Possible Mechanism For Loss Research Articles

Losses of high-intensity optical radiation in transparent nonlinear media

One of the possible mechanisms of loss of energy by high intensity optical radiation in media with a quadratic nonlinearity is considered. The source of losses is nonphase-matched second-harmonic generation when the doubled frequency lies within an absorption region of a crystal. A detailed study is reported of the influence of absorption at the second-harmonic frequency on the propagation of the fundamental-frequency wave for different ratios of the characteristic lengths (absorption, nonlinear, coherence, and quasistatic). It is shown that in some cases nonlinear losses of the fundamental-frequency radiation may be considerable and can limit the efficiency of phase-matched nonlinear optical processes.

Atomistic study of structural metastability in coherently strained Si-like layers.

Comparison of experimental values for critical mismatch of coherently strained semiconductor films with the predictions of equilibrium theories suggests that metastable structures with much greater critical mismatch than predicted by equilibrium theory can often be grown in practice. One possible mechanism for loss of coherence in such metastable structures is the generation of misfit dislocations in an initially perfect overlayer by nucleation of half-loop of misfit dislocation at the surface of the strained layer. The mismatch threshold for zero-temperature loss of coherence associated with this half-loop dislocation nucleation mechanism, which does not occur in the continuum model, is calculated using atomistic Monte Carlo techniques on a coherently strained layer composed of a model siliconlike material. The instability threshold for a 10-A\r{}-thick layer is found to be 11.2%, compared to the equilibrium critical mismatch of about 4%. Possible extensions of this approach to the problem of practical stability of coherently strained structures are discussed.

Corticospinal neurons 25 weeks after right hind limb amputation

Neuronal cell death in embryos and adult animals is seen after removal of target tissue. Transsynaptic cell death has been described in the mammalian visual system and suggested as a possible mechanism for loss of upper motor neurons in amyotrophic lateral sclerosis. We previously demonstrated that amputation of a hind limb decreased the number of motor neurons in the rat spinal cord. Careful counts of corticospinal neurons in these rats 25 weeks after amputation failed to demonstrate any loss of corticospinal neurons. Although amputation caused a loss of ventral horn neurons, no subsequent loss of upper motor neurons was detected at 25 weeks.

Accumulation of copper, lead and arsenic in some Australian orchard soils

A survey was made of copper, lead and arsenic in 98 surface soils from orchards in South Australia and Tasmania and the distribution of these elements in six representative soil profiles was studied. Copper, lead and arsenic have accumulated in the soils due to the use of sprays. Concentrations were found which were 25-35 times greater than background values. Investigation of the profiles indicated that copper and lead have been strongly retained in the upper parts of the profiles, but arsenic can be lost. Possible mechanisms for loss of arsenic are discussed. Copper and lead extracted by DTPA and EDTA were highly correlated with 'total' concentrations determined on aqua regia digests. No relationships were evident between the concentrations of copper, lead and arsenic in former orchard soils and the concentrations in ryegrass and white clover.

Loss of rat ventricular α1-adrenergic receptors during aging

Ventricular α 1-adrenergic receptor concentration, measured by specific binding of [ 3H]-prazosin, decreases by 33% as rats age from 3 to 24 months. No age changes occur in binding affinity for [ 3H]-prazosin or potency of various α-adrenergic agonists and antagonists to displace [ 3H]-prazosin. The ratio of membrane protein to ventricular wet weight also does not change significantly with age. These results suggest a possible mechanism for loss of cardiovascular α-adrenergic responsiveness during aging.

Inorganic nitrogen movement in tropical soils

Abstract The movement and recovery of ammonium nitrogen down the profile of a fallow clay soil with poor drainage were studied during the rainy season in the Philippines. Cylinders were either covered by film or uncovered to determine the effect of rain. After 4 months with a total rainfall of 850 mm, 20 and 40% of the applied 15N was recovered from the 0-75 cm soil in uncovered and covered cylinders. Downward movement of 15N was found in both covered and uncovered cylinders. The 15N content of the soil layers lower than 45 cm depth, where soil was frequently submerged, was nealigible. A similar experiment was conducted in a dryland clay-loam soil with better drainap. After 5 months with a total rainfall of 890 mm, 24 and 63% of the applied 15N was recovered from the 0-75 cm soil in uncovered and covered cylinders. Labeled nitroaen was traced up to the 75 cm depth in both cylinders. In uncovered cylinders, downward movement of 15N as mineral nitrogen was more pronounced in the well-drained than in the poorly drained soil, while the reverse was the case in the covered cylinder. The observed difference in nitrogen recovery in two dryland soils is discussed in terms of possible mechanisms of loss.

Permanent loss of chromosome initiation in toluene-treated Bacillus subtilis cells.

Initiation of deoxyribonucleic acid replication is absent in Bacillus subtilis cells made permeable by toluene. The absence of initiation may be (i) a temporary removal of toluene, or (ii) irreversibly lost due to damage by toluene treatment to a cellular structure or a process required for chromosome initiation. Washed cells, previously treated with toluene and subsequently washed free of detectable amounts of toluene, have the same characteristics of toluene-treated cells in which toluene is not removed. The continued absence of initiation in the washed cells indicates a permanent loss of initiation in cells treated with toluene. Protein synthesis is also inhibited irreversibly by toluene treatment, indicating damage to translation as a possible mechanism for loss of initiation of toluene-treated cells.

Prevention of SV40 virus tumorigenesis by irradiated, disrupted and iododeoxyuridine treated tumor cell antigens.

SummaryHamster SV40 tumor cells rendered nonproliferative by exposure to gamma rays or by propagation in the presence of iododeoxyuridine were highly effective when used as immunizing antigens for preventing the appearance of tumors in hamsters which had received SV40 virus when newborn. Only a single injection of immunizing antigen was employed. Disruption of tumor cell preparations by freeze-thaw or by treatment in a French pressure cell for purpose of fractionation resulted in total or near total loss of immunizing capability, even when incorporated into alum adjuvant. Possible mechanisms for loss of potency are discussed.Addendum: Since the time the present manuscript was in press, it was found in further experiments employing the same techniques that the loss of RNA and protein following cell disruption was considerably less than noted above.