Model-Based Cyber-Security Framework for Nuclear Power Plant

A model-based cyber-security framework has been developed to address the new challenges of cyber threats due to the increasing implementation of digital components in the instrumentation and control (I&C) system of modern nuclear power plants. The framework is developed to detect intrusions to pressurized water reactor (PWR) systems that could result in unnecessary reactor shutdown events due to out-of-range water levels of steam generators. The generation of potential attack scenarios demonstrated a process for identifying the most susceptible attack pathways and components in the I&C system. It starts with identifying two key I&C divisions of the modern AP1000 design related to the reactor trip functions, protection and safety monitoring system, and plant control system. The attack tree analysis is performed on the steam generator (SG) water level control system using the SAPHIRE 8.0.9 code. To quantify the system susceptibility to cyber-attack events, causing reactor trips, we propose sensitivity metrics to identify the low-order sets of components that may be compromised and the degree of perturbations needed for each component. The multi-path event tree (MPET) structures are developed to efficiently and intuitively display a large number of dominant or risk-significant attack scenarios instead of the traditional event trees representing minimal cut sets. A reduced order model (ROM) has been developed to efficiently represent the SG dynamics and facilitate the detection of potential cyber-attacks. The dynamic ROM is built on the energy balance equation for a single vertical boiling channel approximating a U-tube steam generator. The ROM provides an essential relationship connecting the reactor power, water level, and feedwater flow rate. An application programming interface (API) for the I&C systems serving as the interface between the RELAP5 system code and the ROM has been developed. A Kalman filtering based detection method has been proposed, providing optimal tracking of SG water level combining the uncertain simulation results with the observation data subject to statistical fluctuations. An observed plant state with significant deviation from the optimal system projection could then indicate potential intrusions into the system. Finally, a mitigation strategy considering the controller feedback is proposed to avoid the reactor trip due to attack on SG water level sensors. The worst-case attack within this issue space is defined, and the maximum delay time allowed for the mitigation is obtained.PHDNuclear Engineering & Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162955/1/gjunjie_1.pd

Sneutrino DM in the NMSSM with inverse seesaw mechanism

In supersymmetric theories like the Next-to-Minimal Supersymmetric Standard Model (NMSSM), the lightest neutralino with bino or singlino as its dominant component is customarily taken as dark matter (DM) candidate. Since light Higgsinos favored by naturalness can strength the couplings of the DM and thus enhance the DM-nucleon scattering rate, the tension between naturalness and DM direct detection results becomes more and more acute with the improved experimental sensitivity. In this work, we extend the NMSSM by inverse seesaw mechanism to generate neutrino mass, and show that in certain parameter space the lightest sneutrino may act as a viable DM candidate, i.e. it can annihilate by multi-channels to get correct relic density and meanwhile satisfy all experimental constraints. The most striking feature of the extension is that the DM-nucleon scattering rate can be naturally below its current experimental bounds regardless of the higgsino mass, and hence it alleviates the tension between naturalness and DM experiments. Other interesting features include that the Higgs phenomenology becomes much richer than that of the original NMSSM due to the relaxed constraints from DM physics and also due to the presence of extra neutrinos, and that the signatures of sparticles at colliders are quite different from those with neutralino as DM candidate.Comment: 33 page

RNA G-quadruplexes are globally unfolded in eukaryotic cells and depleted in bacteria

INTRODUCTION: Many cellular RNAs contain regions that fold into stable structures required for function. Both Watson−Crick and noncanonical interactions can play important roles in forming these structures. An intriguing noncanonical structure is the RNA G-quadruplex (RG4), a four-stranded structure containing two or more layers of G-quartets, in which the Watson–Crick face of each of four G residues pairs to the Hoogsteen face of the neighboring G residues. RG4 regions can be very stable in vitro, particularly in the presence of K+, and thus they are generally assumed to be predominantly folded within cells, which have ample K+. Indeed, these structures have been implicated in mRNA processing and translation, with recently proposed roles in cancer and other human diseases. However, the number of cellular RNAs that can fold into RG4 structures has been unclear, as has been the extent to which these RG4 regions are folded in cells. RATIONALE: Enzymes and chemicals that act on RNA with structure-dependent preferences provide valuable tools for detecting and monitoring RNA folding. For example, dimethyl sulfate (DMS) treatment of RNA, either in vitro or in cells, coupled with high-throughput sequencing of abortive primer-extension products can monitor the folding states of many RNAs in one experiment. Analogous high-throughput methods use cell-permeable variants of SHAPE (selective 2′-hydroxyl acylation analyzed by primer extension) reagents. These methods reveal important differences between RNA structures formed in vivo and those formed in vitro. However, they are designed to detect Watson−Crick pairing and thus do not identify RG4 structures or provide information on their folding states. After recognizing that RG4 regions can block reverse transcriptase, we reasoned that this property, together with the known ability of RG4s to protect the N7 of participating G nucleotides from DMS modification, could be used to develop a suite of high-throughput methods to both identify endogenous RNAs that can fold into RG4s in vitro and determine whether these regions also fold in cells. RESULTS: We first developed a high-throughput method that identifies RG4 regions on the basis of their propensity to stall reverse transcriptase in a K+-dependent manner. Applying this method to RNA from mammalian cell lines and yeast, we identified >10,000 endogenous regions that form RG4s in vitro, thereby expanding by a factor of >100 the catalog of endogenous regions with experimentally supported propensity to fold into RG4 structures. To infer the folding state of these RG4 regions in vitro and in cells, DMS treatment was performed before profiling of reverse-transcriptase stops. These analyses showed that, in contrast to previous assumptions, regions that folded into RG4 structures in vitro were overwhelmingly unfolded in vivo, as indicated by their accessibility to DMS modification in cells. A complementary probing strategy using a SHAPE reagent confirmed the unfolded state of most RG4 regions in eukaryotic cells. Moreover, RG4 regions remained unfolded both in cells depleted of adenosine 5′-triphosphate and in cells lacking a helicase known to unfold RG4 regions in vitro. Applying our probing methods to bacteria revealed a different behavior, in that model RG4 regions that were unfolded in eukaryotic cells were folded when expressed in Escherichia coli. However, these ectopically expressed quadruplexes impaired mRNA translation and cell growth, which helps explain why very few endogenous sequences that could fold into RG4s were detected in the transcriptomes of E. coli and the two other eubacteria analyzed. CONCLUSION: In mammals, thousands of endogenous RNA sequences have regions that can fold into RG4s in vitro, but these regions are globally unfolded in eukaryotic cells, presumably by robust and effective machinery that remains to be fully characterized. In contrast, RG4 regions are permitted to fold in E. coli cells, but E. coli and other bacteria have undergone evolutionary depletion of endogenous RG4-forming sequences

A dual-grating InGaAsP/InP DFB laser integrated with an SOA for THz generation

We report a dual-mode semiconductor laser that has two gratings with different periods below and above the active layer. A semiconductor optical amplifier (SOA), which is integrated with the dual-mode laser, plays an important role in balancing the optical power and reducing the linewidths of the emission modes. A stable two mode emission with the 13.92-nm spacing can be obtained over a wide range of distributed feedback and SOA injection currents. Compared with other types of dual-mode lasers, our device has the advantages of simple structure, compact size, and low fabrication cost

Multi-agent Coordination Under Temporal Logic Tasks and Team-Wise Intermittent Communication

Multi-agent systems outperform single agent in complex collaborative tasks. However, in large-scale scenarios, ensuring timely information exchange during decentralized task execution remains a challenge. This work presents an online decentralized coordination scheme for multi-agent systems under complex local tasks and intermittent communication constraints. Unlike existing strategies that enforce all-time or intermittent connectivity, our approach allows agents to join or leave communication networks at aperiodic intervals, as deemed optimal by their online task execution. This scheme concurrently determines local plans and refines the communication strategy, i.e., where and when to communicate as a team. A decentralized potential game is modeled among agents, for which a Nash equilibrium is generated iteratively through online local search. It guarantees local task completion and intermittent communication constraints. Extensive numerical simulations are conducted against several strong baselines.Comment: 6 pages, 2 figure