (dT0/dy)c which is approximately 0.64°C/10 km, and that the development of convective band has a preferred width of 12.5 km. It will take 25 min for the initial disturbance to increase intensity by 10 times. All these results are in rather good agreement with the squall line process in the lake-land region of Jiangsu Province on June 8, 1979.

Laser Recrystallization of Mocvd Poly-Gaas on Insulating Substrates

Abstract: Poly-GaAs films have been grown on amorphous insulating substrates by MOCVD technique. The films were analyzed using TEM, X-ray diffraction, AES and ESCA measurements. The results show that poly-GaAs films are flat, bright and close in texture and stoichiometric. The grain size is about 200A. The film contains trace impurities such as Si,0 and C. They are evenly distributed in the film. The poly-GaAs films were crystallized by CW % MathType!MTEF!2!1!+- % feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeyqamaaxa % cabaGaaeOCaaWcbeqaaiabgUcaRaaaaaa!38DB! ${\text{A}}\mathop {\text{r}}\limits^ + $ laser with a increase of grain size from 200A to 40 µm. Schottky barrier diodes of good I–V characteristics were made on the laser recrystallized GaAs films.

Distorted kossel diffraction of LiNbO 3 in the vicinity of 75°C

Abstract: Some abnormal Kossel lines of pure LiNbO3 crystal have been observed in the vicinity of 75°C and in Ti-diffused one at wide temperature range. Reasonable explanation is that the diffraction plane inclines locally from its normal position at that temperature. A computer simulation has been made and shows an agreement with the calculations. The change of elastic constant or heat expansion coefficient etc. may be the cause of the deformation of the pure crystal near 75°C.

Studies on thermal stabilities of coordination compounds by gas chromatography: IX. Thermal decomposition of Fe2(C2O4)3‐HZSM‐5 and Fe2(C2O4)3‐HY

Abstract: Some properties and thermal decomposition of iron (III) oxalate supported on HZSM-5 and HY zeolites have been studied by GC, IR, and Mossbauer spectroscopy methods. Thermal decomposition of unsupported iron (III) oxalate took place in two stages: as indicated by peak α (giving CO2) and peak γ (yielding CO and CO2), but for iron (III) oxalate supported on zeolites, an additional peak β (producing CO and CO2) appeared as a result of the interaction between C2O42− and Al3+. At 500°C Fe2(C2O4)3-HZSM-5 system produced α-Fe in H2 due to the weak interaction between the salt and the support. For Fe2(C2O4)3-HY system in H2, at 500° the solid products consisted of α-Fe and a little highly dispersed Fe (0) together with Fe (II) and F(III) oxides, which were difficult to be reduced.