Anonymizing continuous queries with delay-tolerant mix-zones over road networks

This paper presents a delay-tolerant mix-zone framework for protecting the location privacy of mobile users against continuous query correlation attacks. First, we describe and analyze the continuous query correlation attacks (CQ-attacks) that perform query correlation based inference to break the anonymity of road network-aware mix-zones. We formally study the privacy strengths of the mix-zone anonymization under the CQ-attack model and argue that spatial cloaking or temporal cloaking over road network mix-zones is ineffective and susceptible to attacks that carry out inference by combining query correlation with timing correlation (CQ-timing attack) and transition correlation (CQ-transition attack) information. Next, we introduce three types of delay-tolerant road network mix-zones (i.e.; temporal, spatial and spatio-temporal) that are free from CQ-timing and CQ-transition attacks and in contrast to conventional mix-zones, perform a combination of both location mixing and identity mixing of spatially and temporally perturbed user locations to achieve stronger anonymity under the CQ-attack model. We show that by combining temporal and spatial delay-tolerant mix-zones, we can obtain the strongest anonymity for continuous queries while making acceptable tradeoff between anonymous query processing cost and temporal delay incurred in anonymous query processing. We evaluate the proposed techniques through extensive experiments conducted on realistic traces produced by GTMobiSim on different scales of geographic maps. Our experiments show that the proposed techniques offer high level of anonymity and attack resilience to continuous queries. © 2013 Springer Science+Business Media New York

Superconductivity in Li8Au electride

Located at crystal voids, interstitial anion electrons (IAEs) have diverse topologies, which may be tuned to achieve new properties. Elucidating the role of IAEs in electron-phonon coupling (EPC), and using it to design new electride superconductors, leads to the current prediction of superconducting Li8Au at high pressure. We suggest that the occurence of high-temperature superconductivity in electrides requires high-symmetry structures with hydrogen-like cages, an electron acceptor element to balance charges, and isolated IAEs coupled with medium-frequency vibrations. The uniquely designed Li8Au electride has a NaCl-type (B1) lattice, with atomic Au and cubic Li8 cages as bases. Isolated IAEs are formed at the cage centers, with extra charges taken up by Au. These octahedrally coordinated IAEs have a p-orbital-like attribute and are strongly coupled with atomic vibrations in the Li8 cages. The strong EPC in Li8Au results in a calculated Tc of 73.1 K at 250 GPa, which is the highest Tc reported to date for all the electrides. A slight substitutional Pt doping can enhance the Tc of Li8Au to exceed liquid nitrogen temperature.Comment: 7 Pages, 3 Figure

Effect of natural polymer materials on skin healing based on internal wound microenvironment: a review

The concept of wound microenvironment has been discussed for a long time. However, the mechanism of the internal microenvironment is relatively little studied. Here, we present a systematic discussion on the mechanism of natural polymer materials such as chitosan, cellulose, collagen and hyaluronic acid through their effects on the internal wound microenvironment and regulation of wound healing, in order to more comprehensively explain the concept of wound microenvironment and provide a reference for further innovative clinical for the preparation and application of wound healing agents

Large-scale solar district heating plants in Danish smart thermal grid: developments and recent trends

Large solar collector fields are very popular in district heating system in Denmark, even though the solar radiation source is not favorable at high latitudes compared to many other regions. Business models for large solar heating plants in Denmark has attracted much attention worldwide. Denmark is not only the biggest country in both total installed capacities and numbers of large solar district heating plants, but also is the first and only country with commercial market-driven solar district heating plants. By the end of 2017, more than 1.3 million m2 solar district heating plants are in operation in Denmark. Furthermore, more than 70% of the large solar district heating plants worldwide are constructed in Denmark. Based on the case of Denmark, this study reviews the development of large solar district heating plants in Denmark since 2006. Success factors for Danish experiences was summarized and discussed. Novel design concepts of large solar district heating plants are also addressed to clarify the future development trend. Potential integration of large solar district heating plants with other renewable energy technologies are discussed. This paper can provide references to potential countries that want to exploit the market for solar district heating plants. Policy-makers can evaluate the advantages and disadvantages of solar district heating systems in the national energy planning level based on the know-how and experiences from Denmark

Grid compliance for the land based electrical power generators

The fault ride-through (FRT) or low voltage ride-through (LVRT) is one of the critical requirements in the grid codes or distribution codes. The codes are normally defined by the grid operators or the local authority, and generators connecting to a grid are required to comply with all the relevant requirements stated in the code. The LVRT requirement was initially established and applied to wind power generators connecting to power grids. But it is now applied to all generators in many recent revised codes regardless of the technologies used. Complying with the LVRT requirement is very challenging for distributed synchronous generators due to the rotor angle stability during fault transients. Many ways and means for LVRT capability enhancement have been researched for wind generators, but only limited researches have been conducted for LVRT capability enhancement for distributed synchronous generators. This work is focused on developing topologies and control strategies for LVRT capability enhancements for engine synchronous generators, an example of distribution synchronous generators (DSG). A topology with the switched-in series-controlled dynamic braking resistors (SSCDBR) is proposed for the LVRT capability enhancement. The SSC-DBR is connected in series with the neutral ends of the star-configured windings of the unit transformer. In steady state, the DBR is bypassed by a mechanical circuit breaker and no power loss is expected. When a severe grid fault is detected, the DBR is switched-in to consume the excessive energy from the generators. Along with the proposed configuration of the SSC-DBR, a control strategy is developed to make the topology effective. The controller is designed so that the SSC-DBR is activated only when the fault voltage is below the predetermined value and the fault duration is longer than the preset time for two-phase and three-phase faults. The proposed SSC-DBR configuration largely reduces the fault current flowing through the power semiconductor switches resulting a reduction on the rating and cost and an enhancement on the reliability of the approach. The proposed control strategy reduces the unnecessary activation of the DBR thus further increases the life-time and reliability of the proposed solution. Furthermore, the inherent dynamic performer of the synchronous generator is maintained for none critical grid faults. An alternative configuration of the SSC-DBR with the delta-configured winding of the unit transformer is proposed as well. Simulation studies are carried out to evaluate the performances of the proposed approach with various scenarios. The simulation results show that the proposed method is able to enhance the LVRT capability of the modeled engine generator to comply one of the most stringent LVRT capability requirement. Finally the effectiveness and performance are validated by a down-scaled prototype in the laboratory. In Addition, two approaches for rotor angle estimation and measurement are proposed in this work. Rotor angle measurement and out-of-synchronism (OOS) protection are normally not required and equipped for DSG. Under a grid disturbance, when the LVRT capability requirement is implemented, an OOS may occurs in the event of LVRT solution failure. Thus it is a need to protect and trip DSG when the DSG is in OOS condition. Other than the conventional OOS protection relay, the estimated angle between the rotor and the grid voltage can also be used to determine the OOS condition. A holistic approach, which compute the rotor angle in steady state and transient differently, is proposed. In steady state, the rotor angle is computer using the static machine parameters and the measured quantities. While the change of the rotor angle and the pre-fault steady state rotor angle are combined to obtained the rotor angle in a fault transient. Simulation study is conducted and the results show that the proposed method is able to the estimate the rotor angle in steady state and transient periods. Another proposed method is using a permanent magnet synchronous signaling generator (PMSSG) for rotor angle estimation and measurement. A PMSSG is attached to the shaft of the rotor and a voltage signal that reflects the internal rotor position is produced at the terminal of the PMSSG. The rotor angle of the power generator is then estimated based on voltage at the PCC and from the PMSSG terminal. A digital signal processor is used for computing the rotor angle in transient conditions.Doctor of Philosoph

Grid compliance for gas turbine power generation

Due to their low greenhouse gases emission, high efficiency and the availability of fuel gas, gas turbine powered generations have become one of most popular electricity generation systems. In this connection, a computer-based simulation model of gas turbine is most necessary when it comes to the study the dynamics of gas turbine system. For this purpose, the model proposed by Rowen is the most commonly used. However, it is not readily available in MATLAB software. This thesis presents the construction and validation of Rowen’s model under the Matlab/Simulink platform. Open-loop tests, closed-loop tests are conducted, and simulation results are presented and discussed. A three phase ground fault is simulated to observe the performance of a specific gas turbine, and the simulation results are compared with those obtained from field-tests. The two sets of results appear to agree amicably well.Master of Science (Power Engineering

Insight into Seasonal Change of Phytochemicals, Antioxidant, and Anti-Aging Activities of Root Bark of Paeonia suffruticosa (Cortex Moutan) Combined with Multivariate Statistical Analysis

Chemical compositions, antioxidants, and anti-aging activities of Cortex Moutan (CM), from different collection periods and different producing areas, were measured and compared in order to obtain excellent CM extracts. The bioactivities of CM extracts were examined by an in vitro antioxidant method and a UVB irradiated human dermal fibroblast (HDF) model. Phytochemical properties were obtained from ultra-fast liquid chromatography quadrupole time-of-flight mass spectrometry (UFLC-Q-TOF-MS) prior to the multivariate statistical analysis. As for the results, the extracts of Heze CM (HZCM) and Luoyang CM (LYCM) collected in June had better in vitro antioxidant activities, significantly increased the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and reduced the content of malondialdehyde (MDA), compared to other CM extracts. HZCM and LYCM extracts could upregulate the relative expression of SOD and GSH-Px mRNA. The extract of HZCM collected in June could significantly repress the production of matrix metalloproteinase 1 (MMP-1) and improve the production of procollagen type I (PCOL)-I in UVB irradiated HDF. In total, 50 compounds, including 17 monoterpenoids, 19 flavonoids, 13 phenols, and 1 amino acid were identified or tentatively identified in the CM extracts. Gallic acid, p-hydroxybenzoic acid, oxypaeoniflorin, paeoniflorin, 1,2,3,4,6-O-pentagalloyl glucose, and paeonol were predominant compounds in the CM extracts. Taken together, CM collected from April to September had better antioxidant and anti-aging effects for external usage

Super-lift converter multilevel DC/AC inverters used in solar panel energy systems

This project presents design, simulation and hardware implementation of super-lift converter multilevel inverter. In order to maintain the output voltage at a constant level, the closed-loop control system was used with PI controller. With proper tuned PI controller, the Super-Lift converter was able to achieve the design specifications. In the multilevel inverter design, the zener diodes were used to divide the DC voltage from super-lift converter into several levels with equal voltage; with carefully designed switching circuit, the different voltage level was apply to the load at different timing with different duration. A microcontroller AN89S8253 was used for the switching signal design and the program code was written in C. The results of software simulation and hardware implementation for super-lift converter multilevel inverter are presented.Bachelor of Engineerin