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1.
Lattice dynamics seem to have little effect on the temperature dependence of the hyperfine field of pure iron and nickel and of most impurities in these metals but it is shown that Au in iron may be an exception to this rule. The hyperfine fields of other heavy impurities (FeRu,FeIr,NiPt) were found to have a normal temperature dependence. 相似文献
2.
Sum rules for the coupling constants for D (20), B (20′) and P (16) are given taking into account first order breaking of SU (4) and SU (3) symmetries. The D (20) and B (20′) contain the usual 3/2+ baryon decuplet and 1/2+ baryon octet of SU (3), while the P (16) contains the usual pseudoscalar octet of pions, etc. These sum rules generalize the decuplet → octet + octet sum rules of
broken SU (3 to a broken SU (4) symmetry scheme, in particular the charm SU (4) for hadrons. It is pointed out that, of the
many sum rules, it may be possible to check some of them experimentally (see Section 5) and thus provide a test for an underlying
SU (4 symmetry for strong interactions. 相似文献
3.
A. R. Arends C. Hohenemser R. M. Suter 《Zeitschrift für Physik B Condensed Matter》1980,37(3):203-208
Perturbed angular distribution (PAD) measurements of Bleck et al. of the critical behavior of63NiNi,66CuNi, and67ZnNi have been reanalyzed, and shown to be insufficiently asymptotic to permit deduction of meaningful critical exponents. Via experiments on implanted111InNi, done with and without annealing of radiation damage, and by comparison to diffused111InNi, it is suggested that unannealed radiation damage can produce serious systematic errors in critical exponents.This work has been supported in part by DMR 01250 from the U.S. National Science Foundation to Clark University, and in part by the Stichting voor Fundamenteel Onderzoek der Materie, the Netherlands 相似文献
4.
BaF2 scintillation counters, coupled to constant fraction differential discriminatiors, permit simultaneous energy and timing
decisions in recording delayed coincidence spectra. We explore the advantages and limitations of this innovation in time differential
perturbed angular correlation experiments, and illustrate it for111CdNi and100RhNi. 相似文献
5.
W. Lühr-Tanck H. Bosse Th. Kurschat M. Ederhof A. Sager Th. Hehenkamp 《Applied Physics A: Materials Science & Processing》1987,44(3):209-211
Positron annihilation measurements in pure copper and silver as well as in the alloysCuGe,CuIn,CuSb, andAgSb have been performed. Most of the measurements have been carried out in thermal equilibrium. In this way it is possible to deduce vacancy formation — and vacancy — solute atom binding energies. ForCuIn alloys with 3.3 at.% and 7.1 at.% indium precipitation effects have been studied.This paper is based upon a talk given by W.L.-T. at the Int. Symp. Production of Low-Energy Positrons with Accelerators and Applications Justus-Liebig-Universität Giessen (1986) 相似文献
6.
The measurement of QI frequencies at100Rh in Zr and Gd reveal that the electronic contribution to the EFG is quite large. The value of ¦K¦ is 8 for100RhZr whereas it is 45 for100RhGd. The temperature variation of100RhZr neither follows T1.5 nor has a linear T dependence. 相似文献
7.
H. M. Ajvazyan 《International Journal of Infrared and Millimeter Waves》1991,12(8):945-978
For the anomalous radar reflection from the oversized water drops originating in water-ice phase transition observable in the submillimeter band transparency window of ice [1] we consider the process of extinction, scattering, and absorption in a cloud and atmosphere. Our calculations, which are based on experimental results, show that in the situation when the convective cloud is illuminated from nadir by a narrow-beam submillimeter radar (carried on board an airplane or a satellite), the total extinction and absorption in the cloud and atmosphere is nearby 20dB in the long-wave transparency window of atmosphere. In the central part of submillimeter band these losses may be as high as 40dB.However,the
level
of
losses
has
no
effect
on
a
difference
between
the
radar
reflection
coefficients for overcooled water and ice existing due to phase transition, and this difference may be over 20dB in the 0.3 to 0.8mm ice transparency window. 相似文献
8.
The electron scattering by short-wavelength and long-wavelength phonons in (GaAs)
m
(AlAs)
n
(001) superlattices with ultrathin layers (n, m = 1, 2, 3) has been investigated using the pseudopotential method and the phenomenological model of bonding forces. The deformation
potentials have been found for intervalley electron transitions in the conduction bands of the superlattices and solid solutions
of the corresponding compositions. It has been shown that, owing to the localization of the wave functions in the quantum
wells Γ, L, and X, the intensity of intervalley electron transitions in the superlattices, as a whole, is higher than that of similar transitions
in the solid solutions. As the content of light Al atoms in the superlattices increases, the deformation potentials monotonically
increase for the X-X transitions and decrease for the L-L and X-L transitions. The potentials of the Γ-X and Γ-L transitions change nonmonotonically depending on the layer thickness due to the pronounced quantum-well effects in the deep
Γ quantum wells of GaAs. The deformation potentials averaged over phonons and related valleys in the superlattices are close
to the corresponding potentials in the solid solutions. 相似文献
9.
Valence and core level spectra ofAgMn,AuFe,AuCo,AuNi,CuFe,CuCo andCuNi will be reported. Clearly defined virtual bound states (vbs) can only be detected in the spin fluctuating systemsAuNi andCuNi. An increase in the density of states near the Fermi energy, in the region of the flats-p band of the host metal is observed in the other magnetic alloys. There are indications that a large hybridization between the impurity and the host metald-electrons exist. The impurity core levels show satellites. They can originate from the emission from real isolated impurities and from many body effects. 相似文献
10.
P. Steiner H. Höchst W. Steffen S. Hüfner 《Zeitschrift für Physik B Condensed Matter》1980,38(3):191-199
The core and valence band spectra of diluteAlMn,AlNi andAlCu alloys have been investigated by x-ray induced photoemission spectroscopy (XPS). The 2p levels of Mn and Cu inAlMn andAlCu change only slightly compared to their properties in the pure metals, whereas those of Ni inAlNi lose both their asymmetry and the two hole satellite. The 3s spectra of Mn inAlMn show a splitting of 2.9 eV, as compared to 4.3 eV in Mn metal. This indicates that inAlMn the Mn ion is magnetic, at least in the time scale of the XPS measurement. The valence band spectra of the alloys (and ofAlFe andAlCo) show virtual bound states with a width of about 1.5 eV and a distance relative to the Fermi energy which increases with increasingd-occupancy. The energy of the Al plasmons increase with increasingd-metal content. 相似文献
11.
M. Budzyński P. Simecek T. Lesner P. Giźek I. Prochazka E. Simeckova V. M. Tsupko-Sitnikov L. Ehn Z. Janout 《Hyperfine Interactions》1987,34(1-4):315-318
Hyperfine magnetic fields for such probes as:152SmFe,152SmCo,152SmNi,155GdFe,172YbFe,172YbCo and172YbNi have been measured using PAC method. The quantitative analysis of components of these fields has been also performed. 相似文献
12.
P. Herzog 《Hyperfine Interactions》1990,60(1-4):563-579
For samples prepared by ion implantation the dependence of the hyperfine interaction on parameters as implantation temperature,
implantation dose and enthalpy of solution of the impurity-host system is discussed. Results from static low temperature nuclear
orientation and nuclear magnetic resonance of oriented nuclei experiments with the system BiFe, CsFe, AuFe, BrFe, BrCo and IFe are presented and where possible compared with recent systematic channeling results. 相似文献
13.
Summary Ho in Au exhibits interesting paramagnetism. The full J=8 angular momentum is partially quenched by the crystal field. At sufficiently low temperatures, however, the ion acts like a Van Vleck paramagnet although it has a non-magnetic doublet at ground state instead of a singlet ground state. An applied magnetic field definitely is enhanced by the large hyperfine interaction and excited ground state mixing. This results in anisotropy all the way up to 1 K which makes166m HoAu an excellent candidate for a secondary thermometer in the 10mK-1 K region. The complete interpretation of the166m Ho3+
Au experiments will require sizeable computing times. 相似文献
14.
Abstract Coherent anti-Stokes Raman spectroscopy, or CARS as it has come to be known, is a relatively new spectroscopic technique which has gained considerable interest over the past few years because of its potential use as a powerful analytical tool and because of its unique and curious properties [1–98], Several review articles on the subject have been written recently [4, 30, 33, 35, 49, 67, 72, 90]. Some papers have attempted to describe the theoretical background [30, 33] and others have surveyed the entire subject matter [4, 35, 49, 67, 72, 90]. In this report we will review only CARS spectroscopy of gases. However, because of recent progress it might be well to at least reference some new results [18–21, 42, 47, 66] in resonance and “normal” CARS of biological and fluorescent materials in dilute solution (as low as ~ 10?7 M). Moreover, since the emphasis of this paper is on applications, we will not attempt to derive the theory or the principles behind CARS but merely describe the results. 相似文献
15.
The low field Hall coefficient of a number of polycrystalline foils of dilute (2%) alloys of copper and silver has been measured
in the temperature range 1.5–50°K, and at room temperature. The alloys chosen wereCu-Au andAg-Au (uncharged impurity),Cu Ge andAg-Sn (charged impurity), andCu-Ni andAg-Pd (transition metal impurity).
At 20°K and below, the Hall coefficients of the different copper alloys differ widely from each other,Cu-Ge giving the highest (negative) values (up to twice the room temperature value for pure copper), andCu-Au the lowest (down to 0.7 of this value). There are also significant concentration dependences. The silver alloys show corresponding
but smaller changes.
A relationship, due to Tsuji, gives the Hall coefficient as a function of the Fermi velocityν and the mean curvature 1/ϱ of the Fermi surface, for the case of an isotropic relaxation time. The integrals over the Fermi surface have been numerically
estimated using the known Fermi surface and electron velocities. For both Cu and Ag the results agree with the experimental
room temperature values, which we take as evidence thatτ(k) for phonon scattering is here close to isotropic.
On the other hand, to account for the Hall coefficients of the alloys, it is necessary to assume that the relaxation timeτ varies over the Fermi surface.
It is seen that in Cu and Ag the neck regions contribute relatively little toR since both 1/ϱ andν are small there. The main change inR in different alloys arises from the variation in the relative weighting given to the belly regions by different kinds of
impurity scattering. A closer analysis shows that the bulges in the Fermi surface of copper in the 〈100〉 directions contribute
relatively heavily because of their high positive curvature.
The anisotropy ofτ deduced from the Hall coefficient is compared with that deduced from other measurements. 相似文献
16.
D. H. Chaplin W. D. Hutchison M. P. Kopp N. Yazidjoglou 《Hyperfine Interactions》1988,43(1-4):241-247
Electric quadrupole interactions of impurity nuclei in single crystals of54MnNi,125SbNi and125SbFe have been studied as a function of crystal field direction and applied magnetic field using MAPON. Distributions are in all
cases broad compared with the mode values of the EQI's. For54MnNi the mode efg is isotropic to better than 5% between the easy <111> axis and a hard <100> axis. The efg is +0.88 (15)x 1019 Vm−2. The mode efg for125SbFe along its easy <100> axis is one half of that along a hard <112> axis, and one third of that measured along the easy <111>
axis of125SbNi. The much larger efg mode and distribution seen in125SbNi, for four to eight times greater dilution than for125SbFe, suggests intrinsic contributions due to valence screening effects in the more itinerant nickel host. 相似文献
17.
Nuclear magnetic resonance on oriented76,77,82BrFe has been measured using recoil-implanted samples. The magnetic hyperfine splitting frequency of82BrFe in a zero external magnetic field has been determined to be 201.90(3) MHz. The resonances of76BrFe and77BrFe were also observed in an external magnetic field of 0.2 T asv(76BrFe)=340.9(3) MHz andv(77BrFe)=403.5(2) MHz. With the known values of theg-factors, the hyperfine fields have been deduced:B
HF(82BrFe)=81.397(27) T,B
HF(76BrFe)=81.38(7) T. Theg-factor of77Br was determined to be |0.6487(4)|. 相似文献
18.
The magnetic hyperfine splitting frequencies of90NbNi and93mMoNi in an external magnetic field of 0.2 T have been determined by the NMR-ON method to be 18.52(7) and23.73(10) MHz, respectively. With the assumption of Knight shift factorK=0 and with the knowng-factors, the hyperfine fields of90NbNi and93mMoNi were deduced asB
HF(90NbNi)=-4.118(16) T andB
HF(93mMoNi)=-3.491(33) T. The rather long spin-lattice relaxation time of 32(5) min was observed for90NbNi at an external magnetic field of 0.2T and8 mK. 相似文献
19.
Background
Brevican is a member of the lectican family of aggregating extracellular matrix (ECM) proteoglycans that bear chondroitin sulfate (CS) chains. It is highly expressed in the central nervous system (CNS) and is thought to stabilize synapses and inhibit neural plasticity and as such, neuritic or synaptic remodeling would be less likely to occur in regions with intact and abundant, lectican-containing, ECM complexes. Neural plasticity may occur more readily when these ECM complexes are broken down by endogenous proteases, the ADAMTSs (a disintegrin and metalloproteinase with thrombospondin motifs), that selectively cleave the lecticans. The purpose of these experiments was to determine whether the production of brevican or the ADAMTS-cleaved fragments of brevican were altered after deafferentation and reinnervation of the dentate gyrus via entorhinal cortex lesion (ECL). 相似文献20.
F. N. Gygax E. Lippelt A. Schenck A. J. van der Wal S. Barth 《Hyperfine Interactions》1986,31(1-4):447-453
In continuation of our earlier studies of the anomalous temperature dependence of the μ+ Knight shift Kμ in Cd,CdHg (1.2 at %) andCdMg (3.38 at %) — interpreted as due to Van Hove-type singularities in the local density of electron states /1/ — we have studied
the temperature dependence of the μ+ Knight shift in polycrystallineCdMg (1.04 at %, 2.05 at %) and in a single crystal ofCdMg (2.5 at %). In contrast to pure Cd no anisotropies in Kμ could be detected. The temperature dependence of Kμ in aCdMg (2.05 at %) sample and in the monocrystallineCdMg (2.5 at %) sample essentially reproduces the one previously observed in polycrystallineCdMg (3.38 at %), showing a steplike discontinuity and a logarithmic singularity. A complete different behaviour is observed
inCdMg (1.04 at %), where no logarithmic singularity seems to show up and where a steplike discontinuity of opposite sign at around
90 K is clearly seen. If these singularities are still to be interpreted in terms of Van Hove singularities, the question
arises why there is such a nonlinear dependence on the Mg concentration. 相似文献