An E-band multi-channel Doppler backscattering system on EAST

An E-band (60-90 GHz) multi-channel Doppler backscattering (DBS) system with X-mode polarization has been installed on the Experimental Advanced Superconducting Tokamak (EAST), which can measure the turbulence at five different radial locations simultaneously. This system can launch 31 fixed microwave frequencies in the range of 60-90 GHz with a 1 GHz interval into the plasma, and five probing signals are selected by employing a reference signal and multiple filters. During experiments, the frequency of the reference signal is tunable in the E-band, and the selected probing signals can be changed as needed without any other adjustments, which can be performed in one shot or between shots. Furthermore, the incident angle can be adjusted from -10° to 20°, and the wavenumber range is 4-25 cm-1 with a wavenumber resolution of Δk/k ≤ 0.35. Ray tracing simulations are employed to calculate the scattering locations and the perpendicular wavenumber. In this article, the hardware design, ray tracing, and initial results obtained from the EAST plasma will be presented.

Experimental Evidence of Intrinsic Current Generation by Turbulence in Stationary Tokamak Plasmas

High-β_{θe} (a ratio of the electron thermal pressure to the poloidal magnetic pressure) steady-state long-pulse plasmas with steep central electron temperature gradient are achieved in the Experimental Advanced Superconducting Tokamak. An intrinsic current is observed to be modulated by turbulence driven by the electron temperature gradient. This turbulent current is generated in the countercurrent direction and can reach a maximum ratio of 25% of the bootstrap current. Gyrokinetic simulations and experimental observations indicate that the turbulence is the electron temperature gradient mode (ETG). The dominant mechanism for the turbulent current generation is due to the divergence of ETG-driven residual flux of current. Good agreement has been found between experiments and theory for the critical value of the electron temperature gradient triggering ETG and for the level of the turbulent current. The maximum values of turbulent current and electron temperature gradient lead to the destabilization of an m/n=1/1 kink mode, which by counteraction reduces the turbulence level (m and n are the poloidal and toroidal mode number, respectively). These observations suggest that the self-regulation system including turbulence, turbulent current, and kink mode is a contributing mechanism for sustaining the steady-state long-pulse high-β_{θe} regime.

The cross-polarization scattering system for the magnetic fluctuation measurement in the Experimental Advanced Superconducting Tokamak

The cross-polarization scattering (CPS) system for magnetic fluctuation measurements in the Experimental Advanced Superconducting Tokamak (EAST) has been designed and installed. Different from the Doppler reflectometer (DR) system, the CPS system detects the perpendicular polarization of the electromagnetic wave induced by magnetic fluctuations B̃. The CPS system in the EAST has been developed from the existing Doppler reflectometer system, and they are integrated together for simultaneous measurement of magnetic and density fluctuations. Ray-tracing simulations are used to calculate the scattering locations and the wavenumber coverage of the magnetic fluctuation for CPS. In the experiments, the CPS and DR system data were different in Doppler shift, amplitude, and spectrum broadening. In this article, the hardware design, the ray tracing, and the preliminary results of the system in the EAST are presented.

Five-channel tunable W-band Doppler backscattering system in the experimental advanced superconducting tokamak

A 5-channel Doppler backscattering system has been designed and installed in the Experimental Advanced Superconducting Tokamak (EAST). Through an I/Q-type double sideband modulator and a frequency multiplier, an array of finely spaced (Δf = 400 MHz) frequencies that span 1.6 GHz has been created. The center of the array bandwidth is tunable within the range of 75-97.8 GHz, which covers most of the W band (75-110 GHz). The incident angle can be adjusted from -4° to 12°, and the wavenumber range is 4-15 cm^-1 with a wavenumber resolution of Δk/k ≤ 0.35. Ray tracing is used to calculate the scattering location and the scattering wavenumber. This article details the hardware design, the ray tracing, and the preliminary experimental results from EAST plasmas.

A novel, tunable, multimodal microwave system for microwave reflectometry system

Based on a new technique, a tunable, multi-channel system that covers the Q-band (33-55 GHz) is presented in this article. It has a potential use of the Doppler backscattering system diagnostic that can measure the turbulence radial correlation and the perpendicular velocity of turbulence by changing the incident angle. The system consists primarily of a double-sideband (DSB) modulation and a multiplier, which creates four probing frequencies. The probing frequency enables the simultaneous analysis of the density fluctuations and flows at four distinct radial regions in tokamak plasma. The amplitude of the probing frequency can be adjusted by the initial phase of the intermediate frequency (IF) input from the double-sideband, and the typical flatness is less than 10 dB. The system was tested in the lab with a rotating grating, and the results show that the system can operate in the frequency range of 33-55 GHz with a Q-band multitude and that the power of each channel can be adjusted by the phase of the IF input of DSB.

[Effects of metformin on papillary thyroid carcinoma in nude rats model]

Objective:To establish an subcutaneous xenotransplanted tumor model of papillary thyroid carcinoma (PTC) and investigate the role of metformin in apoptosis of PTC.Method:Model rats were randomly divided into four groups: control group, Met group and Met+DM group. The tumor volumes were recorded each week. Flow cytometry was used to detect the apoptosis rate of tumor. Immunohistochemistry was used to detect CyclinD1 and the cellular proliferative activity index PCNA and Ki-67.Result:Compared to the control group,there were a significant decrease in tumor volume and antitumor effect in Met and Met+DM groups. The apoptosis rate increased in Met and Met+DM groups. While compared with the control group, the expressions of PCNA,CyclinD1 and Ki-67 significantly decreased in Met and Met+DM groups. There was no difference between Met and Met+DM group.Conclusion:The effect of Metformin on inhibiting tumor growth were related with the imbalance of cell proliferation and apoptosis.

A novel approach to estimating the Doppler shift frequency from quadrature mixer output

Doppler backscattering systems (DBSs) have been widely used in magnetic confinement fusion devices to measure the density fluctuations and propagation velocity of turbulence. However, the received signals of a DBS usually include both zero-order reflection and backscattering components, which results in interference in calculating the Doppler shift frequency from the backscattering components. A novel method is introduced here for estimating the Doppler shift frequency by separating the zero-order reflection and backscattering components using the cross-phase spectrum between the I-signal and Q-signal from a quadrature mixer, based on the difference in symmetrical characteristics between the zero-order reflection and backscattering signal spectra. It is proven that this method is more effective than traditional approaches, such as multiple signal classification and fast Fourier transformation, for extracting Doppler shift information.

An eight-channel Doppler backscattering system in the experimental advanced superconducting tokamak

Doppler backscattering system can measure the perpendicular velocity and fluctuation amplitude of the density turbulence with intermediate wavenumber. An eight-channel Doppler backscattering system has been installed in the Experimental Advanced Superconducting Tokamak (EAST), which can probe eight different radial locations simultaneously by launching eight fixed frequencies (55, 57.5, 60, 62.5, 67.5, 70, 72.5, 75 GHz) into plasma. The quasi-optical system consists of circular corrugated waveguide transmission, a fixed parabolic mirror, and a rotatable parabolic mirror which are integrated with quasi-optics front-end of the profile reflectometer inside the vacuum vessel. The incidence angle can be chosen from 5° to 12°, and the wavenumber range is 2-15/cm with the wavenumber resolution Δk/k≤0.21. Ray tracing simulations are used to calculate the scattering locations and the perpendicular wavenumber. The dynamic range of this new eight-channel Doppler backscattering system can be as large as 40 dB in the EAST. In this article, the hardware design, the ray tracing, and the preliminary experimental results in the EAST will be presented.

[Metformin induced apoptosis of papillary thyroid carcinoma BCPAP cells]

Objective:To investigate the role of metformin in inducing apoptosis of papillary thyroid carcinoma BCPAP cells. Method:Using MTT methods to detect effects of metformin on cell proliferation of BCPAP in different concentrations (0 mmol/L, 1 mmol/L, 5 mmol/L, 10 mmol/L, 20 mmol/L) and time course (0 h, 4 h, 8 h, 16 h, 24 h, 48 h). The experiment was divided into four groups: Con, Met, Met+Sal and Met+DM, flow cytometry to detect the rate of apoptosis of BCPAP. Then detect the protein expressions of CHOP, GRP78 and Caspase-12 of 4 groups by Western blot. Result:Compared with the experimental control group, the percentage of cell proliferation index significantly decreased in metformin (0-20 mmol/L and 0-48 h) treatment group. Compared with the experimental control group, the percentage of apoptosis cells significantly increased in metformin treatment group. Compared with the control group, the protein expressions of GRP78, CHOP and Caspase-12 were significantly increased in Met group; While compared with the Met group, the protein expressions of GRP78, CHOP and Caspase-12 were significantly inhibited in the Met+Sal group. Conclusion:Metformin can induced availably BCPAP cell apoptosis by activating endoplasmic reticulum stress mechanism.

Influence of lithium coating on the optics of Doppler backscatter system

This paper presents the first investigation of the effect of lithium coating on the optics of Doppler backscattering. A liquid lithium limiter has been applied in the Experimental Advanced Superconducting Tokamak (EAST), and a Doppler backscattering has been installed in the EAST. A parabolic mirror and a flat mirror located in the vacuum vessel are polluted by lithium. An identical optical system of the Doppler backscattering is set up in laboratory. The power distributions of the emission beam after the two mirrors with and without lithium coating (cleaned before and after), are measured at three different distances under four incident frequencies. The results demonstrate that the influence of the lithium coating on the power distributions are very slight, and the Doppler backscattering can work normally under the dosage of lithium during the 2014 EAST campaign.

Microwave Doppler reflectometer system in the Experimental Advanced Superconducting Tokamak

A Doppler reflectometer system has recently been installed in the Experimental Advanced Superconducting (EAST) Tokamak. It includes two separated systems, one for Q-band (33-50 GHz) and the other for V-band (50-75 GHz). The optical system consists of a flat mirror and a parabolic mirror which are optimized to improve the spectral resolution. A synthesizer is used as the source and a 20 MHz single band frequency modulator is used to get a differential frequency for heterodyne detection. Ray tracing simulations are used to calculate the scattering location and the perpendicular wave number. In EAST last experimental campaign, the Doppler shifted signals have been obtained and the radial profiles of the perpendicular propagation velocity during L-mode and H-mode are calculated.

Dynamics of low-intermediate-high-confinement transitions in toroidal plasmas

The dynamic features of the low-intermediate-high-(L-I-H) confinement transitions on HL-2A tokamak are presented. Here we report the discovery of two types of limit cycles (dubbed type-Y and type-J), which show opposite temporal ordering between the radial electric field and turbulence intensity. In type-Y, which appears first after an L-I transition, the turbulence grows first, followed by the localized electric field. In contrast, the electric field leads type-J. The turbulence-induced zonal flow and pressure-gradient-induced drift play essential roles in the two types of limit cycles, respectively. The condition of transition between types-Y and -J is studied in terms of the normalized radial electric field. An I-H transition is demonstrated to occur only from type-J.

First evidence of the role of zonal flows for the L-H transition at marginal input power in the EAST tokamak

A quasiperiodic Er oscillation at a frequency of <4 kHz, much lower than the geodesic-acoustic-mode frequency, with a modulation in edge turbulence preceding and following the low-to-high (L-H) confinement mode transition, has been observed for the first time in the EAST tokamak, using two toroidally separated reciprocating probes. Just prior to the L-H transition, the Er oscillation often evolves into intermittent negative Er spikes. The low-frequency Er oscillation, as well as the Er spikes, is strongly correlated with the turbulence-driven Reynolds stress, thus providing first evidence of the role of the zonal flows in the L-H transition at marginal input power. These new findings not only shed light on the underlying physics mechanism for the L-H transition, but also have significant implications for ITER operations close to the L-H transition threshold power.

Characterizations of low-frequency zonal flow in the edge plasma of the HL-2A tokamak

A low-frequency (<4 kHz), poloidally and toroidally symmetrical potential structure that peaks near zero frequency is observed in the edge plasma of the HL-2A tokamak. The axisymmetry structure exhibits a radial coherence length less than 1 cm. These characteristics are consistent with the theoretically predicted low-frequency zonal flows (LFZF). The radial wave-number frequency spectra of the LFZF show that the LFZF packets propagate both outwards and inwards. The geodesic acoustic mode (GAM) is found to coexist with the LFZF, and the LFZF is found to modulate the GAM and ambient turbulence with in-phase and antiphase relations, respectively, through an envelope analysis.

Toroidal symmetry of the geodesic acoustic mode zonal flow in a tokamak plasma

The toroidal symmetry of the geodesic acoustic mode (GAM) zonal flows is identified with toroidally distributed three step Langmuir probes at the edge of the HuanLiuqi-2A (commonly referred to as HL-2A) tokamak plasmas for the first time. High coherence of both the GAM and the ambient turbulence for the toroidally displaced measurements along a magnetic field line is observed, in contrast with the high coherence of the GAM but low coherence of the ambient turbulence when the toroidally displaced measurements are not along the same field line. The radial and poloidal features of the flows are also simultaneously determined. The nonlinear three wave coupling between the high frequency turbulent fluctuations and the flows is demonstrated to be a plausible formation mechanism of the flows.

Construction of stabilized proteins by combinatorial consensus mutagenesis

We constructed stabilized variants of beta-lactamase (BLA) from Enterobacter cloacae by combinatorial recruitment of consensus mutations. By aligning the sequences of 38 BLA homologs, we identified 29 positions where the E.cloacae gene differs from the consensus sequence of lactamases and constructed combinatorial libraries using mixtures of mutagenic oligonucleotides encompassing all 29 positions. Screening of 90 random isolates from these libraries identified 15 variants with significantly increased thermostability. The stability of these isolates suggest that all tested mutations make additive contributions to protein stability. A statistical analysis of sequence and stability data identified 11 mutations that made stabilizing contributions and eight mutations that destabilized the protein. A second-generation library recombining these 11 stabilizing mutations led to the identification of BLA variants that showed further stabilization. The most stable variant had a mid-point of thermal denaturation (Tm) that was 9.1 degrees C higher than the starting molecule and contained eight consensus mutations. Incubation of three stabilized BLA variants with several proteases showed that all tested isolates have significantly increased resistance to proteolysis. Our data demonstrate that combinatorial consensus mutagenesis (CCM) allows the rapid generation of protein variants with improved thermal and proteolytic stability.

Central norepinephrine pathways are involved in cardiovascular response to intracerebroventricular substance P

AIM

To study the role of norepinephrine system in the cardiovascular response to intracerebroventricular substance P (SP) in rabbit.

METHODS

SP was given intracerebroventricularly in anesthetized rabbits pretreated with the catecholaminergic neurotoxin, 6-hydroxydopamine (6-OHDA). The density and affinity of SP receptors on synaptosomal membranes of the hypothalamus and the ventral medulla of rabbits were determined by [125I]SP receptor assay. Arterial blood pressure and heart rate were recorded.

RESULTS

Intracerebroventricular (icv) pretreatment of rabbits with 6-OHDA, reduced norepinephrine in the hypothalamus (by 86.7 %) and in the ventral medulla (by 77.0 %) respectively. The pressor response and tachycardia of these rabbits to icv SP (3.55 nmol . kg-1) were attenuated. The density and the affinity of SP receptors in the hypothalamus and the ventral medulla of 6-OHDA-lesioned rabbits were decreased. The Bmax (pmol . g-1 protein) of SP receptors in hypothalamus and the ventral medulla are 108 +/- 5, 35.9 +/- 2.2 in control group, and 42 +/- 18, 20 +/- 5 in 6-OHDA-lesioned rabbits, respectively. Kd (nmol . L-1) of SP receptors in the two regions are 0.015 +/- 0.004, 0.014 +/- 0.006 in control group and 0.029 +/- 0.001, 0.015 +/- 0.003 in 6-OHDA group. There is a significant difference of Bmax (P < 0.01) and Kd (P < 0.01, P < 0.05) in both regions between 6-OHDA groups and control groups.

CONCLUSION

The results suggested that central norepinephrine pathways are involved in the cardiovascular response to icv SP.

Rapid in vivo evolution of a beta-lactamase using phagemids

RNA viruses are capable of undergoing extremely rapid evolution due to their high rates of reproduction, small genome size, and a high frequency of spontaneous mutagenesis. Here we demonstrate that a virus-like, evolutionary state can be created by propagating a phagemid population in a hypermutator strain of Escherichia coli in the presence of a helper phage. This enables one to subject individual phagemid-encoded genes to rapid in vivo evolution. We applied this approach to TEM-1 beta-lactamase which confers resistance to 0.05 mg/L of the antibiotic cefotaxime. After 3 weeks of in vivo evolution we were able to isolate a double mutant, E104K/G238S, of the enzyme which confers a 500-fold increased level of resistance to cefotaxime compared to the starting enzyme. In two independent experiments we obtained a triple mutant, E104K/G238S/T263M, which confers a 1000-fold increase in resistance compared to the wild type enzyme. The same three mutations have been previously observed in TEM-4 beta-lactamase which was discovered in a highly cefotaxime-resistant clinical isolate. The probability of randomly obtaining a beta-lactamase carrying three identical point mutations is less than 10(-10). This indicates that phagemid evolution can rapidly reproduce evolution occurring in nature.