Dongkyu Kim

Nonvacuum, Maskless Fabrication of a Flexible Metal Grid Transparent Conductor by Low-Temperature Selective Laser Sintering of Nanoparticle Ink

We introduce a facile approach to fabricate a metallic grid transparent conductor on a flexible substrate using selective laser sintering of metal nanoparticle ink. The metallic grid transparent conductors with high transmittance (>85%) and low sheet resistance (30 Ω/sq) are readily produced on glass and polymer substrates at large scale without any vacuum or high-temperature environment. Being a maskless direct writing method, the shape and the parameters of the grid can be easily changed by CAD data. The resultant metallic grid also showed a superior stability in terms of adhesion and bending. This transparent conductor is further applied to the touch screen panel, and it is confirmed that the final device operates firmly under continuous mechanical stress.

A Survey of In-Band Full-Duplex Transmission: From the Perspective of PHY and MAC Layers

In-band full-duplex (IBFD) transmission represents an attractive option for increasing the throughput of wireless communication systems. A key challenge for IBFD transmission is reducing self-interference. Fortunately, the power associated with residual self-interference can be effectively canceled for feasible IBFD transmission with combinations of various advanced passive, analog, and digital self-interference cancellation schemes. In this survey paper, we first review the basic concepts of IBFD transmission with shared and separated antennas and advanced self-interference cancellation schemes. Furthermore, we also discuss the effects of IBFD transmission on system performance in various networks such as bidirectional, relay, and cellular topology networks. This survey covers a wide array of technologies that have been proposed in the literature as feasible for IBFD transmission and evaluates the performance of the IBFD systems compared to conventional half-duplex transmission in connection with theoretical aspects such as the achievable sum rate, network capacity, system reliability, and so on. We also discuss the research challenges and opportunities associated with the design and analysis of IBFD systems in a variety of network topologies. This work also explores the development of MAC protocols for an IBFD system in both infrastructure-based and ad hoc networks. Finally, we conclude our survey by reviewing the advantages of IBFD transmission when applied for different purposes, such as spectrum sensing, network secrecy, and wireless power transfer.

The alteration of enterochromaffin cell, mast cell, and lamina propria T lymphocyte numbers in irritable bowel syndrome and its relationship with psychological factors

Background/Aims:  Psychological factors and subtle histopathological changes have been implicated in irritable bowel syndrome (IBS). The aims of the present study were to investigate whether the numbers of enterochromaffin (EC) cells, mast cells, and lamina propria T lymphocytes are altered in IBS, and evaluate the relationship of such alterations with psychological factors.

Selective Induction of Apoptosis with Proton Pump Inhibitor in Gastric Cancer Cells

Purpose: To survive in an ischemic microenvironment with a lower extracellular pH, ability to up-regulate proton extrusion is critical for cancer cell survival. Gastric H+/K+-ATPase exchanges luminal K+ for cytoplasmic H+ and is the enzyme primarily responsible for gastric acidification. On the basis of the fact that blocking the clearance of acidic metabolites are known to induce the cell death, we hypothesized that pantoprazole (PPZ), one of gastric H+/K+-ATPase inhibitors used frequently to treat acid-related diseases, could inhibit growth of tumor cells. Experimental Design: Genomic DNA fragmentation, terminal deoxynucleotidyl transferase (Tdt)-mediated nick end labeling assay, and annexin V staining were performed to detect PPZ-induced apoptosis. Mitogen-activated protein kinase activation and heat shock proteins expression were determined by immunoblot with specific antibodies. The antitumor effect of PPZ was evaluated in vivo by a xenograft model of nude mice. Results: After PPZ treatment, apoptotic cell death was seen selectively in cancer cells and was accompanied with extracellular signal-regulated kinase deactivation. By contrast, normal gastric mucosal cells showed the resistance to PPZ-induced apoptosis through the overexpression of antiapoptotic regulators including HSP70 and HSP27. In a xenograft model of nude mice, administration of PPZ significantly inhibited tumorigenesis and induced large-scale apoptosis of tumor cells. Conclusions: PPZ selectively induced in vivo and in vitro apoptotic cell death in gastric cancer, suggesting that proton pump inhibitors could be used for selective anticancer effects.

Pepsin Detection in the Sputum/Saliva for the Diagnosis of Gastroesophageal Reflux Disease in Patients with Clinically Suspected Atypical Gastroesophageal Reflux Disease Symptoms

Background/Aims: Atypical manifestations of gastroesophageal reflux disease (GERD) are diverse. We aimed to determine whether pepsin detection in the sputum/saliva could be useful for diagnosing GERD in patients with clinically suspected atypical GERD symptoms. Methods: Patients with clinically suspected atypical GERD symptoms provided sputum/saliva collected before bedtime, at the time of those symptoms, and after awakening for pepsin measurement by Western blot analysis. All subjects received 24-hour esophageal pH monitoring, and then 40 mg of esomeprazole was given twice a day for 2 weeks. Results: The pepsin test was positive in 20 out of 40 patients, with pepsin detected mainly in the samples collected at the time of symptoms (45%). Samples collected from healthy volunteers (n = 8) were all negative for pepsin. 24-hour pH-metry was positive in 9 patients (23%). Based on 24-hour pH-metry data, the sensitivity and negative predictive value of the pepsin test were excellent in most of typical and atypical symptom groups, whereas its specificity and positive predictive value were relatively low, particularly in atypical symptom groups. Conclusions: Pepsin measurement in the sputum/saliva collected at the time of symptoms provides a sensitive, non-invasive method for diagnosing GERD in patients with clinically suspected atypical GERD symptoms.

Effects of Channel Estimation Error on Full-Duplex Two-Way Networks

Bidirectional communication systems based on full-duplex transmission have been proposed as a way to increase the ergodic capacity of multiantenna two-way networks. This type of system enables simultaneous exchange of data between two nodes via bidirectional use of spatial resources. However, when channel estimation error is present, each node experiences both desired-channel interference (DI) and echo-channel interference (EI). This paper investigates the effect of channel estimation errors on the ergodic capacities for bidirectional full-duplex transmission (BFD) using one of two combining schemes: maximal-ratio combining (MRC) or optimum combining (OC). We derive the ergodic capacities as closed-form expressions and quantify the effect of channel estimation errors on ergodic capacities for BFD with MRC (BFD-MRC) or OC (BFD-OC). Numerical results demonstrate that full-duplex transmission in two-way networks is an attractive option when channel estimation error is present.

Advanced sensing techniques of energy detection in cognitive radios

Recently, spectrum sensing has been intensively studied as a key technology in realizing the cognitive radio. There have been advances in the performance of spectrum sensing through both multi-antenna and cooperative sensing schemes. In this paper, the performances and complicated scenarios of the latest spectrum sensing schemes are analytically compared and arranged into a technical tree while considering practical concerns. This paper will give a macroscopic view of spectrum sensing and will also provide insight into future spectrum sensing works.

Full Duplexity in Beamforming-Based Multi-Hop Relay Networks

This work investigates the effects of full duplexity on delay and throughput in interference-limited multi-hop networks. It is assumed that channel state information is not available at transmitters and beamforming is employed as the transmission scheme. A closed-form expression is developed for hop success probability in networks of this type. The delay and throughput of multi-hop networks employing full duplex and half duplex beamforming are than compared. The delay and throughput are studied in two cases: when full duplexity is used for full duplex relay (FDR), and bi-directional beamforming (BBF). For FDR, employing full duplex beamforming is more beneficial if a low rate constraint is required or if interferers are rare. However, this benefit diminishes as the required data rate or the interferer density increases. For BBF, the use of full duplex beamforming is always more beneficial because it leads to a reduction in the required rate constraint. Specifically, this benefit becomes more significant as the required rate rises and interferers become rarer.

Effect of Bluetooth interference on OFDM-based WLAN

Bluetooth systems result in unintentional interference to OFDM systems using industry, science and medical (ISM) bands. The performance degradation of orthogonal frequency division multiplexing (OFDM) systems from Bluetooth interference is analyzed numerically. Bluetooth interference is modeled on partial band jamming with a rectangular spectrum. Bit error probability (BEP) performance based on the effective signal-to-noise power ratio (SNR) is provided for OFDM systems in Rayleigh fading channels in addition to AWGN. Additionally, coding gain over Bluetooth interference is evaluated for an OFDM-based wireless local area network (WLAN) in IEEE 802.11g.

Facial amphipathic deoxycholic acid-modified polyethyleneimine for efficient MMP-2 siRNA delivery in vascular smooth muscle cells

Clinical applications of RNA interference-based therapeutics such as small interfering RNAs (siRNAs) have been limited mainly due to low intracellular delivery efficiency in vitro and in vivo. In this study, facially amphipathic deoxycholic acid (DA)-modified polyethyleneimine (PEI(1.8)) (DA-PEI(1.8)) was synthesized and used as a potent carrier system for siRNA targeted against matrix metalloproteinase-2 (MMP-2) to inhibit the migration of vascular smooth muscle cells (SMCs), which is the major pathomechanism in the development of atherosclerosis and restenosis after arterial injury. A representative facial amphipathic bile acid DA having a high membrane permeability was conjugated to the terminal amine groups of the low molecular weight PEI(1.8) via amide bonds. The DA-PEI(1.8) conjugates formed self-assembled nanoparticles with siRNA molecules in an aqueous phase and the DA-PEI(1.8)/siRNA polyplexes became stabilized and condensed as particle incubation time increased from 0 to 4h. Both cellular internalization and target gene silencing were enhanced as the DA-PEI(1.8)/siRNA polyplexes stabilized. When vascular SMCs were transfected with MMP-2 siRNA, the DA-PEI(1.8)/siRNA polyplex formulation led to a significant decrease in MMP-2 gene expression, resulting in the suppression of cell migration. These results suggest that the DA-PEI(1.8)/MMP-2 siRNA delivery system may be useful in anti-restenotic treatment for various vasculoproliferative disorders such as atherosclerosis, in-stent restenosis, and vein graft failure.