Showing papers by "Nanjing University published in 1988"

Pulsars, X-ray synchrotron nebulae, and guest stars

Abstract: X-ray observations of supernova remnants and radio pulsars are used to derive luminosities of neutron stars and synchrotron nebulae Observations of known isolated pulsars are used to develop an empirical relationship between the X-ray luminosity and the rate of loss of rotational energy This is used to derive the characteristics of pulsars hidden in remnants which show evidence for a central compact object or associated nebular emission, but no clear pulsed signal from the neutron star itself Possible periods and period derivatives for the hidden pulsars are discussed Some might have periods as long as 05 s, and period derivatives considerably higher than that of PSR 1509 - 58, currently the pulsar with the highest known period derivative

TEM study of phases and domains in NaNbO3 at room temperature

Abstract: It is found with TEM that there is a new phase, called M phase, coexisting with the normal P and Q phases at room temperature. All kinds of ferroelectric domains in the Q phase and antiferroelectric domains in the P phase are observed. They are in good agreement with the results given by the symmetry theory on domains and domain wall orientations in the ordered phase. Translation domain walls (TDWs) are also observed in the P phase as well as in the Q phase. The translation vector was determined as [100]p (here p means pseudocubic unit cell). In addition, the effect of translation domain walls on electron diffraction is reported and interpreted theoretically. It is concluded that NaNbO3 (NN) is a heterogeneus system both in phases and in domains at room temperature. Mit Hilfe der Transmissionselektronenmikroskopie wird eine neue Phase (M-Phase) gefunden, die mit den normalen P- und Q-Phasen bei Raumtemperatur zusammen existiert. Es werden alle Arten ferroelektrischer Domanen in der Q-Phase und antiferroelektrischer Domanen in der P-Phase beobachtet. Sie befinden sich in guter Ubereinstimmung mit den Ergebnissen der Symmetrietheorie fur Domane und Domanenwandorientierungen in der geordneten Phase. Translationsdomanenwande werden sowohl in der P-Phase ais auch in der Q-Phase beobachtet. Der Translationsvektor wird zu [100]p (p bezeichnet die pseudokubische Einheitszelle) gefunden. Auserdem wird ein Einflus von Translationsdomanenwande auf die Elektronenbeugung beobachtet und theoretisch interpretiert. Es wird gefolgert, das NaNbO3 (NN) ein heterogenes System sowohl bezuglich der Phasen als auch der Domancn bei Raumtemperatur darstellt.

Effect of structural instability between 80 and 300 K on superconductivity of YBa2Cu

Abstract: The lattice parameters of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{x}}$ have been carefully measured by x-ray polycrystalline diffraction between 80 and 300 K. As a function of temperature, they reveal a large variation above ${T}_{c}$, which is mainly attributed to a few abrupt changes near certain temperatures rather than thermal expansion. Such structure instability, accompanied with the appearance of internal friction peaks and elastic softening, is related to oxygen content x. The instability near 120 K was found to be related to the superconductivity at 90 K.

Evidence of alpha correlation from binding energies in medium and heavy nuclei.

Abstract: If the effect of \ensuremath{\alpha} clustering due to the interaction of the excited correlated proton pair with correlated neutron pairs in medium and heavy nuclei were taken into consideration, quasiparticle energies would not be simply additive. The empirical values of the extra term \ensuremath{\delta}(\ensuremath{\alpha}) indicate that \ensuremath{\alpha} correlations exist to a certain extent in these nuclei.

Internal friction transitory effects associated with martensitic transformation in NiTi alloys

Abstract: Low-frequency (≈ 1 Hz) internal friction associated with the martensitic transformation in NiTi, is systematically investigated under diverse heating and cooling rates T. The main contribution to the internal friction is due to transistory phenomena which decrease to zero with T. It is shown that the transitory internal friction does not depend linearly on the T heating or cooling rate, as it was predicted by the classical theories. Le frottement interieur basse frequence (≈ 1 Hz) associe a la transformation martensitique du NiTi a ete mesure systetiquement sous diverses vitesses de chauffage ou de refroidissement T. La plus grande contribution au frottement interieur est due a des phenomenes transitories qui s'annulent lorsque la vitesse T tend vers zero. On montre que le frottement interieur transitorie n'cst pas une fonction lineire de la vitesse T comme cela etait predit par la theorie classique.

In situ TEM studies of para—ferro phase transitions in NaNbO3

Abstract: It is found from TEM observations in NaNbO3 crystals that the phase transition series from the P phase is P—R1—R2—S and that one, related to the Q phase is Q—Q1—Q2—S. It is shown that the R phase is composed of two subphases R1 and R2. The main difference between R1 and R2 is that the η values corresponding to these two phases in the superlattice spots [1/2, 1/2 ± η1/2, 0]* are 1/4 and 1/6, respectively. But the η values in the superlattice spots [1/2 ± η 1/2, 0]* corresponding to the Q1 and Q2 phases are 0 and 1/3, respectively. The main soft mode of the transition from phase S to R2 is determined as the zone boundary transverse optical mode Σ2 with wave vector q equal to [1/2, ξ, 0]*. The appearance of a superlattice spot at [1/2, 1/2, 0]* shows that the mode characterizing the tilt of octahedra is also softened due to mode—mode coupling. Aus TEM-Beobachtungen in NaNbO3-Kristallen wird gefunden, das die Phasenubergangsserien von der P-Phase P—R1—R2—S sind und das Q—Q1—Q2—S mit der Q-Phase verknupft ist. Es wird gezeigt, das die R-Phase aus zwei Subphasen R1 und R2 zusammengesetzt ist. Die Hauptdifferenz zwischen R1 und R2 ist, das die η-Werte entsprechend diesen beiden Phasen in den Supergitterreflexen [1/2, 1/2 ± η, 0]* 1/4 bzw. 1/6 betragen. Jedoch sind die η-Werte in den Supergitterreflexen [1/2 ± η, 1/2, 0]* entsprechend der Q1- und Q2-Phase 0 bzw. 1/3. Die Haupt-Softmode des Ubergangs von Phase S zu R2 wird als transversale optische Zonengrenzenmode ∑2 mit Wellenvektor q gleich [1/2, ξ, 0]* bestimmt. Das Auftreten eines Supergitterreflexes bei [1/2, 1/2, 0]* zeigt, das die Mode, die die Oktaederkippung charakterisiert, infolge Moden—Moden-Kopplung erreicht wird.

Systems programming in the functional language FP

Abstract: The development of systems software in functional programming language is still an open problem. This paper describes a preliminary experiment with systems programming in Backus’ FP systems[1]. It consists of two systems programs. One is a self-compiler of FP, the other an interpreter of the semantics of FFP (Formal Functional Programming). Both were implemented on an FP machine—FPM2. Some discussions are made finally.

Time-Space Distribution of Tin/Tungsten Deposits in South China and Controlling Factors of Mineralization

Abstract: The abundant tin and tungsten deposits in South China were formed in different geologic ages. They began to appear in the late Protereozoic, and reached their paramount development during the Yenshanian period. In regional distribution the W deposits tend to occur in the eastern part of this region, mostly in post-Caledonian uplifts, while the Sn deposits tend to occur in the western part, mostly in Hercynian-Indosinian depressions. Both of them are found either within the middle-late Pro-terozoic and lower Paleozoic basemental structure, or adjacent to the basement rocks. Genetically, they are mainly associated with continental crustal anatectic granitoids. The following factors are considered to be most important in controlling the time-space distribution of Sn/W deposits: regional existence of ore source beds of middle-late Proterozoic and early Paleozoic ages; crustal mechanism in the generation of multi-cyclic granitoids and their evolution; activities of ore-bearing hydrothermal solutions; and localization of Sn/W mineralization in close relation to structural environment and wall rock properties.

Dynamical Evolution of the Rotation of Venus

Abstract: By considering the torque of the bodily tides, the effect of the core-mantle viscous coupling and the torque of the atmospheric tides have been obtained by numerical calculation: the evolution of the spin angular velocity Ω♀ and the obliquity β of the Venus are calculated numerically with the step-variable Runge-Kutta method of 7th order; and 7 sets of the probable Cytherean spin evolution have been obtained. It is indicated that the present spin state of Venus is the result of long-term evolution within the reasonable ranges of some disposable parameters. The early spin period is between 7 h to 2 d and the corresponding obliquity is about 90 ° ~ 100 °. The effects of the torques of body and atmospheric tides and the core-mantle viscous coupling of Venus on its spin angular velocity could nearly cancel out each other about a billion years ago. Therefore, Venus could have been captured in a spin-orbit resonant state by the gravitational torque of the Earth on the permanent deformation part of Venus; and this resonant state has lasted up to the present time.

A study of tolypocladium sinense c.l.li.sp.nov and cyclosporin production

Abstract: Fresh Contaminate specimens of Cordyceps sinensis (Berk.) Sacc.col- lected from Diqing Tibeten Austonompus Prefecture,Yunnan province,the contamina- tion were isolated and cultivated to obtain a pure species.It was identified as a new species of Tolypocladium namely Tolypocladlum sinanse C.L.Li.sp.nov.It forms phialides and phialospores in several agar media,the base of phialides are spherical or elliptical and terminated by slender,curved neck bearing globose to ovoid phialos- pores.The morphological characteristics of the new species are given in comparison with other species of Tolypocladium,it is obviously different from other species of Tolypocladium in shape and size of phialospores as well as phialides,also hosts and habitats,therefore we consider Tolypocladium sinense as a new species The new species is cultivated by submerged culture in liquid medium composed of peptone,glucose,inorganic salt etc,at 26℃,pH5.2,on shakers for 12days.The fermentation broth was extracted with an equal volume of acetic ether and the orga niclayer was separated and evaporated under reduced pressure.In this way 1 liter of fermentation broth yield approximately 50—80 mg of crude materal of cyclosporin. The crude materal exhibit antifungal activity for strains of some imperfect fungi.

The influence of radiation pressure on equipotential surfaces in high-temperature binary systems

Abstract: In this paper we considered the effect of the radiation pressure from both components of the high-temperature binary systems in terms of a modified Roche potential. Usually, the parameters of radiation pressures δ1, δ2 can be written as a function of radiiR, effective temperatureT eff , and massM of components. The simulation calculation shows that the positions of saddle pointsL 1 ,L 2 ,L 3 and shape of critical surface are changed with radiation pressure factors δ1, δ2. Consequently, use of the conventional critical Roche model to estimate value of radii and mass ratios may be completely unwarranted if effective temperature of both componentsT eff ≥30 000 K. These conclusions are applied to Wolf-Rayet binary systems V444 Cygni,v 2 Velorum, and O-type binary system Y Cygni. The modified critical potentials are calculated and discussed.

A study of ferroelectric domain patterns in orthorhobic KNbO3 with optical microscopy

Abstract: Ferroelectiric domain patterns in natural surface layers of Czochralski as-grown crystals are very complicated. The inner domain patterns are comparatively simple and consist of a regular arrays of so-called thin lens-like 90° domains. Only few inner 60° and 120° domains crossing the 90° domain arrays are observed. The inversion or 180° domains are shape-like separated islands. The 60° microdomains are easily introduced into the surface layers during the specimen processing. There are some elastic interactions between the different kinds of ferroelectric domain walls, the orientations of which are in good coincidence with the theory proposed by Janovec.

Direct observation of α-β phase transition in KNbW2O9 by transmission electron microscopy

Abstract: KNbW2O9 crystal with the hexagonal tungsten bronze structure is studied by TEM and electron diffraction. It is shown that KNbW2O9 has a well-marked superstructure with tripling and doubling of unit cell dimensions along a and c, respectively. A kind of “extended antiphase boundaries” with certain width is observed in the crystals below the β α phase transition temperature (T < 570 °C). The structure of these boundary layers may be similar to or equivalent to the structure of the high temperature α phase. These act as prefabricated nuclei for the α phase. The β α phase transition proceeds simply by the extending of these boundary layers. There is a coexistence of the α and β phase; the phase transition is of first order. Ein KNbW2O9-Kristall mit hexagonaler Wolframbronzestruktur wird mittels TEM und Elektronenbeugung untersucht. Es wird gezeigt, das KNbW2O9 eine gut ausgepragte Superstruktur besitzt, mit Verdreifachung und Verdopplung der Ausdehnungen der Einheitszelle in Richtung a bzw. c. Eine Art von “ausgedehnten Antiphasengrenzen” mit bestimmter Breite wird in den Kristallen unterhalb der β α-Phasenubergangstemperatur (T < 570 °C) beobachtet. Die Struktur dieser Grenzschichten kann ahnlich oder aquivalent zur Struktur der Hochtemperatur-α-Phase sein. Diese wirkt als vorgefertigter Keim fur die α-Phase. Der β α-Phasenubergang vollzieht sich einfach durch Ausdehnung dieser Grenzschichten. Es gibt eine Koexistenz der α- und β-Phase; der Phasenubergang ist von erster Ordnung.

Lattice expansion and phonon softening in Nb/Cu superlattices

Abstract: Nb/Cu superlattices with modulation wavelength in the range 1 to 30 nm are synthesized by magnetron sputtering. Both, X-ray diffraction and ion mill Auger electron spectroscopy techniques are used to determine the structure of the superlattices. The X-ray experiments reveal two anomalous expansions in the average lattice spacing at modulation wavelengths λ = 2 and 8 nm. Ultrasonic measurements of the surface-acoustic-wave (SAW) velocities in the superlattices show that surface phonons soften at the same two modulation wavelengths. A preliminary explanation of the experimental results is presented. Nb/Cu-Supergitter mit Modulationswellenfangen im Bereich 1 bis 30 nm werden mittels Magnetronsputtering synthetisiert. Sowohl Rontgenbeugung als auch Ionenzerstaubungs-Augerelektronenspektroskopie werden benutzt, um die Struktur der Supergitter zu bestimmen. Die Rontgenexperimente zeigen zwei anomale Expansionen im mittleren Gitterabstand bei Modulationswellenlangen λ = 2 und 8 nm. Die Ultraschallmessungen der Geschwindigkeiten der akustischen Oberflachenwellen (SAW) in den Supergittern zeigen, das Oberflachenphononen bei denselben beiden Modulationswellenlangen erweichen. Eine vorlaufige Erklarung der experimentellen Ergebnisse wird angegeben.

A note on Moore's interval test for zeros of nonlinear systems

Abstract: We study relations between Moore's interval test and Miranda's theorem. As an application we combine the (real) Newton iteration with a computational test for Miranda's hypothesis by Moore and Kioustelidis to find an approximate solution to the systemf(x)=0 with specified error bounds.

Density-density correlation functions and plasmons in tunnelling semiconductor superlattices

Abstract: The authors have studied the density-density correlation functions and plasmons in tunnelling semiconductor superlattices in the random-phase approximation, taking account of the overlap of the wavefunctions between adjacent quantum wells. Using the tight-binding wavefunctions, the electron-electron interaction and the density operator can be written as series of separable factors in matrix forms. The density-density correlation function can be explicitly expressed in a form consisting of multiplied matrices, and the plasmon dispersion relations are obtained. The crossover from 2D to 3D is shown.