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Recent advancements in data science technologies have allowed researchers to utilize large-scale records of human mobility to study various topics from city growth models to tracing outbreaks and analyzing the labor market. In this paper, after introducing recent studies on human mobility using transportation data, we briefly review the existing studies by applying large-scale human mobility data to three different topics: epidemics, economics, and science of science. As the early attempts of interdisciplinary studies, these studies reveal how human mobility records can help us solve significant social, economic, and public health issues in our era.

In this article, we investigate dynamics of electrically driven abrupt and volatile resistive switching characteristics, which are called threshold switching (TS) characteristics, in insulator-to-metal transition NbO x switch, BTe x -based ovonic threshold switch, and Ag-based atomic switch by adopting field-induced nucleation theory. To verify field-induced nucleation phenomena in the initial electroforming and electrically driven TS processes of the TS devices, we apply constant square voltage pulses with various voltage magnitudes and measure the delay time required for the electrical switching process. During both the forming and switching processes, it is observed that all the TS devices exhibit switching delay time exponential in 1/voltage with different nucleation barrier energies ( ${W}_{{0}}$ ). In addition, we find that the ${W}_{{0}}$ for the first forming process appears to be larger than that for the subsequent switching process and the difference is observed to be greater if the formed device is crystallized and smaller if not. Moreover, we find that the effective barrier energy and the fastest speed that a device can have ( $\tau _{{0}}$ ) are closely related to switching speed of the TS devices. Also, we reveal that the hold voltage characteristics are affected by the ${W}_{{0}}$ and carrier concentration of the solid electrolyte.

Emerging nonvolatile memory devices, also named memristive devices, have drawn great attention due to their potential for ultra-high density memory application. To achieve such high-density memristive device, a crossbar array structure is introduced. However, implementing such crossbar array requires addressing issues such as unwanted current flow in the unselected cell, so-called the “sneak-path” current. Therefore an access device called a selector device is required to suppress such undesired current and to operate the target memory cell both selectively and nondestructively in the crossbar array. Although different kinds of selector devices have been studied, none of them met all requirements, such as simple two-terminal structure, highly nonlinear I–V characteristics, fast operation speed, high endurance, excellent uniformity, and good thermal stability. The insulator–metal transition (IMT), the ovonic threshold switching (OTS), and the conductive bridging RAM (CBRAM)-type device are promising candidates as a selector device due to their scalability. IMT- and OTS-based selectors exhibit excellent performance, such as high on-current density and extremely fast switching speed, but the off-current, especially for IMT-based selectors, still needs further improvement for the effective reduction of leakage current in the crossbar array. CBRAM-type selectors have ultralow leakage current, suitable for high selectivity and low power device applications. However, the poor on-current density and reliability issues hinder their applicability. There has been great effort to improve the performance of these three types of selector devices, and this chapter reviews recent progress and future directions on their implementation for high-density crossbar array.

In this letter, we demonstrate a new concept of threshold selector by combining Ag-based selector with NbO x insulator metal transition (IMT) selector. To overcome intrinsic limits of slow turn-off speed ( $> 1\mu \text{s}$ ) of the Ag-based selector, we adopted NbO x IMT selector with fast turn-off speed. The hybrid device exhibits excellent selector characteristics, such as extremely low off-current ( $ ). It shows excellent read-out margin (>75% at >210 word lines) in a fast sequential operation of cross point memory array.

In this letter, a new ovonic threshold switch (OTS) device based on simple binary Boron–Tellurium (B–Te) film is developed and implemented in series with the source region of a transistor. The newly developed B–Te-based device shows excellent characteristics such as low operating voltage, low leakage current, abrupt turn-on/off slope, fast switching speed, high endurance, and high thermal stability. Due to the great properties of the B–Te OTS device, the implemented transistor exhibits subthreshold swing less than 10 mV/dec and high on/off current ratio greater than $10^{5}$ . Moreover, we present a direction of implementing an ideal transistor based on simulation results explaining the effect of off-state resistances and threshold voltages of the OTS devices on the $I_{\mathrm{ DS}}$ - $V_{\mathrm{ GS}}$ characteristics of the implementer transistor.

Groups of firms often achieve a competitive advantage through the formation of geo-industrial clusters. Although many exemplary clusters are the subjects of case studies, systematic approaches to identify and analyze the hierarchical structure of geo-industrial clusters at the global scale are scarce. In this work, we use LinkedIn’s employment history data from more than 500 million users over 25 years to construct a labor flow network of over 4 million firms across the world, from which we reveal hierarchical structure by applying network community detection. We show that the resulting geo-industrial clusters exhibit a stronger association between the influx of educated workers and financial performance, compared to traditional aggregation units. Furthermore, our analysis of the skills of educated workers reveals richer insights into the relationship between the labor flow of educated workers and productivity growth. We argue that geo-industrial clusters defined by labor flow provide useful insights into the growth of the economy., There is a lack of systematic approaches to identify and analyze the hierarchical structure of geo-industrial clusters at the global scale. Here the authors use LinkedIn's employment history data to construct a global labor flow network from which they find that the resulting geo-industrial clusters exhibit a stronger association between the influx of educated-workers and financial performance compared to existing aggregation units.

This paper examines network prominence in a co-prescription network as an indicator of opioid doctor shopping (i.e., fraudulent solicitation of opioids from multiple prescribers). Using longitudinal data from a large commercially insured population, we construct a network where a tie between patients is weighted by the number of shared opioid prescribers. Given prior research suggesting that doctor shopping may be a social process, we hypothesize that active doctor shoppers will occupy central structural positions in this network. We show that network prominence, operationalized using PageRank, is associated with more opioid prescriptions, higher predicted risk for dangerous morphine dosage, opioid overdose, and opioid use disorder, controlling for number of prescribers and other variables. Moreover, as a patient’s prominence increases over time, so does their risk for these outcomes, compared to their own average level of risk. Results highlight the importance of co-prescription networks in characterizing high-risk social dynamics.

Emerging storage devices based on new physical switching mechanisms (noncharge based) have received great interest to implement ultrahigh-density crossbar arrays. However, in addition to the introduction of these new memory devices, implementing crossbar arrays requires addressing issues such as undesired current flow and data disturbance in nonselected cells. Therefore, an access device called a selector device is required to selectively operate and read the target device in the crossbar array. Though many selector devices have been researched, the ideal selector device to meet the requirements for a crossbar array architecture such as two-terminal structure, highly nonlinear I-V characteristics, fast switching speed, and excellent device uniformity has not been reported yet. Therefore, this chapter reviews the previously reported selector devices and discusses the development direction of the selector devices.

In this study, we investigate the initial electroforming and electrically driven threshold switching characteristics of a binary boron-tellurium-based ovonic threshold switch (OTS) device using field-induced nucleation theory and related material parameters. First, an analysis of the current-voltage characteristics of devices with various electrode areas shows that the OTS device exhibits filamentary switching, consistent with the field-induced nucleation framework. Further, we find that the OFF-state current depends on the device area, whereas the hold current remains constant regardless of the device area, indicating that the ON-state current flows through a local conduction path. For verifying field-induced nucleation phenomena in the forming and subsequent switching of the OTS device, we apply constant voltage pulses and measure the delay time required for electrical switching of the device. During both forming and switching processes, the switching time is exponential in inverse voltage with different nucleation energy (W0) values; W0 for forming is larger than that for switching. To verify this analysis, incremental voltage pulses with various pulse widths are also applied to confirm the relation between the threshold voltage and time. The W0 values for the two types of switching in this analysis are consistent, solidifying our understanding of the critical contribution of nucleation phenomena in OTS. The smaller W0 for switching can be explained by the generation of clusterlike nucleation sites during forming with lower nucleation energy than in the surrounding matrix.

We have investigated various Te-based binary materials for Ovonic Threshold Switch (OTS) selector application. We found that both Te composition and difference in atomic radius of elements composing the telluride film are the key control parameters to maximize the OTS characteristics such as low leakage current (

To realize a steep slope field-effect transistor (FET) with low leakage current and controllable operating bias, NbO2 threshold switching (TS) device is connected in series with the gate side of a MOSFET. Thanks to the TS device showing abrupt transition between the OFF and ON states at threshold voltage (Vth), the implemented transistor exhibits extremely low leakage current (10−7μA/μm), high I on /I off ratio (>106), sub-2 mV/dec subthreshold swing, drift-free characteristic and high temperature operation (>85°C). Furthermore, since the Vth is tunable by controlling thickness of the NbO 2 TS device, the new NbO 2 -MOSFET can fulfill various demands of operating bias conditions. In addition, we confirmed through a simulation that the CMOS inverter with NbO 2 connected to the gate side showed fast inverting speed of over 300 MHz at ultra-low voltage ( d (ΔV>200mV).

The switching uniformity and reliability of the TaOx based resistive random access memory (RRAM) device were investigated with varying nitrogen doping concentration. The nitrogen doped samples shows excellent electrical and reliability characteristics such as small switching variability for 3-bit multilevel per cell (MLC), low power operation and good retention properties. Compared with control sample, improved device characteristics of nitrogen doped device can be explained by nitrogen inducedfilament confinement. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

NbO2 has the potential for a variety of electronic applications due to its electrically induced insulator-to-metal transition (IMT) characteristic. In this study, we find that the IMT behavior of NbO2 follows the field-induced nucleation by investigating the delay time dependency at various voltages and temperatures. Based on the investigation, we reveal that the origin of leakage current in NbOx is partly due to insufficient Schottky barrier height originating from interface defects between the electrodes and NbOx layer. The leakage current problem can be addressed by inserting thin NiOy barrier layers. The NiOy inserted NbOx device is drift-free and exhibits high Ion/Ioff ratio (>5400), fast switching speed (453 K) characteristics which are highly suitable to selector application for x-point memory arrays. We show that NbOx device with NiOx interlayers in series with resistive random access memory (ReRAM) device demonstrates improved readout margin (>29 word lines) suitable for x-point memory array application.

NbO2 has the potential for a variety of electronic applications due to its electrically induced insulator-to-metal transition (IMT) characteristic. In this study, we find that the IMT behavior of NbO2 follows the field-induced nucleation by investigating the delay time dependency at various voltages and temperatures. Based on the investigation, we reveal that the origin of leakage current in NbOx is partly due to insufficient Schottky barrier height originating from interface defects between the electrodes and NbOx layer. The leakage current problem can be addressed by inserting thin NiOy barrier layers. The NiOy inserted NbOx device is drift-free and exhibits high Ion/Ioff ratio (>5400), fast switching speed (453 K) characteristics which are highly suitable to selector application for x-point memory arrays. We show that NbOx device with NiOx interlayers in series with resistive random access memory (ReRAM) device demonstrates improved readout margin (>29 word lines) suitable for x-point memory array application.

AgTe/TiN/TiO 2 /TiN threshold switching (TS) device was monolithically integrated with silicon MOSFET to demonstrate steep subthreshold slope field-effect transistors. The TS device with AgTe top electrode showed the high on-current, since the Te allows an extraction of the Ag out of the filament. The TiN liner was also inserted at the AgTe/TiO 2 interface to prevent in-diffusion of Ag into the TiO2 layer during back-end-of-line process. Finally, the transistor with TS device has a sub-5-mV/dec subthreshold slope (SS) and a high on/off current ratio (Ion/I off ) of >108 with a low drain voltage (0.5 V) even after the 400°C annealing process.

To realize a steep-slope-FET with low leakage current and low operating bias, we engineered two types of atom-switch devices and integrated them with a silicon MOSFET. The integrated atom-switch-FET exhibits extremely low leakage current (10−7 μA/μm), high I on /I off ratio (> 107), low operating bias ( off and Vth, as for optimal performances of atom-switch-FET were investigated at various operating bias conditions.

Display Omitted We deposit the two types of NbOx selector which are single-layer NbOx and multi-layer NbOx selector.The multi-layer NbOx selector has about 3-5 times improved properties than single-layer NbOx selector.The regions of leakage current at the off-state of NbOx selector are revealed by using C-AFM tool.The barrier layer of multi-layer NbOx selector reduce the leakage region. In this paper, a multi-layer NbOx selector is fabricated and compared with a single-layer NbOx selector. The multi-layer NbOx selector exhibits better performances ( 106 endurance) than the single-layer NbOx selector. By using a conductive atomic force microscopy (C-AFM), we revealed that numerous leakage paths in the NbOx film can be suppressed by adopting an insulating barrier layer within the multi-layer NbOx selector.

Inactivation of the gene coding for dihydroflavonol 4-reductase (DFR) is responsible for the color difference between red and yellow onions (Allium cepa L.). Two inactive DFR-A alleles, DFR-A PS and DFR-A DEL , were identified in our previous study. A functional marker was developed on the basis of the premature stop codon that inactivated the DFR-A PS allele. A derived cleaved amplified polymorphic sequences (dCAPS) primer was designed to detect the single nucleotide polymorphism, an A/T transition, which produced the premature stop codon. Digested PCR products clearly distinguished the homozygous and heterozygous red F₂ individuals. Meanwhile, to develop a molecular marker for detection of the DFR-A DEL allele in which entire DFR-A gene was deleted, genome walking was performed and approximately 3 kb 5’ and 3’ flanking sequences of the DFR-A R coding region were obtained. PCR amplification using multiple primers binding to the extended flanking regions showed that more of the extended region of the DFR-A gene was deleted in the DFR-A DEL allele. A dominant simple PCR marker was developed to identify the DFR-A DEL allele using the dissimilar 3’ flanking sequences of the DFR-A gene and homologous DFR-B pseudogene. Distribution of the DFR-A PS and DFR-A DEL alleles in yellow onion cultivars bred in Korea and Japan was surveyed using molecular makers developed in this study. Results showed predominant existence of the DFR-A PS allele in yellow onion cultivars.

We investigate the effect of Cu concentration On-state resistance retention characteristics of W/Cu/Ti/HfO2/Pt memory cell. The development of RRAM device for application depends on the understanding of the failure mechanism and the key parameters for device optimization. In this study, we develop analytical expression for cations (Cu+) diffusion model using Gaussian distribution for detailed analysis of data retention time at high temperature. It is found that the improvement of data retention time depends not only on the conductive filament (CF) size but also on Cu atoms concentration density in the CF. Based on the simulation result, better data retention time is observed for electron wave function associated with Cu+ overlap and an extended state formation. This can be verified by analytical calculation of Cu atom defects inside the filament, based on Cu+ diffusion model. The importance of Cu diffusion for the device reliability and the corresponding local temperature of the filament were analyzed by COMSOL Multiphysics simulation. (C) 2016 Author(s).

In this paper, we demonstrate a volatile atomic switch that can be utilized for obtaining steep subthreshold swing (SS) ( 60 mV/dec). The result shows an improvement in the SS, which results from the transition of the atomic switch between the ON and OFF states, which is caused by the formation and rupture of a conductive filament. As a result, excellent switching characteristics are obtained for the FETs, such as low IOFF (∼10−5 μA/μm), high ION/IOFF ratio (∼105), low VDD (∼0.25 V), and steep SS ( 60 mV/dec). The result shows an improvement in the SS, which results from the transition of the atomic switch between the ON and OFF states, which is caused by the formation and rupture of a conductive filament. As a result, excellent switching characteristics are obtained for the FETs, such as low IOFF (∼10−5 μA/μm), high ION/IOFF ratio (∼105), low VDD (∼0.25 V), and steep SS (

In this letter, we demonstrate a new binary ovonic threshold switching (OTS) selector device scalable down to o30 nm based on C–Te. Our proposed selector device exhibits outstanding performance such as a high switching ratio (Ion/Ioff > 105), an extremely low off-current (~1 nA), an extremely fast operating speed of 450 °C). The observed high thermal stability is caused by the relatively small atomic size of C, compared to Te, which can effectively suppress the segregation and crystallization of Te in the OTS film. Furthermore, to confirm the functionality of the selector in a crossbar array, we evaluated a 1S-1R device by integrating our OTS device with a ReRAM (resistive random access memory) device. The 1S-1R integrated device exhibits a successful suppression of leakage current at the half-selected cell and shows an excellent read-out margin (>212 word lines) in a fast read operation.

Fashion is a multi-billion dollar industry with social and economic implications worldwide. To gain popularity, brands want to be represented by the top popular models. As new faces are selected using stringent (and often criticized) aesthetic criteria, \emph{a priori} predictions are made difficult by information cascades and other fundamental trend-setting mechanisms. However, the increasing usage of social media within and without the industry may be affecting this traditional system. We therefore seek to understand the ingredients of success of fashion models in the age of Instagram. Combining data from a comprehensive online fashion database and the popular mobile image-sharing platform, we apply a machine learning framework to predict the tenure of a cohort of new faces for the 2015 Spring\,/\,Summer season throughout the subsequent 2015-16 Fall\,/\,Winter season. Our framework successfully predicts most of the new popular models who appeared in 2015. In particular, we find that a strong social media presence may be more important than being under contract with a top agency, or than the aesthetic standards sought after by the industry., 10 pages, 5 figures, accepted for presentation at CSCW'16

In this research, an one selector-one ReRAM (1S1R) cross-point array of a multi-level cell (MLC) was demonstrated and investigated. To expand high-density feasibility of cross-point array, MLC pulse writing and reading operations were assessed with parasitic line resistances and capacitances using Matlab and HSPICE simulations. We observed a switching energy is an important parameter for MLC in actual cross-point array in the operating point of view. In addition, not only ReRAM but also selector characteristics are highly important in the device point of view. Therefore, this study serves power efficient guidelines for 1S1R devices and operating schemes of cross-point array.

In this paper, we investigate the quantized conduction behavior of conductive bridge random access memory (CBRAM) with varied materials and ramping rates. We report stable and reproducible quantized conductance states with integer multiples of fundamental conductance obtained by optimizing the voltage ramping rate and the Ti-diffusion barrier (DB) at the Cu/HfO2 interface. Owing to controlled diffusion of Cu ions by the Ti-DB and the optimized ramping rate, through which it was possible to control the time delay of Cu ion reduction, more than seven levels of discrete conductance states were clearly observed. Analytical modeling was performed to determine the rate-limiting step in filament growth based on an electrochemical redox reaction. Our understanding of the fundamental mechanisms of quantized conductance behaviors provide a promising future for the multi-bit CBRAM device.

We demonstrate the device characteristics of W/Cu/N-GST/Al 2 O 3 /Pt conductive-bridging RAM, focusing on the nitrogen-doped Ge 2 Sb 2 Te 5 buffer layer to realize non-volatile memory applications. The on/off ratio of typical Cu/Al 2 O 3 -based CBRAM was improved from 102 to 105 with the N-GST buffer layer. The switching uniformity also improved compared to that of a non-buffer layer device. The improved properties that were realized are attributed to the effects of buffer layer such as controlled Cu-ion injection, internal resistor, and Joule heating confinement during the reset process. Furthermore, to verify the effect of nitrogen on the switching properties, we compared the GST and N-GST buffer layers. We believe that doped nitrogen helped to control Cu-ion injection into the resistive switching layer, and to confine the joule heating during the reset process, enabling a high on/off ratio and improved switching uniformity.

In this paper, the effect of the titanium oxide-based tunnel barrier on the non-linearity and switching uniformity of resistive random access memory has been investigated with the object of achieving excellent device non-linearity and reliability for cross-point array applications. To form the tunnel barrier of titanium oxide, its thickness was engineered using the deposition time. The tunnel barrier effectively controls the current flow in the devices with a tunneling mechanism that modifies the tunnel barrier thickness for non-linearity and switching reliability of devices. The tunnel barrier controls the current behavior of the device because most of the bias is applied to the tunnel barrier owing to its dominant resistance state. In addition, the tunnel barrier can exhibit uniform resistive switching during the set operation with the controlled current flow.

A 3D high-density switching device is realized utilizing titanium oxide, which is the most optimum material, but which is not practically demonstrated yet. The 1S1R (one ReRAM with the developed switching device) exhibits memory characteristics with a significantly suppressed sneak current, which can be used to realize high-density ReRAM applications.