No abstract

As a three-dimensional topological insulator (TI), bismuth telluride (Bi2Te3) has two-dimensional electron gas on its surface where negative quantum capacitance (NQC) can exist at a specific biasing condition. In order to experimentally confirm NQC in a TI, a metal–insulator–semiconductor (MIS) capacitor (i.e., metal–Bi2Te3–SiO2–silicon) is fabricated. The capacitance–voltage measurement of the MIS capacitor at 300 K shows that as the depletion capacitance in silicon decreases, the total capacitance of the MIS capacitor, which consists of two capacitors connected in series (i.e., insulator capacitor and depletion capacitor), increases in the depletion region at a frequency of 50 kHz. The amplified capacitance indicates the existence of NQC on the surface of the TI, and it originates from the strongly correlated electron system. The NQC of the TI opens avenues for sub-60-mV/decade steep switching silicon devices.

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In order to identify the relation between revenue water (RW) ratio and key local factors in a quantifiable way, 90 effect factors were considered as regional characteristics for 79 Korean cities. Seven statistically significant effect factors were chosen through correlation analysis. Three principal components independently influencing RW ratio were extracted by principal component analysis (PCA). The 79 cities were grouped into six clusters by k-means clustering (KMC) of the factor scores of the cities. Then key local factors were identified and their impacts were quantified by multiple regression analysis (MRA) and they were justified by T-test and F-test. The approach through correlation-PCA-KMC-MRA was proved to be one of scientific ways for identification of key local factors. According to the result, it was suggested that a shorter length of distribution system, a water supply with smaller number of bigger customer meters a and gravitational supply through reservoir would be advantageous from a RW ratio's point of view.

In case of Seoul city in Korea, the level of water leakage from any distribution system is evaluated by comparison of measured minimum night flows (NFMs) with a fixed allowable leakage level. However, infrastructure condition of District Metered Areas (DMAs) could be misjudged, because characteristics of the system are not considered properly. Therefore the components of NFM were estimated in residential and business DMAs by using data of night uses collected by modified option A test and real losses from water balance analysis. A new background minimum night flow equation was developed by the components of NFM. Applicability of the equation was tested on various revenue water % residential and business DMAs. As a result, it is concluded that the new background night flow developed in this study is more reasonable in Korea and could be used to judge whether the DMAs have economically recoverable unreported bursts prior to leakage detection activity.