AMPTE/CCE‐SCATHA simultaneous observations of substorm‐associated magnetic fluctuations

This study examines substorm-associated magnetic field fluctuations observed by the AMPTE/CCE and SCATHA satellites in the near-Earth tail. Three tail reconfiguration events are selected, one event on August 28, 1986, and two consecutive events on August 30, 1986. The fractal analysis was applied to magnetic field measurements of each satellite. The result indicates that (1) the amplitude of the fluctuation of the north-south magnetic component is larger, though not overwhelmingly, than the amplitudes of the other two components and (2) the magnetic fluctuations do have a characteristic timescale, which is several times the proton gyroperiod. In the examined events the satellite separation was less than 10 times the proton gyroradius. Nevertheless, the comparison between the AMPTE/CCE and SCATHA observations indicates that (3) there was a noticeable time delay between the onsets of the magnetic fluctuations at the two satellite positions, which is too long to ascribe to the propagation of a fast magnetosonic wave, and (4) the coherence of the magnetic fluctuations was low in the August 28, 1986, event and the fluctuations had different characteristic timescales in the first event of August 30, 1986, whereas some similarities can be found for the second event of August 30, 1986. Result 1 indicates that perturbation electric currents associated with the magnetic fluctuations tend to flow parallel to the tail current sheet and are presumably related to the reduction of the tail current intensity. Results 2 and 3 suggest that the excitation of the magnetic fluctuations and therefore the trigger of the tail current disruption is a kinetic process in which ions play an important role. It is inferred from results 3 and 4 that the characteristic spatial scale of the associated instability is of the order of the proton gyroradius or even shorter, and therefore the tail current disruption is described as a system of chaotic filamentary electric currents. However, result 4 suggests that the nature of the tail current disruption can vary from event to event

Hierarchical QoS routing in next generation optical networks

In this paper, we study the problem of inter-domain routing with two additive QoS constraints in hierarchical optical networks. We develop an inter-domain routing protocol that (1) identifies the QoS supported by the paths, (2) selects an inter-domain path that satisfies the QoS requirement of a connection request, and (3) reserves the wavelength on each link along the path in such a way that the number of wavelength converters needed is minimized. Both formal analyses and extensive simulation experiments show that our inter-domain routing protocol outperforms the existing protocols. © 2006 IEEE.published_or_final_versio

Hop-by-hop routing in wireless mesh networks with bandwidth guarantees

Wireless Mesh Network (WMN) has become an important edge network to provide Internet access to remote areas and wireless connections in a metropolitan scale. In this paper, we study the problem of identifying the maximum available bandwidth path, a fundamental issue in supporting quality-of-service in WMNs. Due to interference among links, bandwidth, a well-known bottleneck metric in wired networks, is neither concave nor additive in wireless networks. We propose a new path weight which captures the available path bandwidth information. We formally prove that our hop-by-hop routing protocol based on the new path weight satisfies the consistency and loop-freeness requirements. The consistency property guarantees that each node makes a proper packet forwarding decision, so that a data packet does traverse over the intended path. Our extensive simulation experiments also show that our proposed path weight outperforms existing path metrics in identifying high-throughput paths. © 2012 IEEE.published_or_final_versio

Effect of next-nearest neighbor coupling on the optical spectra in bilayer graphene

We investigate the dependence of the optical conductivity of bilayer graphene (BLG) on the intra- and inter-layer interactions using the most complete model to date. We show that the next nearest-neighbor intralayer coupling introduces new features in the low-energy spectrum that are highly sensitive to sample doping, changing significantly the ``universal'' conductance. Further, its interplay with interlayer couplings leads to an anisotropy in conductance in the ultraviolet range. We propose that experimental measurement of the optical conductivity of intrinsic and doped BLG will provide a good benchmark for the relative importance of intra- and inter-layer couplings at different doping levels.Comment: 5 pages, 5 figure

Intrinsic response time of graphene photodetectors

Graphene-based photodetectors are promising new devices for high-speed optoelectronic applications. However, despite recent efforts, it is not clear what determines the ultimate speed limit of these devices. Here, we present measurements of the intrinsic response time of metal-graphene-metal photodetectors with monolayer graphene using an optical correlation technique with ultrashort laser pulses. We obtain a response time of 2.1 ps that is mainly given by the short lifetime of the photogenerated carriers. This time translates into a bandwidth of ~262 GHz. Moreover, we investigate the dependence of the response time on gate voltage and illumination laser power

Spatial coherence measurement of a high average power table-top soft X-ray laser

Includes bibliographical references (page 126).An extraordinarily high degree of spatial coherence from a high average power tabletop 46.9 nm laser was observed in two-pinhole interference experiments. Refractive anti-guiding and gain guiding along a capillary discharge-produced plasma column causes a rapid increase of the spatial coherence with amplifier length. Full spatial coherence was approached with a 36 cm long plasma of very high axial uniformity and a length to diameter ratio exceeding 1000: 1

Can Disruption of Basal Ganglia-Thalamocortical Circuit in Wilson Disease Be Associated with Juvenile Myoclonic Epilepsy Phenotype?

In this paper, we describe the multimodal MRI findings in a patient with Wilson disease and a seizure disorder, characterized by an electroclinical picture resembling juvenile myoclonic epilepsy. The brain structural MRI showed a deposition of ferromagnetic materials in the basal ganglia, with marked hypointensities in T2-weighted images of globus pallidus internus bilaterally. A resting-state fMRI study revealed increased functional connectivity in the patient, compared to control subjects, in the following networks: (1) between the primary motor cortex and several cortical regions, including the secondary somatosensory cortex and (2) between the globus pallidus and the thalamo-frontal network. These findings suggest that globus pallidus alterations, due to metal accumulation, can lead to a reduction in the normal globus pallidus inhibitory tone on the thalamo-(motor)-cortical pathway. This, in turn, can result in hyperconnectivity in the motor cortex circuitry, leading to myoclonus and tonic-clonic seizures. We suppose that, in this patient, Wilson disease generated a ‘lesion model’ of myoclonic epilepsy

An AP-1/clathrin coat plays a novel and essential role in forming the Weibel-Palade bodies of endothelial cells

Clathrin provides an external scaffold to form small 50–100-nm transport vesicles. In contrast, formation of much larger dense-cored secretory granules is driven by selective aggregation of internal cargo at the trans-Golgi network; the only known role of clathrin in dense-cored secretory granules formation is to remove missorted proteins by small, coated vesicles during maturation of these spherical organelles. The formation of Weibel-Palade bodies (WPBs) is also cargo driven, but these are cigar-shaped organelles up to 5 μm long. We hypothesized that a cytoplasmic coat might be required to make these very different structures, and we found that new and forming WPBs are extensively, sometimes completely, coated. Overexpression of an AP-180 truncation mutant that prevents clathrin coat formation or reduced AP-1 expression by small interfering RNA both block WPB formation. We propose that, in contrast to other secretory granules, cargo aggregation alone is not sufficient to form immature WPBs and that an external scaffold that contains AP-1 and clathrin is essential