Adaptive variable-grid least-squares reverse-time migration

Variable-grid methods have the potential to save computing costs and memory requirements in forward modeling and least-squares reverse-time migration (LSRTM). However, due to the inherent difficulty of automatic grid discretization, conventional variable-grid methods have not been widely used in industrial production. We propose a variable-grid LSRTM (VG-LSRTM) method based on an adaptive sampling strategy to improve computing efficiency and reduce memory requirements. Based on the mapping relation of two coordinate systems, we derive variable-grid acoustic wave equation and its corresponding Born forward modeling equation. On this basis, we develop a complete VG-LSRTM framework. Numerical experiments on a layered model validate the feasibility of the proposed VG-LSRTM algorithm. LSRTM tests on a modified Marmousi model demonstrate that our method can save computational costs and memory requirements with little accuracy loss

The YPLGVG sequence of the Nipah virus matrix protein is required for budding

<p>Abstract</p> <p>Background</p> <p><it>Nipah virus </it>(NiV) is a recently emerged paramyxovirus capable of causing fatal disease in a broad range of mammalian hosts, including humans. Together with <it>Hendra virus </it>(HeV), they comprise the genus <it>Henipavirus </it>in the family <it>Paramyxoviridae</it>. Recombinant expression systems have played a crucial role in studying the cell biology of these Biosafety Level-4 restricted viruses. <it>Henipavirus </it>assembly and budding occurs at the plasma membrane, although the details of this process remain poorly understood. Multivesicular body (MVB) proteins have been found to play a role in the budding of several enveloped viruses, including some paramyxoviruses, and the recruitment of MVB proteins by viral proteins possessing late budding domains (L-domains) has become an important concept in the viral budding process. Previously we developed a system for producing NiV virus-like particles (VLPs) and demonstrated that the matrix (M) protein possessed an intrinsic budding ability and played a major role in assembly. Here, we have used this system to further explore the budding process by analyzing elements within the M protein that are critical for particle release.</p> <p>Results</p> <p>Using rationally targeted site-directed mutagenesis we show that a NiV M sequence YPLGVG is required for M budding and that mutation or deletion of the sequence abrogates budding ability. Replacement of the native and overlapping Ebola VP40 L-domains with the NiV sequence failed to rescue VP40 budding; however, it did induce the cellular morphology of extensive filamentous projection consistent with wild-type VP40-expressing cells. Cells expressing wild-type NiV M also displayed this morphology, which was dependent on the YPLGVG sequence, and deletion of the sequence also resulted in nuclear localization of M. Dominant-negative VPS4 proteins had no effect on NiV M budding, suggesting that unlike other viruses such as Ebola, NiV M accomplishes budding independent of MVB cellular proteins.</p> <p>Conclusion</p> <p>These data indicate that the YPLGVG motif within the NiV M protein plays an important role in M budding; however, involvement of any specific components of the cellular MVB sorting pathway in henipavirus budding remains to be demonstrated. Further investigation of henipavirus assembly and budding may yet reveal a novel mechanism(s) of viral assembly and release that could be applicable to other enveloped viruses or have therapeutic implications.</p

Small-Molecule Probes Targeting the Viral PPxY-Host Nedd4 Interface Block Egress of a Broad Range of RNA Viruses.

Budding of filoviruses, arenaviruses, and rhabdoviruses is facilitated by subversion of host proteins, such as Nedd4 E3 ubiquitin ligase, by viral PPxY late (L) budding domains expressed within the matrix proteins of these RNA viruses. As L domains are important for budding and are highly conserved in a wide array of RNA viruses, they represent potential broad-spectrum targets for the development of antiviral drugs. To identify potential competitive blockers, we used the known Nedd4 WW domain-PPxY interaction interface as the basis of an in silico screen. Using PPxY-dependent budding of Marburg (MARV) VP40 virus-like particles (VLPs) as our model system, we identified small-molecule hit 1 that inhibited Nedd4-PPxY interaction and PPxY-dependent budding. This lead candidate was subsequently improved with additional structure-activity relationship (SAR) analog testing which enhanced antibudding activity into the nanomolar range. Current lead compounds 4 and 5 exhibit on-target effects by specifically blocking the MARV VP40 PPxY-host Nedd4 interaction and subsequent PPxY-dependent egress of MARV VP40 VLPs. In addition, lead compounds 4 and 5 exhibited antibudding activity against Ebola and Lassa fever VLPs, as well as vesicular stomatitis and rabies viruses (VSV and RABV, respectively). These data provide target validation and suggest that inhibition of the PPxY-Nedd4 interaction can serve as the basis for the development of a novel class of broad-spectrum, host-oriented antivirals targeting viruses that depend on a functional PPxY L domain for efficient egress. IMPORTANCE: There is an urgent and unmet need for the development of safe and effective therapeutics against biodefense and high-priority pathogens, including filoviruses (Ebola and Marburg) and arenaviruses (e.g., Lassa and Junin) which cause severe hemorrhagic fever syndromes with high mortality rates. We along with others have established that efficient budding of filoviruses, arenaviruses, and other viruses is critically dependent on the subversion of host proteins. As disruption of virus budding would prevent virus dissemination, identification of small-molecule compounds that block these critical viral-host interactions should effectively block disease progression and transmission. Our findings provide validation for targeting these virus-host interactions as we have identified lead inhibitors with broad-spectrum antiviral activity. In addition, such inhibitors might prove useful for newly emerging RNA viruses for which no therapeutics would be available

Interferon Impedes an Early Step of Hepatitis Delta Virus Infection

Hepatitis delta virus (HDV) infects hepatocytes, the major cell type of the liver. Infection of the liver may be either transient or chronic. The prognosis for patients with chronic HDV infection is poor, with a high risk of cirrhosis and hepatocellular carcinoma. The best antiviral therapy is weekly administration for at least one year of high doses of interferon alpha. This efficacy of interferon therapy has been puzzling in that HDV replication in transfected cell lines is reported as insensitive to administration of interferon alpha or gamma. Similarly, this study shows that even when an interferon response was induced by transfection of poly(IC) into a cell line, HDV RNA accumulation was only modestly inhibited. However, when the HDV replication was initiated by infection of primary human hepatocytes, simultaneous addition of interferons alpha or gamma at 600 units/ml, a concentration comparable to that achieved in treated patients, the subsequent HDV RNA accumulation was inhibited by at least 80%. These interferon treatments were shown to produce significant time-dependent increases of host response proteins such as for Stat-1, phosphoStat-1, Mx1/2/3 and PKR, and yet interferon pretreatment of hepatocytes did not confer an increased inhibition of HDV replication over interferon treatment at the time of (or after) infection. These and other data support the interpretation that interferon action against HDV replication can occur and is largely mediated at the level of entry into primary human hepatocytes. Thus in vivo, the success of long-term interferon therapy for chronic HDV, may likewise involve blocking HDV spread by interfering with the initiation of productive infection of naïve hepatocytes

Distributed voltage unbalance compensation for an islanded microgrid system in a sensitive load bus

This project demonstrated a distributed voltage unbalance compensation scheme for an islanded microgrid system with main consideration of a sensitive load bus. A hierarchical control structure is commonly used for voltage unbalance compensation. Realization of voltage unbalance compensation in this project is to propose a cooperative and distributed compensation strategy. A two-layer secondary compensation controller is designed for each local Distributed Generator (DG). It consists of a communication layer and a compensator layer, as well as a new concept of Contribution Level is introduced to illustrate the compensation ability for a certain DG. A cooperatively distributed secondary control requiring information sharing is proposed based on the finite-time average consensus algorithm and a graph detection algorithm. The algorithms applied can fulfill the compensation within finite time and execute information sharing without knowing the structure as prior. The distributed secondary compensation is able to perform the similar compensation ability as centralized secondary structure; meanwhile, there are also improvement for special conditions including communication fault and plug-and-play. Simulations are carried out in Matlab Simulink environment, and cases involving communication failure, CL shift, and DG plug-out are tested and analyzed to verify the practicability of proposed design.Bachelor of Engineerin