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We report experimental results on the microfabrication of three types of folded waveguide circuits with a high aspect ratio by using a high-energy X-ray LIGA technique. A W-band folded waveguide with a total of 80 periods was designed for a traveling-wave-tube (TWT) amplifier operating at 90 GHz–100 GHz. The measured return loss and insertion loss of the W-band fabricated circuit were–10 dB and 0.42 dB/cm, respectively. A G-band circuit showed a higher insertion loss of 1.57 dB/cm. An additional circuit fabrication for a 850-GHz folded waveguide TWT was also successfully carried out. The broad-wall angle measured with respect to the narrow wall of the rectangular waveguide was very close to 90◦, indicating an excellent resolution compared to that of other microfabrication techniques, such as deep reactive ion etching (DRIE) and ultraviolet (UV) lithography, electroplating, and polymer replication (LIGA).

Although immune checkpoint inhibitors have emerged as a breakthrough in cancer therapy, a monotherapy approach is not sufficient. Here, we report an immune checkpoint inhibitor-modified nanoparticle for an in situ-assembled tumor vaccine that can activate immune systems in the tumor microenvironment and prevent the long-term recurrence of tumors. Adjuvant-loaded nanoparticles were prepared by entrapping imiquimod (IQ) in photoresponsive polydopamine nanoparticles (IQ/PNs). The surfaces of IQ/PNs were then modified with anti-PDL1 antibody (PDL1Ab-IQ/PNs) for in situ assembly with inactivated tumor cells and immune checkpoint blocking of PDL1 (programmed cell death 1 ligand 1). The presence of anti-PDL1 antibodies on IQ/PNs increased the binding of nanoparticles to CT26 cancer cells overexpressing PDL1. Subsequent near-infrared (NIR) irradiation induced a greater photothermal anticancer effect against cells treated with PDL1Ab-IQ/PNs than cells treated with plain PNs or unmodified IQ/PNs. To mimic the tumor microenvironment, we cocultured bone marrow-derived dendritic cells with CT26 cells treated with various nanoparticle formulations and NIR irradiated. This coculture study revealed that NIR-inactivated, PDL1Ab-IQ/PN-bound CT26 cells induced maturation of dendritic cells to the greatest extent. Following a single intravenous administration of different nanoparticle formulations in CT26 tumor-bearing mice, PDL1Ab-IQ/PNs showed greater tumor tissue accumulation than unmodified nanoparticles. Subsequent NIR irradiation of mice treated with PDL1Ab-IQ/PNs resulted in tumor ablation. In addition to primary tumor ablation, PDL1Ab-IQ/PNs completely prevented the growth of a secondarily challenged CT26 tumor at a distant site, producing 100% survival for up to 150 days. A long-term protection study revealed that treatment with PDL1Ab-IQ/PNs followed by NIR irradiation inhibited the growth of distant, secondarily challenged CT26 tumors 150 days after the first tumor inoculation. Moreover, increased infiltration of T cells was observed in tumor tissues treated with PDL1Ab-IQ/PNs and NIR-irradiated, and T cells isolated from splenocytes of mice in which tumor recurrence was prevented showed active killing of CT26 cells. These results suggest that PDL1Ab-IQ/PNs in conjunction with NIR irradiation induce a potent, in situ-assembled, all-in-one tumor vaccine with adjuvant-containing nanoparticle-bound, inactivated tumor cells. Such in situ nanoadjuvant-assembled tumor vaccines can be further developed for long-term prevention of tumor recurrence without the need for chemotherapy.

Microwave (MW) radiation is increasingly being used for several biological applications. Many investigations have focused on understanding the potential influences of pulsed MW irradiation on biological solutions. The current study aimed to investigate the effects of 3.5 GHz pulsed MW radiation-irradiated liquid solutions on the survival of human cancer and normal cells. Different physiological solutions such as phosphate buffer saline, deionized water, and Dulbecco’s modified Eagle medium (DMEM) for cell culture growth were irradiated with pulsed MW radiation (45 shots with the energy of 1 mJ/shot). We then evaluated physiological effects such as cell viability, metabolic activity, mitochondrial membrane potential, cell cycle, and cell death in cells treated with MW-irradiated biological solutions. As MW irradiation with power density ~ 12 kW/cm2 mainly induces reactive nitrogen oxygen species in deionized water, it altered the cell cycle, membrane potential, and cell death rates in U373MG cells due to its high electric field ~ 11 kV/cm in water. Interestingly, MW-irradiated cell culture medium and phosphate-buffered saline did not alter the cellular viability and metabolic energy of cancer and normal cells without affecting the expression of genes responsible for cell death. Taken together, MW-irradiated water can alter cellular physiology noticeably, whereas irradiated media and buffered saline solutions induce negligible or irrelevant changes that do not affect cellular health.

Cancer immunotherapy takes advantage of immune system to fight against cancer. Current clinical immunotherapies are based on the administration of immune checkpoint inhibitors or immune modulators to reverse the immune suppression. Although robust and long-term tumor suppression is induced in “certain treated population”, single immunotherapy still suffers from limited efficacy in clinic. Combination with nanomedicine would be one of major strategies that can widen the effective patient populations and reduce side effects. The basis in combining nanomedicine and immunotherapy stems from the close relationship of tumor and immune system. Depending on the therapeutic cargo, nanocarriers can not only facilitate stronger innate or adaptive immunity but also reverse of immunosuppression. In the other hand, nanotechnology can potentiate the efficacy of immunotherapy by enhancing the delivery, retention and narrow the toxicity of immunomodulators. The strategies and rationales of nanocarrier design in the context of cancer immunotherapy are discussed in this review.

Although various oral pathogens are inactivated by non-thermal atmospheric pressure plasma (NTAPP), the in vivo effects of NTAPP are poorly understood. The first aim of this study was to examine the antibacterial activity of microwave-pulsed NTAPP against Staphylococcus aureus in artificial saliva to mimic oral environmental conditions. The second aim was to determine the influence of microwave-pulsed NTAPP on human gingival fibroblasts (HGFs). The microwave-pulsed NTAPP reduced bacterial viability (as measured by colony forming units [CFU]) to a greater extent in artificial saliva than in saline. Extending the post-treatment incubation time increased bacterial inactivation in artificial saliva compared to saline. HGFs viability was unaffected by microwave-pulsed NTAPP for bacterial inactivation. Rather, HGFs proliferation increased after a 5-min microwave-pulsed NTAPP. Less tumor necrosis factor alpha was released by microwave-pulsed NTAPP-treated HGFs stimulated with lipopolysaccharide (LPS) than by untreated, LPS-stimulated HGFs; thus, plasma appeared to suppress the inflammatory response. Our study suggests that microwave-pulsed NTAPP may have stronger in vivo antibacterial activity than in vitro activity, and that microwave-pulsed NTAPP may have the additional advantage of suppressing gingival inflammatory responses.

Nucleic acid-based adjuvants have recently emerged as promising candidates for use in cancer vaccines to induce tumor-suppressing immune cells. In this study, we tested whether complexation of a nucleic acid-based adjuvant with chitosan (CTS) modulates immune adjuvant functions. As a nucleic acid-based adjuvant, we used toll-like receptor 3-recognizing RNA adjuvant (RA). Negatively charged RA formed nanoscale polyplexes with cationic CTS that possessed positive zeta potentials. RA/CTS polyplexes exerted dendritic cell (DC)-maturation effects without causing significant DC toxicity. This DC-maturation effect was CTS molecular weight dependent, with RA/CTS polyplexes with a CTS molecular weight of 340 kDa (RA/CTS 340K) producing the greatest effect. Subcutaneous injection of RA/CTS 340K polyplexes with the model tumor antigen ovalbumin exerted a preventive effect against challenge by ovalbumin-expressing tumor cells. It also provided greater inhibitory effects against a second challenge with the same tumor cells compared with other treatments. These protective effects of subcutaneous RA/CTS polyplex treatment were associated with the highest tumor antigen-specific humoral and cellular immune responses after tumor challenge, and with the greatest infiltration of CD4 helper T cell and CD8 T cell into the tumor tissues. Mice vaccinated with ovalbumin and RA/CTS polyplexes showed complete survival, even after repeated challenge with tumor cells. Our results suggest the potential of RA/CTS polyplexes as effective nanoadjuvants in the design of tumor vaccines and cancer immunotherapy.

A virtual cathode oscillator (vircator) is a special type of oscillator capable of generating high-power microwaves. We studied an axially extracted vircator by installing a cone-shaped reflector in our pulsed power device, “Chundoong” and numerically studied by using a three-dimensional particle-in-cell simulation, MAGIC. In the simulation, we varied the inner diameter of the reflector between 9 cm and 17 cm; a diameter of 13 cm showed the maximum power enhancement measured at the end of the drift tube position. The dominant oscillating frequencies without and with reflector were determined to be 3.42 GHz and 3.37 GHz, respectively, in the simulation and 3.40 GHz and 3.31 GHz, respectively, in the experiment. The numerically predicted frequencies showed good agreement with those observed during the experiment. The microwave power generated from the conventional axial vircator was 571 MW with the efficiency approximately 20%; which is increased by the interference up to 835 MW with the efficiency of 29.4% with reflector. The microwave power increased to 46% with the reflector. The microwave emission mode from the axial vircator was TM01 with and without reflector, based on the vector electric and magnetic fields observed during the simulation. The presented reflector increases the microwave power significantly. This reflector may possibly be used to increase the microwave power by the interference to increase efficiency of vircator sources. Keywords: Vircator, Cone-shaped reflector, Pulsed power, Chundoong, Particle-in-cell simulation, MAGIC, Power enhancement, Power efficiency

This paper describes a study and experimental demonstration on a magnetron operating at 2.45 GHz. We checked the characteristics of the 1 kW magnetron. There were two noise sources of magnetron at frequencies of 0.5 Hz and 75 kHz. In order to suppress these noises, we used an external injection locking method. Measurement results showed that the frequency noise suppression was down up to 30 dBc and the phase fluctuation is reduced to 4 degrees when injection input power was 7 W. Power combining experiments were performed using two identical magnetrons. An initial result showed an output power of 2 kW, corresponding to combining efficiency $\pmb{ > 93\%}$ .

Experiments on a 14-vane, double-strapped magnetron oscillator were performed to demonstrate high-power, high-efficiency coherent radiation at 5.8 GHz. The double-strapped magnetron was designed by using the Buneman-Hatree resonance condition, electromagnetic simulations and non-linear three-dimensional particle-in-cell (PIC) simulations. Experiments showed an oscillation output power of 5.3 kW at 5.79 GHz, corresponding to a DC-RF conversion efficiency of 57%. The cathode voltage was 9.2 kV, the collected anode current was 1 A, and the external magnetic field is 7.5 kG. Experimental results for the RF power, oscillation frequency, and efficiency were in good agreement with the corresponding values from non-linear three-dimensional PIC simulations.

This paper describes a design study and experimental demonstration on a cavity-type power combiner producing 80 kW at 464 MHz. The power combiner consists of (1) a 40-way equal phase/amplitude power divider, (2) a cavity-type power combiner, and (3) 40 LDMOS power amplifier modules. The power divider produces equal power and phase through a Ill-way radial power divider and 3-dB Wilkinson dividers. The power combiner is a cylindrical cavity resonating at TM010 mode with 40 input ports. The combined power is extracted through 6-1/8' coaxial transmission line. Measured results of the 40-way power combiner show an output power of 80 kW and combining efficiency of $> 95{\%}$ , which is in a good agreement with HFSS simulation results.

RF design and network analyzer tests of broadband, amplitude-balanced coaxial hybrid junctions are presented. We have designed two 3 dB hybrid splitters with 9 and 12 in. coaxial transmission lines applicable to ITER ICRF for load-resilient operations using ANSYS HFSS. Amplitude-balanced broadband responses were obtained with the combination of impedance reductions of longitudinal and transverse branches in unequal proportion, length change of 50 Ω lines and diameter change of high impedance lines connected transversely to the T-section of the hybrid splitter, respectively. We have fabricated and RF tested the 9 in. coaxial hybrid coupler. We obtained an excellent coupling flatness of −3.2 ± 0.2 dB, phase difference of 4 degrees and return loss of 16 dB in 40–55 MHz. The measured data of 9 in. hybrid splitter is highly consistent with HFSS simulations. We found that the proposed 3 dB hybrid splitter can be tunable with amplitude-balanced, broadband response by changing dielectric insulators to keep the inner and outer conductors of coaxial line apart. The proposed 3 dB hybrid splitter can be utilized for load-resilient operations in a wide range of antenna load variations due to mode transitions or edge localized modes (ELMs) in fusion plasmas.

A Ku-band gyrotron traveling-wave-tube (gyro-TWT) amplifier was investigated. To obtain a wide operating bandwidth, we used a two-stage tapered rectangular waveguide interaction circuit. An electron beam of 27 keV and 3.56 A was produced from a double-anode magnetron-injection-gun (MIG). The measured frequency bandwidth over 10 dB gain in the linear operation region was found to be 18%. The gyro-TWT’s saturated output power was 14.9 kW at 14.4 GHz, corresponding to a saturated output power gain of 27.4 dB and an efficiency of 15.5%. The measured experimental results were in agreement with those of non-linear numerical simulations.

A double-anode magnetron-injection gun (MIG) was designed. The MIG is for a W-band 10-kW gyrotron. Analytic equations based on adiabatic theory and angular momentum conservation were used to examine the initial design parameters such as the cathode angle, and the radius of the beam emitting surface. The MIG’s performances were predicted by using an electron trajectory code, the EGUN code. The beam spread of the axial velocity, Δvz/vz, obtained from the EGUN code was observed to be 1.34% at α = 1.3. The cathode edge emission and the thermal effect were modeled. The cathode edge emission was found to have a major effect on the velocity spread. The electron beam’s quality was significantly improved by affixing non-emissive cylinders to the cathode.

The biochemistry and microbial ecology of 2 similar types of watery (mul) kimchi, containing sliced and unsliced radish and vegetables (nabak and dongchimi, respectively), were investigated. Samples from kimchi were fermented at 4, 10, and 20 °C were analyzed by plating on differential and selective media, high-performance liquid chromatography, and high-throughput DNA sequencing of 16S rDNA. Nabak kimchi showed similar trends as dongchimi, with increasing lactic and acetic acids and decreasing pH for each temperature, but differences in microbiota were apparent. Interestingly, bacteria from the Proteobacterium phylum, including Enterobacteriaceae, decreased more rapidly during fermentation at 4 °C in nabak cabbage fermentations compared with dongchimi. Although changes for Proteobacterium and Enterobacteriaceae populations were similar during fermentation at 10 and 20 °C, the homolactic stage of fermentation did not develop for the 4 and 10 °C samples of both nabak and dongchimi during the experiment. These data show the differences in biochemistry and microbial ecology that can result from preparation method and fermentation conditions of the kimchi, which may impact safety (Enterobacteriaceae populations may include pathogenic bacteria) and quality (homolactic fermentation can be undesirable, if too much acid is produced) of the product. In addition, the data also illustrate the need for improved methods for identifying and differentiating closely related lactic acid bacteria species using high-throughput sequencing methods.

Sensory characteristics and chemical properties of 9 commercial dongchimi (Korean watery radish kimchi) liquid varieties were investigated using sensory descriptive analysis and instrumental analyses. Dongchimi was analyzed for pH, titratable acidity, soluble solids, salinity, organic acids, sugars, ethanol, and amino acids. Arginine, glutamic acid, and proline were the key amino acids. Lactic acid was the main organic acid in mature dongchimi. Based on sensory descriptive analysis, 4 appearances, 10 odors, 5 flavor/taste, and 3 mouthfeel sensory attributes were developed. Descriptive sensory and instrumental results showed that a white hue was associated with garlic, leek, and chili odors, glutamic acid, acetic acid, lactic acid, ethanol, and mannitol. Samples with a yellow hue were associated with turbidity, moldy and yeast odors, salty taste, fructose, glucose, and malic acid.

Plasma-jet systems and plasma devices of dielectric barrier discharge (DBD) are introduced for biomedical applications. To achieve the purpose of being safe and user friendly, these devices have been developed to avoid electric shock and thermal damage. These types of plasma equipment operate with a sinusoidal voltage of kilovolts at a low frequency of several tens of kilohertz. The plasma jets have been developed with the specific ground-electrode structures according to the various gases in use, such as inert gases, molecular gases, or mixture gases, and air. The Ar-plasma jet with the external ground electrode is operated in a low current of 1–2 mA with the voltage of 1–2 kV. The stable air-jet plasma/plume exiting from a small hole at the cold metal-cap nozzle of the ground electrode can be obtained in a low current of 0.5–1 mA for safety with the voltage of 5–10 kV. Both types of ground electrode, the external electrode and the metal-cap electrode, are applicable to the plasma jets of molecular or mixture gases. The devices for DBD plasmas are shown to be the new advents of plasma stamp, plasma stick, plasma comb, and plasma roller, which operate with the voltage of 2–3 kV.

In this paper, we present design and measurement of LNA(Low Noise Amplifier) based on GaN HEMT(Gallium Nitride High Electron Mobility Transistor) to reduce the total noise figure of radar receiver and for robustness of LNA. In radar receiver using LNA based on GaAs(Gallium Arsenide) technology, limiter is necessary at the very front of the radar receiver to protect LNA. As a result, total noise figure of radar receiver is deteriorated. In this research, measured noise figure of LNA based on GaN HEMT is below 2 dB. In the case of commercialized GaAs LNA, recommended maximum input power is about 30 dBm. On the other hand, GaN HEMT LNA which is designed and measured is burned-out when input power is 43 dBm and robustness is guaranteed at input power 45.4 dBm. Key words: LNA, GaN HEMT, Robustness, Current Limit ‡wx ˆ3‰Š 5wx‹9Œ wx . Ž ‘+C’“(Department of Wireless Communications Engineering,, Kwangwoon University) *ˆ3‰Š(Samsung Thales, Co, Ltd) `Manuscript received December 24, 2014 ; Revised February 5, 2015 ; Accepted February 6, 2015. (ID No. 20141224-105)`Corresponding Author: Jin-Joo Choi (e-mail: jinchoi@kw.ac.kr)

Taking advantage of X-ray LIGA system, we fabricated sub-teraherz folded waveguide circuits. Small signal gain in a W-band folded waveguide TWT was measured to be 15 dB. Folded waveguide circuits operating at both 220 GHz and 850 GHz were fabricated. Cold tests shows 10 dB return loss and 6 dB transmission characteristics of circuits in G-band.

Having the device simplicity and high output-power capacity, the capability of the virtual cathode oscillator (vircator) for emitting high power microwaves is demonstrated. We have investigated the axial-typed vircator in our pulsed power generator, “Chundoong” (Max 600 kV, 88 kA, and 60 ns), and simulated the vircator using the 3-D particle-in-cell simulation code called “MAGIC.” We try to find out the position of the virtual cathode inside the drift tube and enhance the power of microwaves by focusing them at the focus point using the ring-typed zone plate with a focal length of 18.8 cm. The dominant frequency is obtained as 3.5 GHz measured by fast Fourier transform, which is in good agreement with simulation frequency. It is found that the mean position of the virtual cathode is almost the same as the A-K gap distance of 10 mm, in which the virtual cathode oscillates from 7.9 mm to 12.1 mm behind the meshed anode, as verified by the simulation results. The maximum output power without the zone plate is obtained as 0.66 GW with the efficiency of 27%, which is maximized up to 1.22 GW with the efficiency of 51% at the focus point by using the zone plate. The microwave emission mode from the vircator is the TM01 mode based on the simulation results. The zone plate contributes significantly in enhancing the power efficiency and determination of the position of the virtual cathode. These observations might be used in developing a high efficient microwave source by using a zone plate under the decision of the position of the virtual cathode.