Multiple Valleys Research Articles

The electronic band structure of Pb1-xSnxTe alloys. I. Cubic and rhombohedral phase at 4.2K

The Fermi surfaces of Pb1-xSnxTe in the cubic and rhombohedrally distorted phases for both normal and inverted band structures have been investigated using the Shubnikov-de Haas effect. Comparison of the observed Fermi-surface cross-sectional areas with the band structures of Dimmock (1981), for the cubic phase, and of Bangert (1981), for the rhombohedral phase, yield parameters which are in agreement with values established previously for the cubic phase. The complex character of the Fermi surfaces at the points T and L in the rhomobohedral Brillouin zone is found to agree with the predicted splitting of the ellipsoids of the cubic phase into the 'skin' and 'core' of an apple-like composite surface, originating in the lifting of the inversion symmetry of the structure in the structural phase transition. Clear evidence is obtained for the presence of structural domains in the rhombohedral phase. The carrier concentrations deduced from the Fermi-surface volumes are found to agree with those measured from the weak-field Hall coefficients, when account is taken of the anisotropy of the multiple carrier valleys in the band structure.

A stabilized source for supplying a superconducting magnet

The aim of this study is to investigate the flow field characteristics in ABL (Atmospheric Boundary Layer) flow over multiple hills and valleys in two-dimensional models under neutral conditions. Active turbulence grids and boundary layer generation frame were used to simulate the natural winds in wind tunnel experiments. As a result, the mean wind velocity, the velocity vector diagram and turbulence intensity around the hills were investigated by using a PIV (Particle Image Velocimetry) system. From the measurement results, it was known that the average velocity was increased along the upstream slope of upside hill, and then separated at the top of the hills, the acceleration region of U/Uref > 1 was generated at the downstream of the hill. Meanwhile, a large clockwise circulation flow was generated between the two hill models. Moreover, the turbulence intensity showed small value in the circulation flow regions. Compared to 1H model, the turbulence intensity in the mainstream direction showed larger value than that in the vertical direction. This paper provided a better understanding of the wind energy distribution on the terrain for proper selection of suitable sites for installing wind farms in the ABL.

A rapid assay of dipolar and extradipolar content in the human electrocardiogram

Summary o 1. A rapid iterative method has been developed for the calculation of the surface potentials on a bounded homogeneous torso shape resulting from a dipole of known size, orientation and site in the heart region. In essence, the approach is a convergent search for a potential distribution which will reduce to the desired dipole upon Gabor-Nelson surface integration. 2. This means of obtaining the surface effect of a dipolar generator has been applied to the specific problem of finding a series of surface voltages resulting from 18 instantaneous equivalent dipoles during the QRS complex in 25 normal young men. 3. In these normal subjects, the dipolar components of surface electrocardiographic potential had an average relative magnitude of .90 compared with whole real surface potential distribution, whereas the residual extradipolar component had an average relative magnitude about one-half this or .44. 4. There is a continuous extradipolar component throughout the QRS complex which is proportional in magnitude to the surface potential. It is not synomymous with multiple peaks and valleys seen in body surface maps; the latter is an easily visible special instance of “multipolar effect. While extradipolar component includes such peaks and valleys, it is a quantifiably comprehensive statement of total multipolar effect.

Signal Processing to Reduce Multipath Distortion in Small Rooms

The transmission between a sound source and a microphone in a small, hard-walled room is characterized by multiple peaks and sharp valleys. Sound received by such a microphone often is judged to be undesirably distorted or spectrally colored. Speakerphones and conference telephony systems are vulnerable to this acoustic distortion. A technique is described for combining the signals from two or more microphones to produce a single output having less multipath distortion than any of the individual microphone signals. The output from each microphone is filtered into a number of bandpass signals occupying contiguous frequency ranges. The microphone receiving greatest average power in a given frequency band contributes that signal band to the output. Each microphone, then, is used only for those frequency bands in which its received power is greater than any other microphone, so that the combined output contains less spectral coloration than the signal from any individual microphone. The processing method is studied by simulation on a digital computer. Broad-band noise and speech signals are used to test the method.

Signal Processing to Reduce Multipath Distortion in Small Rooms

The transmission between a sound source and a microphone in a small hard-walled room is characterized by multiple peaks and sharp valleys. Sound received by such a microphone often is judged to be undesirably distorted or spectrally colored. A technique is described for combining the signals from two or more microphones to produce a single output having less multipath distortion than any of the individual microphone signals. The output from each microphone is filtered to separate it into a number of bandpass signals occupying contiguous frequency bands. The microphone with greatest long-time response in a given frequency band contributes that band to the output. Each microphone, then, is used only for those frequency bands in which its response is greater than any other microphone, so that the combined output contains less spectral coloration than the signal from any individual microphone. The performance of the process was studied by simulation on a digital computer, and sample recordings are included.