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A gyrotron traveling-wave amplifier (gyro-TWA) with a distributed-loss structure can achieve high gain over a broad bandwidth. In this study, a low-voltage, low-current subterahertz gyro-TWA with medium power (∼10 W) over a broad-frequency range (∼10 GHz) is designed. The excessive length of the copper section in this gyro-TWA leads to reflective oscillations and absolute instabilities. Reflective oscillations can be suppressed for a gyro-TWA with a high lossy-section resistivity and a short copper section. Absolute instabilities, conversely, can be suppressed for a gyro-TWA with a long lossy section and high lossy-section resistivity. The proposed gyro-TWA has a high lossy-section resistivity, a long lossy section, and a short copper section, which not only avoids mode competition but also achieves the desired characteristics of a high gain and broad-frequency range. For a 12 kV, 0.3 A electron beam, the frequency range of the 250 GHz 10 W level gyro-TWA with a distributed-loss structure, is ∼10 GHz when the input power is between 1 and 10 mW. [ABSTRACT FROM AUTHOR]

Gyrotrons operating at low voltage are highly attractive for subterahertz applications because such an operation can greatly reduce the size and cost of gyrotron systems. Among the oscillator versions of gyrotrons, the gyrotron backward-wave oscillator (gyro-BWO) features continuous frequency tuning in a broadband. This study investigates the characteristics of the beam-wave interaction in a low-voltage gyro-BWO in the subterahertz wave range. Operation at lower voltages has the advantage of a broader frequency tuning range and the suppression of negative $k_{z}$ competing modes. The phenomenon of a sharp increase in the start-oscillation current near the lower limit of the operating voltage is investigated. In addition to the linear characteristics, the dependence of the efficiency and tuning bandwidth on voltage is analyzed. The potential performance of a low-voltage gyro-BWO is predicted using the existing beam parameters: beam voltage of 2 kV, beam current of 0.2 A with a velocity ratio of 1.0, and axial velocity spread of 20%. Although the gyro-BWO operating at 2 kV exhibits the problem of low efficiency (an efficiency of 5.6%), it has a broad frequency tuning range of 3.0 GHz. The efficiency can be enhanced to 15% (a peak power of 60 W) by tapering the waveguide radius. Possible competing modes in low-voltage operation are considered and a stability analysis reveals stable operation. [ABSTRACT FROM AUTHOR]

Theoretical investigations of InGaN tandem solar cells with intermediate bands (IBs) have been conducted through calculating the diode equation taking into account the radiative and nonradiative recombination currents. The calculated maximum efficiencies of the double-junction cell with one IB in each subcell are 57.85% and 68.37% under AM1.5G one-sun and 46000-sun illuminations, respectively. It has also been observed that the combined device with the top-cell bandgaps of 2.9-3.4 eV (2.6-3.4 eV for full concentration) may have an opportunity to realize the application of over 50% efficiency. We suggest that the optimized width of the IB layer be designed in the range of 1-6 μm if its absorption coefficient is 104-105 cm-1 in the IB region. [ABSTRACT FROM AUTHOR]

Mode competition is a severe problem in the development of a high-power gyrotron backward-wave oscillator (gyro-BWO) in terahertz (THz) region. To improve the stability of this device, this paper investigates the possibility of using a tapered coaxial waveguide as the interaction structure of a 0.3-THz gyro-BWO. The inner cylinder rarefies the mode density near the operating mode. Moreover, tapering the wall of the outer cylinder suppresses almost all the competing modes and shifts the optimum magnetic tuning range of the operating mode under stable operating conditions. The gyro-BWO is predicted to stably generate a peak power of 17.2 kW with 11.5% efficiency at 0.307 THz, and a continuous tuning bandwidth of 3.4 GHz (\approx1.1\%) for a 30-kV, 5-A electron beam with $\alpha=1.0$ and an axial velocity spread of 5%. Compared with the uniform case, the tapered coaxial interaction waveguide enhances both the stability and the frequency tunability of the THz gyro-BWO. [ABSTRACT FROM AUTHOR]

The gyrotron traveling-wave-tube (gyro-TWT) amplifier is a high-power broad-band millimeter-wave amplifier. Its operation at a high harmonic number is of practical importance because the required magnetic field strength can be reduced by a factor of the harmonic number. Although hollow circular waveguides have typically been used as the interaction structure in harmonic gyro-TWTs, spurious oscillations limit their performance. This study investigates the possibility of using coaxial waveguides as the interaction structure in a second-harmonic gyro-TWT. Stability is achieved by applying distributed losses on the outer and inner walls. Simulation results indicate that the distributed losses on the inner wall can suppress specific oscillating modes without deteriorating the performance of the amplifying mode. Under stable operating conditions, simulations indicate that the second-harmonic coaxial gyro-TWT generates a peak power of 293 kW in the Ka-band with 21% efficiency, a saturated gain of 42 dB, and a bandwidth of 1.31 GHz (\approx 4.1\%) for a 70-kV 20-A electron beam with an \alpha = 1.0 and an axial velocity spread of 5%. [ABSTRACT FROM PUBLISHER]

A dual-band amplifier can reduce the size, cost, and weight of a transmitter in dual-band radar and communication systems. This study proposes and theoretically investigates a gyrotron traveling-wave tube (gyro-TWT) amplifier capable of dual-band operation. Possible oscillations in the coaxial interaction waveguide are stabilized by the lossy inner cylinder. Under stable operating conditions, the gyro-TWT is predicted to provide a peak power of 375 kW with 71 dB saturated gain and 3.8 GHz bandwidth in the Ka-band and a peak power of 150 kW with 35 dB saturated gain and 1.7 GHz bandwidth in the V-band. [ABSTRACT FROM AUTHOR]

Summary BAX protein plays a key role in the mitochondria-mediated apoptosis. However, it remains unclear by what mechanism BAX is triggered to initiate apoptosis. Here, we reveal the mechanism using electron spin resonance (ESR) techniques. An inactive BAX monomer was found to exhibit conformational heterogeneity and exist at equilibrium in two conformations, one of which has never been reported. We show that upon apoptotic stimulus by BH3-only peptides, BAX can be induced to convert into either a ligand-bound monomer or an oligomer through a conformational selection mechanism. The kinetics of reaction is studied by means of time-resolved ESR, allowing a direct in situ observation for the transformation of BAX from the native to the bound states. In vitro mitochondrial assays provide further discrimination between the proposed BAX states, thereby revealing a population-shift allosteric mechanism in the process. BAX’s apoptotic function is shown to critically depend on excursions between different structural conformations. [ABSTRACT FROM AUTHOR]

BAX activation is a crucial step for commitment to apoptosis. Several activators, such as BimBH3-based therapeutic peptides and cleaved Bid (cBid) protein, can trigger BAX-mediated apoptosis, but it is unclear whether they proceed through the same pathway. Here we utilize PEGylation-based approach, which is shown to efficiently shield individual binding grooves in BAX from activators, to investigate and reveal that the activators take different routes to induce BAX-mediated apoptosis. Various spectroscopic/biochemical tools, including electron spin resonance, circular dichroism, fluorescence recovery after photobleaching, and label-transfer assay, were employed to reveal details in the processes. We observe a key mutant BAX 164-PEG that acts differently in response to cBid and BimBH3 stimuli. While BimBH3 directly interacts with the trigger groove (TG) to induce the conformational changes in BAX that includes the release of α9 from the canonical groove (CG) and oligomerization, cBid engages with CG and works with mitochondrial lipids to fully activate BAX. PEGylation-based approach is proven useful to shield individual binding grooves of BAX from apoptotic stimuli. Groove engagement in CG of BAX is required for a full cBid-induced BAX activation. This study has identified differences in the pathways involved during the initiation of BAX activation by full-length cBid protein versus synthetic BimBH3-based peptides. Our finding is potentially valuable for therapeutic application as the pore-forming activity of 164-PEG is independent from the cBid-mediated apoptotic pathways, but can be administrated by the synthetic short peptides. Unlabelled Image • A full BAX activation for MOMP proceeds with two steps essentially. • Accessibility of trigger groove of BAX is required for initiation of activation. • BimBH3 peptide and cBid take different routes to activate BAX. • Cleaved Bid interacts with the canonical groove to promote BAX activation. • Accessibility of canonical groove is not strictly required for BAX activation. [ABSTRACT FROM AUTHOR]

Brown rice was exposed to low-pressure plasma ranging from 1 to 3 kV for 10 min. Treatment of brown rice in low-pressure plasma increases the germination percentage, seedling length, and water uptake in laboratory germination tests. Of the various treatments, 3-kV plasma exposure for 10 min yielded the best results. In germinating brown rice, α-amylase activity was significantly higher in treated groups than in controls. The higher enzyme activity in plasma-treated brown rice likely triggers the rapid germination and earlier vigor of the seedlings. Low-pressure plasma also increased gamma-aminobutyric acid (GABA) levels from ∼19 to ∼28 mg/100 g. In addition, a marked increase in the antioxidant activity of brown rice was observed with plasma treatments compared to controls. The main finding of this study indicates that low-pressure plasma is effective at enhancing the growth and GABA accumulation of germinated brown rice, which can supply high nutrition to consumer. [ABSTRACT FROM AUTHOR]

Summary Proapoptotic BAX protein is largely cytosolic in healthy cells, but it oligomerizes and translocates to mitochondria upon receiving apoptotic stimuli. A long-standing challenge has been the inability to capture any structural information beyond the onset of activation. Here, we present solution structures of an activated BAX oligomer by means of spectroscopic and scattering methods, providing details about the monomer-monomer interfaces in the oligomer and how the oligomer is assembled from homodimers. We show that this soluble oligomer undergoes a direct conversion into membrane-inserted oligomer, which has the ability of inducing apoptosis and structurally resembles a membrane-embedded oligomer formed from BAX monomers in lipid environment. Structural differences between the soluble and the membrane-inserted oligomers are manifested in the C-terminal helices. Our data suggest an alternative pathway of apoptosis in which BAX oligomer formation occurs prior to membrane insertion. [ABSTRACT FROM AUTHOR]