On the magnetic susceptibility of Pd1−x Ag x in the range 0.5≦x≦1

The weak variation of the magnetic bulk susceptibility of Pd_1–x Ag _x with temperature T and silver mole fractionx within 0.5x1 has been investigated in the range 5KT400K. Experimental evidence can be given for an intersection point of the susceptibility isotherms (T=const,x) atx=0.55. The observed dependence of on T andx is interpreted by means of a semiphenomenological alloy susceptibility function (T,x).     

Low temperature properties in Ce(Cu x Al1−x )5, [0.60≦x≦1.00]

We report on the formation of a heavy fermion state in Ce(Cu _x Al_1–x )₅, with 0.60x1.00. This state evolves upon the exchange of Cu by Al in the hexagonal CeCu₅. Furthermore, this exchange causes a suppression of a common type of long range magnetic order. Both phenomena are driven by Kondo interaction.     

57Fe Mössbauer studies in a new cluster spin glass system RuxFeGa (0.5≦x≦1.5)

⁵⁷Fe Mössbauer and bulk magnetization studies have been carried out in a new magnetic system Ru_xFeGa for 0.5x1.5. The system is seen to freeze into a cluster spin glass phase at 70 K. The freezing temperature and the hyperfine field at Fe at the lowest measured temperature, 190 kOe, is essentially same for all values of x investigated.     

57Fe Mössbauer investigations in the series Fe4−2xRuxSix(1.0≦x≦1.7)

⁵⁷Fe Mössbauer and magnetization studies on a new series Fe_4–2xRu_xSi_x (1.0x1.7) are reported. The system is seen to transform from a collinear ferromagnet for x1.2 to a cluster spin glass for x>=1.54 In the intermediate region the magnetic behaviour of the system, as probed by the Mössbauer effect, is dominated by the presence of clusters and their dynamics. The alloys have large ordering temperatures ( 750 K) throughout the series except for x>1.54 where they drop sharply. The moment values, in contrast, fall sharply from 4.8_B at x=1 to 0.5_B at x=1.6C. The average value of the HF at⁵⁷Fe measured at 15 K does not change significantly throughout the series.     

Beta-delayed proton precursors with 59≦Z≦62

The new, beta-delayed proton emitters¹²⁸Pr(3.2 _?0.4 ^+0.5 s),¹³⁰Pm(2.2 _?0.4 ^+0.6 s), and¹³²Pm(5.0 _?0.6 ^+0.8 s) have been observed at the on-line isotope separator OASIS. Also studied were¹²⁹Nd and¹³³Sm. Our on-going study of the decay properties of very neutron-deficient lanthanides has led to detailed information about beta-delayed proton emitters with 59≤Z≤62. The isotopes were produced at the SuperHILAC's on-line isotope separator OASIS [1] in reactions of⁴⁰Ca projectiles on⁹²Mo and⁹⁶Ru targets enriched to >95%. Decay studies were carried out in a low background spectroscopy laboratory. The isotope of interest was passed through a slit in the focal plane of the mass separator, transported ionoptically to a fast cycling tape, and periodically positioned between a silicon charged particle telescope, a HPGe x-ray detector, and a GAMMA-X Ge detector. Decays involving beta-delayed gamma rays and protons along with any coincident positrons, x-rays and gamma rays were measured event-by-event and written to computer tape for subsequent replay and analysis.     

IsoscalarE2 transition strengths in 10≦A≦48 nuclei

Electric quadrupole transition strengths for the 2 ₁ ⁺ ,T=1→0 ₁ ⁺ ,T=1γ-decay branches are summarized for 10≦A≦42 nuclei. In¹⁰B the corresponding branch has been remeasured by use of the⁹Be(p, γ)¹⁰B resonance reaction atE _p =320 keV; an upper limit of 0.6% is found. The variation of theE2 strengths within each individualT=1 isobaric multiplet reveals the particleor hole-character of the levels involved. The isoscalar 2 ₁ ⁺ →0 ₁ ⁺ transition strengths in 10≦A≦48 nuclei vary between 2 and 20 Weißkopf units showing drastic shell effects. Results for the ratio of neutron and proton matrix elements deduced from analogγ-decay studies and from inelastic pion scattering are compared.     

Proton and Two-proton Emissions from Proton-rich Nuclei with 10≦Z≦20

Proton (p) and two-proton (2p) emissions from the proton-rich nuclei with 10≦Z≦20 have been explored by the in-fight decay and implantation decay methods, respectively, in a series of experiments at the HIRFL-RIBLL facility. The in-flight 2p emissions from the excited states of 28,29S /26,27P and 17;18Ne were studied by complete-kinematics measurements. Mechanisms of 2p decay and related p-p correlations have been explored. Obvious 2p correlated emissions have been observed in the cases of 28,29S but not in 27,28P, indicating the 2p halo plays an important role in the diproton emission. In the 17;18Ne cases, a small 2p opening angles were deduced by the HBT analyses, implying the BCS-BEC crossover may occur in the dilute nuclear matter. Moreover, 27S/26P/25Si, 22Si/20Mg, 23Si/22Al/21Mg, 24Si/23Al, and 36;37Ca were implanted in a thin double-sided-silicon-strip detector and their -delayed p and 2p decays have been measured by a surrounding silicon detector array under the continuous-beam mode. Important information on the nuclear spectroscopy, such as energy, lifetime, branching-ratio, and so on, has been extracted, which helps us to understand the nuclear structures of proton-rich exotic nuclei close to the drip-line.     

Measurement ofK αcross sections and fluorescence yields for elements in the range 42≦Z≦57 using radioisotope X-ray fluorescence

TheK x-ray fluorescence (XRF) cross sections have been experimentally determined for elements in the range 42Z57 at excitation energy of 59.54keV associated with gamma rays of Am-241 radioisotope. In addition, measurements of XRF yields of theK shell (w _k) for the same elements at the same excitation energy have also been carried out. Our measurements were shown to agree with theoretical calculations.     

LaAg x In1−x

The structures of LaAg _x In_1–x alloys withx=0.75, 0.89 are determined by neutron diffraction on powder samples. The space group isI4/mmm (D _4h ^/17 ). The lattice constants splitting, the order parameter and the mean square vibrational amplitudes of the atoms are given in the temperature range from 20 KT300 K.     

Negatron effects in CdSe1 − x Te x and ZnS1−x Se x films

Various negatron effects in films of alloys of II–VI compounds deposited from solutions as a function of the deposition mode and heat treatment are studied. It is found that the negative photocapacitance effect, which was first discovered in ZnS_1?x Se _x films, and the slowly relaxing negative photoelectric effects, which are caused by the transition of electrons located in a nanoscale surface layer from the shallow energy levels of trapping centers to deeper levels with a lower polarizability and by the presence of nanoscale clusters in these materials, which play the role of a “reservoir” for minority charge carriers, occur according to a single mechanism. A model to explain the basic laws of negative photoconductivity in CdSe_{1 ? x} Te _x films deposited from a solution is proposed. Negative residual conductivity is explained in terms of double-barrier relief model, while negative differential photoconductivity is attributed to the presence of nanoscale electric domains.     

Plasmon dispersion in Al atk≦k F using electron energy loss spectroscopy

We find a quasi quadratic dispersion of the plasmon up to _p = 28 eV atk=1.77 Å^–1 with no levelling off contrary to other measurements. We usedk-scans at constant energy loss andE-scans at constant wave vector, which yield different dispersions of the plasmon peak maximum because of the finite halfwidth. The levelling off in plasmon dispersion observed previously is due to multiple scattering events, which obscure the plasmon dispersion inE-scans.We confirmed the anisotropy of the dispersion coefficient by investigating polycrystalline samples of different orientation.     

利用x|x|控制混沌系统

提出了一种新的混沌控制方法，即对混沌动力系统增加一个具有分段二次函数x|x|形式的非线性反馈控制器，利用它控制了一大类系统从混沌运动转化为各种规则的运动.该控制器是一种活动控制器，它不影响原系统的参数，其结构相当简单而且在物理、电路上都容易实现.数值仿真表明了该控制方法的有效性与可行性. 关键词： 混沌 非线性反馈控制器 分段二次函数     

BRST analysis of physical states for 2D gravity coupled toc≦1 matter

We consider 2D gravity coupled toc1 conformal matter in the conformal gauge. The Liouville system is represented by a free scalar field, ^L , with background charge such that the BRST operator imposing reparametrization invariance is nilpotent. We compute the cohomology of this BRST charge on the product of the Fock space of ^L with those of the ghosts and one other free scalar field, ^M representing the matter system. From this calculation the physical states of the full theory are determined. For thec<1 case the further projection from the Fock space of ^M to the irreducible representation, using Felder's resolution, reproduces the results of Lian and Zuckerman.Supported by the NSF Grant # PHY-88-04561Supported in part by the Department of Energy Contract # DE-FG03-84ER-40168 and by the USC Faculty Research and Innovation Fund     

Magnetism influenced by structural disorder in melt-spun DyMn6 − x Ge6 − x Fe x Al x (x = 2.5, 3)

Different chemical and/or geometrical orders were found in melt-spun DyMn_6???x Ge_6???x Fe _x Al _x with x = 2.5 and 3 having fully amorphous and mixed (crystalline and amorphous) structure, respectively. Thermal variations in magnetization M from liquid helium up to room temperature for both samples are similar. Magnetization value at zero field cooled curve reaches about 0.1 μ_B per formula unit at 2 K and then increases. Two maxima are visible, the first at 50 K (a sharp effect) and the second very broad ranging from 150 to 200 K. ⁵⁷Fe Mössbauer spectrometry investigation revealed a remaining magnetic component in addition to a prevailing quadrupolar feature. Application of a weak external magnetic field causes an increase in the mean hyperfine magnetic field B _hyp and the volume fraction of magnetic component. This observation was confirmed by results of M(T), M(H) and AC magnetic susceptibility measurements. In short-range ordered crystallographic zones characteristic of melt-spun DyMn_6???x Ge_6???x Fe _x Al _x (x = 2.5, 3) alloys, the related magnetic ordering, called the mictomagnetism or the cluster spin glass appears.     

Formation of Ti1–x Si x and Ti1–x Si x N films by magnetron co-sputtering

The paper reports on surface morphology, structure and microhardness of TiSi–N films formed by cosputtering from two target-facing unbalanced magnetrons, equipped with pure Ti and Si targets, on an unheated substrate rotating in front of both targets. The ratio Si/Ti in the TiSi–N film was achieved by modifying the magnitude of currents in the individual magnetrons and by the addition of nitrogen to the film. The rotation of the substrate has a strong effect on the film deposition rate and its morphology. The deposition rate is 3 times lower than that of the film deposited on a stationary substrate. The surface roughness of a polycrystalline Ti film deposited on the rotating substrate is considerably higher than that on a stationary substrate. On the contrary, the surface of an amorphous Si film is smooth and there is no difference between the roughness of Si films sputtered on stationary and on rotating substrates. The hardness of the film increases with increasing Si content and with the addition of nitrogen to the TiSi film. The Ti(26 at.%)Si(8.5 at.%)N(65 at.%)-film sputtered on an unheated rotating steel substrate, held at a floating potential, exhibited the best result with a hardness of 29 GPa.     

x射线探测器

Crystal 公司已研制出家用 x 及 x 射线探测器,其能量范围从4keV 到1MeV。CXM 系列探测器是基于 CsJ:T 闪烁晶体与 Si-Pin 光电二极管的结合产物,以电流模式工作。前置放大器是集成的,1meV～12V 的输出信号等效于 dosis 功率,该系列可作为单独的探测器和具有10mm 系统构形的线性探测器阵列使用。     

High-temperature ferromagnetism in Si1 ? x Mn x (x ≈ 0.5) nonstoichiometric alloys

It has been found that the Curie temperature (T _C ?? 300 K) in nonstoichiometric Si_{1 ? x} Mn _x alloys slightly enriched in Mn (x ?? 0.52?C0.55) in comparison to the stoichiometric manganese monosilicide MnSi becomes about an order of magnitude higher than that in MnSi (T _C ?? 30 K). Deviations from stoichiometry lead to a drastic decrease in the density of charge carries (holes), whereas their mobility at about 100 K becomes an order of magnitude higher than the value characteristic of MnSi. The high-temperature ferromagnetism is ascribed to the formation of defects with the localized magnetic moments and by their indirect exchange interaction mediated by the paramagnetic fluctuations of the hole spin density. The existence of defects with the localized magnetic moments in Si_{1 ? x} Mn _x alloys with x ?? 0.52?C0.55 is supported by the results of numerical calculations performed within the framework of the local-density-functional approximation. The increase in the hole mobility in the nonstoichiometric material is attributed to the decay of the Kondo (or spin-polaron) resonances presumably existing in MnSi.     

Effects of Nb and Y substitution on negative thermal expansion of ZrV 2−XPXO7 (0≦X≦0.8)

Zirconium vanadates with a novel chemical composition including niobium and yttrium were synthesized by the sol-gel method. An aqueous solution of NH₄H₂PO₄ and NH₄V O₃ and an ethanol solution of ZrOCl₂,NbCl₅, and Y Cl₃ were prepared. These two solutions were stirred and mixed to prepare precursors of zirconium vanadates at 333 K, following the evaporation of the solvent at 363 K. The precursor gels obtained were heated at 373-973 K in air. A zirconium vanadate phase began to crystallize above 673 K and a single phase of zirconium vanadate was synthesized at 973 K. Although ZrV ₂O₇ generally had a positive thermal expansion in the temperature range above RT, the degree of positive thermal expansion decreased with the two types of substitution of P for V and a set of Nb and Y for Zr of ZrV ₂O₇. X-ray diffraction peaks due to a superlattice structure, causing a positive thermal expansion from RT, were not observed in the synthesized (Nb, Y)-substituted zirconium vanadates.     

ВЛИЯНИЕ СОДЕРЖАНИЯ К ИСЛОРОДА НА ЭЛЕКТРИЧЕСКИЕ И ТЕ РМОЭЛЕКТРИЧЕСКИЕ СВОЙСТВА ТРОЙНОЙ СИС ТЕМЫ Вi2Те3−x Sе x

, Bi₂Te_3–x Se _x . , , . , , . .

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Influence of oxygen content on electric and thermoelectric properties of ternary system Bi₂Te_3–x Se _x

A study is made of the influence of oxygen, contained in the semi-conducting system Bi₂Te_3–x Sé _x , on the electric and thermoelectric properties. It is shown that the addition of oxygen to the prepared samples Bi₂Te_2.4Se_0.6 causes a decrease in electric conductivity while the thermoelectric force remains unchanged. This influence is connected with a decrease in the mobility of the electrons but their concentration is not influenced by the presence of oxygen. Conclusions are reached as to the influence of oxygen on the efficiency of the conversion of thermal energy into electric energy and vice versa.