Explosive phenomena such as supernova remnant shocks and solar flares have demonstrated evidence for the production of relativistic particles. Interest has therefore been renewed in collisionless ...shock waves and magnetic reconnection as a means to achieve such energies. Although ions can be energized during such phenomena, the relativistic energy of the electrons remains a puzzle for theory. We present supercomputer simulations showing that efficient electron energization can occur during turbulent magnetic reconnection arising from a strong collisionless shock. Upstream electrons undergo first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. These results shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves.
We show that the Weibel-mediated collisionless shocks are driven at nonrelativistic propagation speed (**0.1e < V < 0.45c) in unmagnetized electron-ion plasmas by performing two-dimensional ...particle-in-cell simulations. It is shown that the profiles of the number density and the mean velocity in the vicinity of the shock transition region, which are normalized by the respective upstream values, are almost independent of the upstream bulk velocity, i.e., the shock velocity. In particular, the width of the shock transition region is similar to 100 ion inertial lengths, independent of the shock velocity. For these shocks the energy density of the magnetic field generated by the Weibel-type instability within the shock transition region reaches typically 1%-2% of the upstream bulk kinetic energy density. This mechanism probably explains the robust formation of collisionless shocks, for example, driven by young supernova remnants, with no assumption of an external magnetic field in the universe.
Abstract Post-traumatic stress disorder (PTSD) is a stress-related mental disorder caused by traumatic experience, and presents with characteristic symptoms, such as intrusive memories, a state of ...hyperarousal, and avoidance, that endure for years. Single-prolonged stress (SPS) is one of the animal models proposed for PTSD. Rats exposed to SPS showed enhanced inhibition of the hypothalamo-pituitary–adrenal (HPA) axis, which has been reliably reproduced in patients with PTSD, and increased expression of glucocorticoid receptor (GR) in the hippocampus. In this study, we characterized further neuroendocrinologic, behavioral and electrophysiological alterations in SPS rats. Plasma corticosterone recovered from an initial increase within a week, and gross histological changes and neuronal cell death were not observed in the hippocampus of the SPS rats. Behavioral analyses revealed that the SPS rats presented enhanced acoustic startle and impaired spatial memory that paralleled the deficits in hippocampal long-term potentiation (LTP) and depression. Contextual fear memory was enhanced in the rats 1 week after SPS exposure, whereas LTP in the amygdala was blunted. Interestingly, blockade of GR activation by administering 17-beta-hydroxy-11-beta-/4-/methyl-1-methylethylaminophenyl/-17-alpha-prop-1-ynylestra-4-9-diene-3-one (RU40555), a GR antagonist, prior to SPS exposure prevented potentiation of fear conditioning and impairment of LTP in the CA1 region. Altogether, SPS caused a number of behavioral changes similar to those described in PTSD, which marks SPS as a putative PTSD model. The preventive effects of a GR antagonist suggested that GR activation might play a critical role in producing the altered behavior and neuronal function of SPS rats.
Gemcitabine plus cisplatin (GC) is the standard treatment of advanced biliary tract cancer (BTC); however, it causes nausea, vomiting, and anorexia, and requires hydration. Gemcitabine plus S-1 (GS) ...reportedly has equal to, or better, efficacy and an acceptable toxicity profile. We aimed to confirm the non-inferiority of GS to GC for patients with advanced/recurrent BTC in terms of overall survival (OS).
We undertook a phase III randomized trial in 33 institutions in Japan. Eligibility criteria included chemotherapy-naïve patients with recurrent or unresectable BTC, an Eastern Cooperative Oncology Group Performance Status of 0−1, and adequate organ function. The calculated sample size was 350 with a one-sided α of 5%, a power of 80%, and non-inferiority margin hazard ratio (HR) of 1.155. The primary end point was OS, while the secondary end points included progression-free survival (PFS), response rate (RR), adverse events (AEs), and clinically significant AEs defined as grade ≥2 fatigue, anorexia, nausea, vomiting, oral mucositis, or diarrhea.
Between May 2013 and March 2016, 354 patients were enrolled. GS was found to be non-inferior to GC median OS: 13.4months with GC and 15.1months with GS, HR, 0.945; 90% confidence interval (CI), 0.78–1.15; P=0.046 for non-inferiority. The median PFS was 5.8months with GC and 6.8months with GS (HR 0.86; 95% CI 0.70–1.07). The RR was 32.4% with GC and 29.8% with GS. Both treatments were generally well-tolerated. Clinically significant AEs were observed in 35.1% of patients in the GC arm and 29.9% in the GS arm.
GS, which does not require hydration, should be considered a new, convenient standard of care option for patients with advanced/recurrent BTC.
This trial has been registered with the UMIN Clinical Trials Registry (http://www.umin.ac.jp/ctr/index.htm), number UMIN000010667.
The time evolution and saturation of the Weibel instability at the ion Alfvén current are presented by ab initio particle-in-cell (PIC) simulations. We found that the ion Weibel current in ...three-dimensional (3D) simulations could evolve into the Alfvén current where the magnetic field energy is sustained at 1.5% of the initial beam kinetic energy. The current filaments are no longer isolated at saturation, but rather connected to each other to form a network structure. Electrons are continuously heated during the coalescence of the filaments, which is crucial for obtaining sustained magnetic fields with much stronger levels than with two-dimensional (2D) simulations. The results highlight again the importance of the Weibel instability in generating magnetic fields in laboratory, astrophysical, and cosmological situations.
Smart grid (SG) communication has recently received significant attentions to facilitate intelligent and distributed electric power transmission systems. However, communication trust and security ...issues still present practical concerns to the deployment of SG. In this paper, to cope with these challenging concerns, we propose a lightweight message authentication scheme features as a basic yet crucial component for secure SG communication framework. Specifically, in the proposed scheme, the smart meters which are distributed at different hierarchical networks of the SG can first achieve mutual authentication and establish the shared session key with Diffie-Hellman exchange protocol. Then, with the shared session key between smart meters and hash-based authentication code technique, the subsequent messages can be authenticated in a lightweight way. Detailed security analysis shows that the proposed scheme can satisfy the desirable security requirements of SG communications. In addition, extensive simulations have also been conducted to demonstrate the effectiveness of the proposed scheme in terms of low latency and few signal message exchanges.
Analog molecular circuits can exploit the nonlinear nature of biochemical reaction networks to compute low-precision outputs with fewer resources than digital circuits. This analog computation is ...similar to that employed by gene-regulation networks. Although digital systems have a tractable link between structure and function, the nonlinear and continuous nature of analog circuits yields an intricate functional landscape, which makes their design counter-intuitive, their characterization laborious and their analysis delicate. Here, using droplet-based microfluidics, we map with high resolution and dimensionality the bifurcation diagrams of two synthetic, out-of-equilibrium and nonlinear programs: a bistable DNA switch and a predator-prey DNA oscillator. The diagrams delineate where function is optimal, dynamics bifurcates and models fail. Inverse problem solving on these large-scale data sets indicates interference from enzymatic coupling. Additionally, data mining exposes the presence of rare, stochastically bursting oscillators near deterministic bifurcations.
There are numerous research challenges that need to be addressed until a wide deployment of vehicular ad hoc networks (VANETs) becomes possible. One of the critical issues consists of the design of ...scalable routing algorithms that are robust to frequent path disruptions caused by vehicles' mobility. This paper argues the use of information on vehicles' movement information (e.g., position, direction, speed, and digital mapping of roads) to predict a possible link-breakage event prior to its occurrence. Vehicles are grouped according to their velocity vectors. This kind of grouping ensures that vehicles, belonging to the same group, are more likely to establish stable single and multihop paths as they are moving together. Setting up routes that involve only vehicles from the same group guarantees a high level of stable communication in VANETs. The scheme presented in this paper also reduces the overall traffic in highly mobile VANET networks. The frequency of flood requests is reduced by elongating the link duration of the selected paths. To prevent broadcast storms that may be intrigued during path discovery operation, another scheme is also introduced. The basic concept behind the proposed scheme is to broadcast only specific and well-defined packets, referred to as ldquobest packetsrdquo in this paper. The performance of the scheme is evaluated through computer simulations. Simulation results indicate the benefits of the proposed routing strategy in terms of increasing link duration, reducing the number of link-breakage events and increasing the end-to-end throughput.
A two-dimensional particle-in-cell simulation is performed to investigate weakly magnetized perpendicular shocks with a magnetization parameter of {sigma} = 6 x 10{sup -5}, which is equivalent to a ...high Alfven Mach number M{sub A} of {approx}130. It is shown that current filaments form in the foot region of the shock due to the ion-beam-Weibel instability (or the ion filamentation instability) and that they generate a strong magnetic field there. In the downstream region, these current filaments also generate a tangled magnetic field that is typically 15 times stronger than the upstream magnetic field. The thermal energies of electrons and ions in the downstream region are not in equipartition and their temperature ratio is T{sub e}/T{sub i} {approx} 0.3-0.4. Efficient electron acceleration was not observed in our simulation, although a fraction of the ions are accelerated slightly on reflection at the shock. The simulation results agree very well with the Rankine-Hugoniot relations. It is also shown that electrons and ions are heated in the foot region by the Buneman instability (for electrons) and the ion-acoustic instability (for both electrons and ions). However, the growth rate of the Buneman instability is significantly reduced due to the relatively high temperature of the reflected ions. For the same reason, ion-ion streaming instability does not grow in the foot region.
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