Amplification of a terahertz wave via stimulated Raman scattering

Extremely strong terahertz (THz) waves are desperately demanded for investigating nonlinear physics, spectroscopy, and imaging in the THz range. However, traditional crystal-/semiconductor-based THz sources have limitations of reaching extremely high amplitude due to the damage threshold of devices. Here, by introducing Raman amplification to the THz range, we propose a novel, to the best of our knowledge, scheme to amplify THz waves in plasma. A long-pulse CO₂ pump laser transfers its energy to a multicycle, 10-THz seed in a two-step plasma. By one-dimensional simulations, a 0.87-GV/m, 1.2-ps-duration THz seed is amplified to 10 GV/m in a 5.7-mm-long plasma with an amplification efficiency approaching 1%. The method provides a new technology to manipulate the intensity of THz waves.

k-space theory and convective gains of stimulated Raman side scattering

We have developed a k-space theory for stimulated Raman scattering. The theory is used to calculate the convective gain of stimulated Raman side scattering (SRSS) in order to clarify the discrepancies found between previous gain formulas proposed in the literature. The gains are dramatically modified by the eigenvalue of SRSS, and the maximum gain occurs not at the perfect wave-number matching condition but instead at a wave number having a small deviation that is associated with the eigenvalue. Numerical solutions of the k-space theory equations are compared with, and used to verify, analytically derived gains. We demonstrate connections to the existing path integral theories, and we derive a similar path integral formula in k space.

Enhanced strong-coupling stimulated Brillouin amplification assisted by Raman amplification

Higher intensity of strong-coupling stimulated Brillouin scattering (SC-SBS) amplification is achieved by supplementary Raman amplification. In this scheme, a Raman pump laser first amplifies the seed pulse in the homogeneous plasma, and then a SC-SBS pump laser continues the amplification in the inhomogeneous plasma in order to suppress the spontaneous instability of pump lasers. The intensity of the seed laser gets higher and the duration of the seed laser gets shorter than that in the pure SC-SBS scheme with the same incident energy, while the energy conversion efficiency is not significantly reduced. We also found that the SC-SBS amplification is seeded by the leading pulse of Raman amplification. The results obtained from envelope coupling equations, Vlasov simulations, and two-dimensional particle-in-cell simulations agree with each other. This scheme offers a possible way to improve the SC-SBS amplification in experiments.

Absolute stimulated Brillouin side scattering in an inhomogeneous flowing plasma

Theory of absolute stimulated Brillouin side scattering in an inhomogeneous flowing plasma is presented and verified numerically. The linearized coupling equations are transformed into a Schrödinger equation in k space and solved as an eigenvalue problem. Analytic threshold, growth rate, and scattering geometry are obtained for the pump laser with arbitrary incidence angle. Numerical solutions of the coupling equations show good agreements between the theoretical and numerical absolute thresholds when ion-acoustic wave damping is not too large, and thus an old but famous threshold in [Phys. Fluids 17, 1211 (1974)PFLDAS0031-917110.1063/1.1694867] is corrected. It also indicates that the theoretical analysis is not accurate for strong dampings, since it will overestimate the absolute threshold. Possibility of finding such instability in the current experiments is also discussed.

Growth and saturation of stimulated Raman scattering in two overlapping laser beams

Two-dimensional particle-in-cell simulations are presented of the linear and nonlinear developments of stimulated Raman scattering in two overlapping laser beams. The development of the most unstable mode in the linear stage is consistent with a previous paper [C. Z. Xiao et al., Phys. Plasmas 26, 062109 (2019)PHPAEN1070-664X10.1063/1.5096850] where SL mode (two beams share a common scattered light) is dominant in the overlapping region. This mode is enhanced with plasma density and correlation of beam polarizations. When lasers are cross-polarized, it backs to the single-beam Raman backscattering with weak intensity. Trapping-induced nonlinear frequency shift leads to the saturation of SL mode by detuning the coupling and broadening the spectrum. An interesting result that SL mode becomes stronger as the incidence angle increases is contrary to the theoretical prediction and it is a consequence of less efficient saturation in the nonlinear stage.

[One case of pyoderma gangrenosum in the lower limbs in Tibetan Plateau treated with vacuum sealing drainage combined with irrigation of oxygen loaded fluid]

A 54 years old male patient with chronic leg ulcers was admitted in our hospital in November 2017. He was diagnosed as pyoderma gangrenosum by the pathological examination. Then the wound was treated with simple vacuum sealing drainage combined with irrigation of oxygen loaded fluid. This therapy overcame the shortage of hypoxia in the Tibetan Plateau on wound healing, resulting in a better wound healing. The patient was eventually cured and discharged from hospital.

[Advances in the research of effects of autologous platelet-rich plasma on the treatment of burn wounds]

Autologous platelet-rich plasma (PRP) is plasma with high concentration of platelet extracted from autologous blood. After activation, growth factors involved in wound healing are released from PRP. Current clinical investigations have demonstrated that the application of PRP seems to enhance the clinical outcome of plastic surgery, oral implantology, maxillofacial region and bone repair, and cardio-thoracic surgery. PRP can stimulate angiogenesis and promote fibroblast proliferation, therefore the application of PRP has shown good results in wound healing. However, up to date there is few current clinical researches on application of PRP on wound healing in burn patients. The application of PRP is not currently standardized, and the effects in burn wounds are poorly understood. This review is to determine if the application of PRP can enhance the clinical outcome of burns and scar formation.

Fluid nonlinear frequency shift of nonlinear ion acoustic waves in multi-ion species plasmas in the small wave number region

The properties of the nonlinear frequency shift (NFS), especially the fluid NFS from the harmonic generation of the ion-acoustic wave (IAW) in multi-ion species plasmas, have been researched by Vlasov simulation. Pictures of the nonlinear frequency shift from harmonic generation and particle trapping are shown to explain the mechanism of NFS qualitatively. The theoretical model of the fluid NFS from harmonic generation in multi-ion species plasmas is given, and the results of Vlasov simulation are consistent with the theoretical result of multi-ion species plasmas. When the wave number kλ_{De} is small, such as kλ_{De}=0.1, the fluid NFS dominates in the total NFS and will reach as large as nearly 15% when the wave amplitude |eϕ/T_{e}|∼0.1, which indicates that in the condition of small kλ_{De}, the fluid NFS dominates in the saturation of stimulated Brillouin scattering, especially when the nonlinear IAW amplitude is large.

Purified cholera toxin B subunit from transgenic tobacco plants possesses authentic antigenicity

Cholera toxin B subunit (CTB) mature protein was stably expressed in transgenic tobacco plants under the control of the CaMV 35S promoter and TMV Omega fragment. Fusion of the PR1b signal peptide coding sequence to the CTB mature protein gene increased the expression level by 24-fold. The tobacco-synthesized CTB (tCTB) was purified to homogeneity by a single step of immunoaffinity chromatography. The purified tCTB is predominantly in the form of pentamers with molecular weight identical to the native pentameric CTB, indicating that the PR1b-CTB fusion protein has been properly processed in tobacco cells. Furthermore, by immunodiffusion and immunoelectrophoresis, we have shown that the antigenicity of the purified tCTB is indistinguishable from that of the native CTB protein.

[Production of u-PA with rCHO cell culture on porous microcarriers in serum-free growth medium]

A novel technique was developed to deal with apoptosis in large-scale animal cell culture. By means of replacing part of Cytopore porous microcarriers at regular intervals, a rCHO cell line, which produces urokinase-type plasminogen activitor(u-PA), was cultivated continuously with serum-free medium in a 30 L stirred tank for 91 days. The cell density was maintained at (1.3-2.6) x 10(7)/mL, and > 90% of cells was viable. In order to reduce the effect of cell density on cell growth and expression, a cyclic pressure oscillation was exerted on a 7.5 L reactor headspace to enhance cell expression at high cell density to a certain extent. During the 67 days of medium-replacement culture, the maximal cell density reached 2.64 x 10(7)/mL, and cell viability was always kept above 95% when combined with microcarrier-replacement. Compare to control culture, culture with cyclic pressure oscillation could enhance cell expression level and reduce the ratio of glucose metabolized anaerobically to produce lactate. With four-step purification process, about 80 g u-PA(approximately 90% scu-PA) was recovered from approximately 2100 liters supernatant which contained approximately 135 g u-PA.

[Expression of prourokinase in different mammalian cells]

Comparison studies of recombinant prourokinase(pro-UK) in various host cells, and expression vectors were carried out. Expression levels of vectors constructed in this study in different cell lines were compared. Mammalian cells expressing pro-UK were established. The levels of pro-UK expression in recombinant Namalwa, Vero and Sp2/0 cells are 200, 12.5 and 50 IU/(10(6) cells 24 h). pro-UK purities separated by immunoaffinity chromatograph are above 90%. Immunoabsorbent assay showed the ratio of pro-UK in CHO cells is lower than that from Vero and Namalwa cells. This study provide new host cells for pro-UK production.

[Cloning of human G-CSF genomic gene and its expression in transgenic mice mammary gland]

Human genomic DNA was used as template of PCR. 1.5 kb G-CSF genomic DNA was obtained using PCR amplification method. Sequence analysis showed that genomic DNA sequence of human G-CSF was correct. The vector of mammary gland expression was constructed and contained whey acid protein (WAP) 5' control region directed human G-CSF genomic DNA. In order to produce transgenic mice, 1200 fertilized eggs were microninjected using WAP-G-CSF fragment. Two male transgenic mice were obtained and identified using PCR method and Southern analysis. Integration rate of human G-CSF gene was 2.37% in mice. Foreign gene could also be identified in F1 and F2 transgenic mice. Expression levels of human G-CSF in transgenic mouse milk were 120-250 ng/ml.

[Studies of foreign gene integeation during embryo early development]

There are still some problems in transgenic animals. Gene transfer, for example, reamins a difficult and costly task for animals, the vectors carrying the gene coding for the proteins of interest are of unpredictable efficiency. Therefore, it is important to identify foreign gene integration in genomose before transferring fertilized eggs to receptors, in order to increase efficiency of producing transgenic animal. In this paper, the construct that mice whey acid protein (WAP) gene promoter directs G-CSF gene was used to microinject fertilized eggs of mice. Fertilized eggs containing foreign gene were measured by using PCR method. The results showed that 100%, 77.7% and 44.4% retentions of foreign gene were achieved in 1, 2 and 8 cell-stage, respectively. Two part homologous recombination fragments were constructed and coinjected in to fertilized eggs of mice. PCR amplification fragment went beyond this homologous recombination area. If foreign gene could not integrate in to genomose, the fragment of PCR amplification could not be produced during embryo development. The results showed that the rationes of foreign gene integrated in to genomoes in 1, 2 and 8 cell-stage were 11.1%, 55.5% and 44.4%, respectively. This method might provide us a way to screen transgenic eggs when we use embryo section technique in farm animal.

[Serum beta 2-microglobulin and carcinoembryonic antigen in patients with bronchogenic carcinoma]

In patients with bronchogenic carcinoma of various types and stages, serum beta 2-microglobulin (beta 2-M) and carcinoembryonic antigen (CEA) were assayed simultaneously. The concentrations of serum beta 2-M and CEA were found to be statistically related to complete remission of the tumor (P less than 0.01). But it was also found that there was no correlation between the levels of beta 2-M and CEA (r = 0.0621). In follow-up, the CEA was found to be increasing incessantly as the disease progressed. For the level of serum beta 2-M, as the patients' condition got worse, it first rose, then dropped and became markedly lower before the patient died. The serum beta 2-M was often elevated 3-5 months earlier than CEA, and frequently resumed the normal level later than CEA after the carcinoma had a complete remission. With the progression of the bronchogenic carcinoma, elevation of beta 2-M was not necessarily a sign of poor prognosis. In contrast, with the serum beta 2-M markedly lowered after an initial elevation, the serum CEA became elevated, the prognosis was usually poor. The authors believe that, in patients with lung cancer, CEA produced from the lung cancer cells would give a level fluctuating with the size of the primary focus and the extent of the metastasis. But its positive rate is rather low. The serum beta 2-M is produced indirectly by certain immunologic function against bronchogenic carcinoma or its metabolites and not by the cancer cells directly. The positive rate of beta 2-M is high, so slightly is its false positive rate.(ABSTRACT TRUNCATED AT 250 WORDS)