Sliding elastic lattice: an explanation of the motion of superconducting vortices

We introduce a system where an elastic lattice of particles is moved slowly at a constant velocity under the influence of a local external potential, construct a rigid-body model through simplification processes, and show that the two systems produce similar results. Then, we apply our model to a superconducting vortex system and produce path patterns similar to the ones reported in [Lee et al., Phys. Rev. B 84, 060515 (2011)] suggesting that the reasoning of the simplification processes in this paper can be a possible explanation of the experimentally observed phenomenon.Comment: 5 pages, 3 figures, Submitted to Physical Review Letters; Reference [17] Lee et al., Phys. Rev. B Accepted changed to Lee et al., Phys. Rev. B 84, 060515 (2011

Atomic resolution imaging at 2.5 GHz using near-field microwave microscopy

Atomic resolution imaging is demonstrated using a hybrid scanning tunneling/near-field microwave microscope (microwave-STM). The microwave channels of the microscope correspond to the resonant frequency and quality factor of a coaxial microwave resonator, which is built in to the STM scan head and coupled to the probe tip. We find that when the tip-sample distance is within the tunneling regime, we obtain atomic resolution images using the microwave channels of the microwave-STM. We attribute the atomic contrast in the microwave channels to GHz frequency current through the tip-sample tunnel junction. Images of the surfaces of HOPG and Au(111) are presented.Comment: 9 pages, 5 figures, submitted to Applied Physics Letter

Low Temperature Scanning Tunneling Microscope Development: Investigations of Au(111) and Ultra-slow Vortex Dynamics of NbSe2

We report the development of a scanning tunneling microscope (STM), operating at 4.2 K, high magnetic field, and ultra-high vacuum (UHV), and the measurements of Au(111) and NbSe2 with/without magnetic fields. The STM showed horizontal and vertical scan-ranges of 1.0×1.0 μm2 and 270 nm, respectively. As of now, STM measurements have been carried out in a field up to 1 T. The UHV facility for tip/sample preparation in clean environment was integrated into the STM system. The nominal pressure of ~10-10 mbar in UHV chambers was achieved. However, the data of Au(111) and NbSe2 were taken before installation of the UHV system. We observed the standing wave of surface state electron of Au(111) by carrying out a conductance map. We found an effective mass of surface state electron of m* = 0.24me, where me is the mass of a free electron. We also observed the motion of Au steps when the STM continued scanning. As steps moved, the patterns of herringbone reconstruction on the surface also changed in a complex way. This atomic motion probably resulted from the tip-sample interaction in a stressed film. Using pristine NbSe2, we observed the charge density wave (CDW) and superconducting states simultaneously at 4.2 K via topographic/spectroscopic measurements. The well-known √3×√3 superstructure of CDW state was revealed in topography. Furthermore, we deliberately introduced two additional phases (√13×√13 and amorphous) by changing a bias voltage from 1-100 mV to 5-10 V. This in situ surface modification can be used in studying the competition between superconducting and CDW states. Lastly, we show that the study of vortex dynamics on the nano-meter scale was achieved by utilizing an extremely slow decay of the magnetic field in the superconducting magnet as the driving source. The field decay rate of ~ nT/s caused vortices to move at ~ pm/s so that the temporal resolution of our STM was sufficient to image these slowly moving vortices. Furthermore, this vortex driving mechanism can be utilized to study vortex dynamics of various superconductors on the nano-meter scale in STM experiments

Malware Visualization and Similarity via Tracking Binary Execution Path

Today, computer systems are widely and importantly used throughout society, and malicious codes to take over the system and perform malicious actions are continuously being created and developed. These malicious codes are sometimes found in new forms, but in many cases they are modified from existing malicious codes. Since there are too many threatening malicious codes that are being continuously generated for human analysis, various studies to efficiently detect, classify, and analyze are essential. There are two main ways to analyze malicious code. First, static analysis is a technique to identify malicious behaviors by analyzing the structure of malicious codes or specific binary patterns at the code level. The second is a dynamic analysis technique that uses virtualization tools to build an environment in a virtual machine and executes malicious code to analyze malicious behavior. The method used to analyze malicious codes in this paper is a static analysis technique. Although there is a lot of information that can be obtained from dynamic analysis, there is a disadvantage that it can be analyzed normally only when the environment in which each malicious code is executed is matched. However, since the method proposed in this paper tracks and analyzes the execution stream of the code, static analysis is performed, but the effect of dynamic analysis can be expected.The core idea of this paper is to express the malicious code as a 25 25 pixel image using 25 API categories selected. The interaction and frequency of the API is made into a 25 25 pixel image based on a matrix using RGB values. When analyzing the malicious code, the Euclidean distance algorithm is applied to the generated image to measure the color similarity, and the similarity of the mutual malicious behavior is calculated based on the final Euclidean distance value. As a result, as a result of comparing the similarity calculated by the proposed method with the similarity calculated by the existing similarity calculation method, the similarity was calculated to be 5-10% higher on average. The method proposed in this study spends a lot of time deriving results because it analyzes, visualizes, and calculates the similarity of the visualized sample. Therefore, it takes a lot of time to analyze a huge number of malicious codes. A large amount of malware can be analyzed through follow-up studies, and improvements are needed to study the accuracy according to the size of the data set

Design of Automation Environment for Analyzing Various IoT Malware

With the increasing proliferation of IoT systems, the security of IoT systems has become very important to individuals and businesses. IoT malware has been increasing exponentially since the emergence of Mirai in 2016. Because the IoT system environment is diverse, IoT malware also has various environments. In the case of existing analysis systems, there is no environment for dynamic analysis by running IoT malware of various architectures. It is inefficient in terms of time and cost to build an environment that analyzes malware one by one for analysis. The purpose of this paper is to improve the problems and limitations of the existing analysis system and provide an environment to analyze a large amount of IoT malware. Using existing open source analysis tools suitable for various IoT malicious codes and QEMU, a virtualization software, the environment in which the actual malicious code will run is built, and the library or system call that is actually called is statically and dynamically analyzed. In the text, the analysis system is applied to the actual collected malicious code to check whether it is analyzed and derive statistics. Information on the architecture of malicious code, attack method, command used, and access path can be checked, and this information can be used as a basis for malicious code detection research or classification research. The advantages are described of the system designed compared to the most commonly used automated analysis tools and improvements to existing limitations

Extended Axion Dark Matter Search Using the CAPP18T Haloscope

We report an extended search for the axion dark matter using the CAPP18T haloscope. The CAPP18T experiment adopts innovative technologies of a high-temperature superconducting magnet and a Josephson parametric converter. The CAPP18T detector was reconstructed after an unexpected incident of the high-temperature superconducting magnet quenching. The system reconstruction includes rebuilding the magnet, improving the impedance matching in the microwave chain, and mechanically readjusting the tuning rod to the cavity for improved thermal contact. The total system noise temperature is $\sim$0.6\,K. The coupling between the cavity and the strong antenna is maintained at $\beta \simeq 2$ to enhance the axion search scanning speed. The scan frequency range is from 4.8077 to 4.8181 GHz. No significant indication of the axion dark matter signature is observed. The results set the best upper bound of the axion-photon-photon coupling ($g_{a\gamma\gamma}$) in the mass ranges of 19.883 to 19.926\,$\mu$eV at $\sim$0.7$\times|g_{a\gamma\gamma}^{\text{KSVZ}}|$ or $\sim$1.9$\times|g_{a\gamma\gamma}^{\text{DFSZ}}|$ with 90\,\% confidence level. The results demonstrate that a reliable search of the high-mass dark matter axions can be achieved beyond the benchmark models using the technology adopted in CAPP18T.Comment: 7 pages and 4 figure