Free-carrier multiphoton laser absorption in magnetic semiconductors

The magnon scattering by free carriers in the presence of an intense laser field is discussed. A kinetic equation for electrons is derived from which the multiphonon absorption coefficient is calculated. It is found that for very large fields the absorption coefficient is vanishing small. A physical explanation of this result is also available.     

Magnon instability in the free-carrier absorption in magnetic semiconductors under a strong d.c. magnetic field

The magnon damping in an electron-magnon system in the presence of a laser beam and a d.c. magnetic field is discussed. It is shown that near the laser-cyclotron resonance, and for the laser beam propagating perpendicularly to the magnetic field the magnon population in a relatively narrow range of k may grow with time.     

Spin wave amplification by a radiation field in free-carrier magnetic semiconductors

The rate of change in the magnon population due to scattering by free carriers in the presence of a laser field is calculated. It is found that spin waves propagating parallel to the direction of propagation of the radiation field may be amplified over a relatively narrow band of q values.     

L 0 - phonon instability in the free-carrier absorption in semiconductors under strong magnetic fields

The LO- phonon damping in an electron-phonon system in the presence of a laser beam and a d. c. magnetic field is discussed. It is shown that near the laser-cyclotron resonance, and for the laser beam propagating perpendicularly to the magnetic field the LO-phonon population in a relatively narrow range of $\text{K}$ may grow with time.     

Synthesis and spectroscopic characterization of copper(II) tetraazaiminooxime macrocyclic complexes--a tetragonal distortion analysis

Herein we describe the synthesis and spectroscopic (infrared and UV-vis) analysis of [Cu(II)(dohpn)(L)](n+) (dohpn=imineoximic tetraazamacrocyclic ligand 2,3,9,10-tetramethyl-1,4,8,11-tetraazaundecane-1,3,8,10-tetraen-11-ol-1-olate) and L=SCN(-), I(-), Cl(-) (n=0) and 4-aminopyridine (ampy), 4,4'-bipyridine (bipy), imidazole (im), 2-aminopyrazine (ampz) and water (n=1+). The following order of the Jahn-Teller stabilization energy (cm(-1)) was observed: I(-)(6452)相似文献   

Synthesis, characterization and semi-empirical calculations for the thiocyanate linkage isomers of an (alpha-iminooxime)cobalt(III) macrocyclic complex

Herein we report the synthetic route and detailed characterization of the macrocyclic complex [Co(dohpn)(SCN)2] and its linkage isomer (dohpn=2,3,9,10-tetramethyl-1,4,8,11-tetraazaundecane-1,3,8,10-tetraen-11-ol-1-olate and py=pyridine) based on analytical, spectroscopic and electrochemical methods. Structural, vibrational and electronic features are discussed and a coherent assignment is proposed on the basis of semi-empirical theoretical calculations.     

Energy decay and control for a system of strings elastically connected in parallel

In the present paper, we study energy decay and exact boundary controllability for a system of n one-dimensional linear wave equations coupled in parallel. The control obtained is a square integrable of the Neuman type for initial data with finite energy. The controllability time is near optimal value. We treat the case of control in the whole boundary and also in part of it.     

Error Bounds for Low-Rank Approximations of the First Exponential Integral Kernel

A hierarchical matrix is an efficient data-sparse representation of a matrix, especially useful for large dimensional problems. It consists of low-rank subblocks leading to low memory requirements as well as inexpensive computational costs. In this work, we discuss the use of the hierarchical matrix technique in the numerical solution of a large scale eigenvalue problem arising from a finite rank discretization of an integral operator. The operator is of convolution type, it is defined through the first exponential-integral function and, hence, it is weakly singular. We develop analytical expressions for the approximate degenerate kernels and deduce error upper bounds for these approximations. Some computational results illustrating the efficiency and robustness of the approach are presented.     

Antidiarrhoeic effect and dereplication of the aqueous extract of Annona crassiflora (Annonaceae)

We investigated the antidiarrhoeic effect of the aqueous extract of Annona crassiflora leaves (AEAC). The AEAC decreased the diarrhoeic stools and enteropooling induced by castor oil, without altering total faecal output; moreover, the distance travelled by charcoal meal in the intestine was increased. Twenty-eight compounds were identified by LC-DAD-MS in the AEAC, including flavonoids, alkaloids and proanthocyanidins. In addition, two oligomeric series of condensed tannins of up to nine flavan-3-ol units were characterised by MALDI-MS. These data suggest that the antidiarrhoeic effect of the AEAC is related to its ability to inhibit intestinal secretion and/or to increase intestinal absorption. Moreover, the prokinetic effect of AEAC, together with its inhibitory effect on enteropooling induced by castor oil, explains why this extract decreased diarrhoeic faeces without altering the total faecal output. All these effects are in agreement with the pharmacological activity reported in the literature for many of the secondary metabolites identified.