Characteristics of a Negative Cloud-to-Ground Lightning Discharge Based on Locations of VHF Radiation Sources

The lightning very high frequency （VHF） radiation location system based on the short-baseline time-difference of arrival （TDOA） technique provides an effective approach to describe the temporal and spatial development of lightning discharge in two dimensions with high resolution. A negative single-stroke cloud-to- ground （CG） lightning flash was analyzed in detail using the radiation location results and synchronic fast/slow elec- tric field changes. The long-duration preliminary break- down process appeared to propagate with hi-directional leader channels. The two negative simultaneous discharge channels sloped down with a considerable horizontal com- ponent in the lower positive charge region at speeds of about 105 m s-1. The stepped leader was clearly converted from one channel of the preliminary breakdown process and spread downwards with branches. The speeds of the stepped leaders were about 105 m s -1. The K processes after the return stroke could either directly initiate from the start region with negative polarity lightning discharge, or initiate from a new region in the cloud as negative recoil streamers. All K processes propagated along the preceding electrified channel, while not all K processes initiated from the tips of positive breakdowns. The speeds of the K processes were about 106-107 m s-1.

Effect of acoustic pulses and EHF radiation on multipotent marrow stromal cells in tissue engineering constructs

In this paper,we studied the effects of physical factors,such as,acoustic pulses of laser-induced hydrodynamics(ALIH)and extremely-high frequencies(EHF)radiation,on the formation of heterotopic bone marrow organs.A suspension of precipitated bone marrow cells from CBA mice were exposed to ALIH pulses and EHF radiation separately and in their com bination tissue engineering constructs,presenting gelatin sponges 2 by 2 by 2 mm in size containing 10^(7)nucleated bone marrow cells,were exposed to physical factors and were implanted under the renal capsules of syngeneic mice.The newly formed hematopoietic organs were examined in three and five months later after treatment.The five months old transplants were bigger in size than the three months old transplants.The number of hematopoietic cells in the rest of the groups increased during this period by a factor from 3 to 10,the increase being as high as 20-fold in the:ALH+EHF group.Maximal concentration of multipotent stromal cells(MSCs)was in the EHF+ALIH,and minimal concentration was in the ALIH+EHF.The accumulation rate of bone capsule weight was highest for the transplants of EHF+ALIH and ALIH-sponge groups during the first three months.These data showed that the combined impact of the EHF+ALIH on MSCs is the most effective for the formation of bone marrow transplantation.

The high frequency acoustic radiation from the boundary layer of an axisymmetric body

The mechanism of acoustic radiation from the boundary layer of an axisymmetric body is analyzed, and its sound pressure spectrum is predicted. It is shown that the acoustic radiation results from the transition region and the turbulent boundary layer; and that the acoustic radiation from transition region is predominant at low frequencies; while the turbulent boundary layer has the decisive effect on acoustic radiation at high frequencies. The calculated values are in good agreement with the experimental data.