A new security architecture for SIP based P2P computer networks

Many applications are transferred from C/S (Client/Server) mode to P2P (Peer-to-Peer) mode such as VoIP (Voice over IP). This paper presents a new security architecture, i.e. a trustworthy authentication algorithm of peers, for Session Initialize Protocol (SIP) based P2P computer networks. A mechanism for node authentication using a cryptographic primitive called one-way accumulator is proposed to secure the P2P SIP computer networks. It leverages the distributed nature of P2P to allow for distributed resource discovery and rendezvous in a SIP network, thus eliminating (or at least reducing) the need for centralized servers. The distributed node authentication algorithm is established for the P2P SIP computer networks. The corresponding protocol has been implemented in our P2P SIP experiment platform successfully. The performance study has verified the proposed distributed node authentication algorithm for SIP based P2P computer networks

Novel Surface Plasmon Polariton Waveguides with Enhanced Field Confinement for Microwave-Frequency Ultra-Wideband Bandpass Filters

© 2013 IEEE. In this paper, a novel planar waveguide based on spoof surface plasmon polaritons (SSPPs) using fish-bone corrugated slot structure is first proposed in the microwave region. Low-dispersion band can be realized by such structure with tight field confinement of SSPPs, resulting in size miniaturization of the proposed waveguide. The high frequency stopband of the proposed ultra-wideband bandpass filter (BPF) is created by using this proposed waveguide, while the low frequency stopband is properly designed through introducing the microstrip-to-slotline transition. The 2-D E-fields distribution, surface current flow, and energy flow patterns are all calculated and illustrated to demonstrate the electromagnetic (EM) characteristics of the proposed ultra-wideband BPF. The BPF tuning characteristics is explored to provide a guideline for facilitating the design process. To validate the predicted performance, the proposed filter is finally designed, fabricated, and measured. Measured results illustrate high performance of the filter, in which the reflection coefficient is better than -10 dB from 2.1 to 8 GHz with the smallest insertion loss of 0.37 dB at 4.9 GHz, showing good agreement with numerical simulations. The proposed surface plasmon polariton waveguides are believed to be significantly promising for further developing plasmonic functional devices and integrated 2-D circuits with enhanced confinement of SSPPs in microwave and even terahertz bands

Significance of CO2 donor on the production of succinic acid by Actinobacillus succinogenes ATCC 55618

<p>Abstract</p> <p>Background</p> <p>Succinic acid is a building-block chemical which could be used as the precursor of many industrial products. The dissolved CO₂concentration in the fermentation broth could strongly regulate the metabolic flux of carbon and the activity of phosphoenolpyruvate (PEP) carboxykinase, which are the important committed steps for the biosynthesis of succinic acid by <it>Actinobacillus succinogenes</it>. Previous reports showed that succinic acid production could be promoted by regulating the supply of CO₂donor in the fermentation broth. Therefore, the effects of dissolved CO₂concentration and MgCO₃on the fermentation process should be investigated. In this article, we studied the impacts of gaseous CO₂partial pressure, dissolved CO₂concentration, and the addition amount of MgCO₃on succinic acid production by <it>Actinobacillus succinogenes </it>ATCC 55618. We also demonstrated that gaseous CO₂could be removed when MgCO₃was fully supplied.</p> <p>Results</p> <p>An effective CO₂quantitative mathematical model was developed to calculate the dissolved CO₂concentration in the fermentation broth. The highest succinic acid production of 61.92 g/L was obtained at 159.22 mM dissolved CO₂concentration, which was supplied by 40 g/L MgCO₃at the CO₂partial pressure of 101.33 kPa. When MgCO₃was used as the only CO₂donor, a maximal succinic acid production of 56.1 g/L was obtained, which was just decreased by 7.03% compared with that obtained under the supply of gaseous CO₂and MgCO₃.</p> <p>Conclusions</p> <p>Besides the high dissolved CO₂concentration, the excessive addition of MgCO₃was beneficial to promote the succinic acid synthesis. This was the first report investigating the replaceable of gaseous CO2 in the fermentation of succinic acid. The results obtained in this study may be useful for reducing the cost of succinic acid fermentation process.</p

Biomechanical study of the funnel technique applied in thoracic pedicle screw replacement

Background: Funnel technique is a method used for the insertion of screw into thoracic pedicle.Aim: To evaluate the biomechanical characteristics of thoracic pedicle screw placement using the Funnel technique, trying to provide biomechanical basis for clinical application of this technology.Methods: 14 functional spinal units (T6 to T10) were selected from thoracic spine specimens of 14 fresh adult cadavers, and randomly divided into two groups, including Funnel technique group (n=7) and Magerl technique group (n=7). The displacement-stiffness and pull-out strength in all kinds of position were tested and compared.Results: Two fixed groups were significantly higher than that of the intact state (P&lt;0.05) in the spinal central axial direction, compression, anterior flexion, posterior bending, lateral bending, axial torsion, but there were no significant differences between two fixed groups (P&gt;0.05). The mean pull-out strength in Funnel technique group (789.09±27.33) was lower than that in Magerl technique group (P&lt;0.05).Conclusions: The Funnel technique for the insertion point of posterior bone is a safe and accurate technique for pedicle screw placement. It exhibited no effects on the stiffness of spinal column, but decreased the pull-out strength of pedicle screw. Therefore, the funnel technique in the thoracic spine affords an alternative for the standard screw placement.Keywords: Thoracic; Pedicle screws; Biomechanics; Funnel techniqu

Innovative online platforms: Research opportunities

Economic growth in many countries is increasingly driven by successful startups that operate as online platforms. These success stories have motivated us to define and classify various online platforms according to their business models. This study discusses strategic and operational issues arising from five types of online platforms (resource sharing, matching, crowdsourcing, review, and crowdfunding) and presents some research opportunities for operations management scholars to explore

Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE). Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place with the assistance of nanoscale GaN gratings and depends on the grating period P and the grating width W. Importantly, coalescences between two side facets are realized to generate epitaxial gratings with triangular section. Thin epitaxial gratings produce the promising photoluminescence performance. This work provides a feasible way for further GaN-based integrated optics devices by a combination of GaN micromachining and epitaxial growth on a GaN-on-silicon substrate

Smad3 promotes cancer progression by inhibiting E4BP4-mediated NK cell development

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A New Compact and High Gain Circularly-Polarized Slot Antenna Array for Ku-Band Mobile Satellite TV Reception

© 2013 IEEE. A compact and high-gain SIW-fed circularly polarized (CP) slot-antenna array with a stacked feed structure is presented for the application of Ku-band high-data-rate satellite communications. First, a novel probe-fed SIW cavity with four slots etched on the top surface is proposed as a high-gain radiating element for the array. The four slots in the cavity act as a 2\times2 array, and its directivity is 2.15 and 1.43 dB greater than that of the cavity-backed antenna of the same size using ring slot and split ring slot, respectively. Second, a compact 1-4 SIW power divider is designed for exciting a subarray. Third, the 2\times2 subarray is further expanded to an 8\times16 array by adopting an additional layer of 1-32 SIW feeding network to meet the gain requirement of the Ku-band mobile satellite TV reception. Finally, experiments are carried out to verify the designed prototypes. Measured results show that proposed 128-element array has a relative impedance bandwidth of 4.8% (11.84 to 12.42 GHz), AR bandwidth of 130 MHz (12.01 to 12.14 GHz), and a peak gain of 26.8 dBic at 12.06 GHz. Owing to the simple feeding networks and the compact radiating element, the antenna has a compact size of 6.04\lambda 0 \times 11.96\lambda 0 \times 0.1\lambda 0. Experimental results show that the proposed CP antenna array is suitable for applications of Ku-band mobile satellite TV reception

Central metabolism in Mycobacterium smegmatis during the transition from O2-rich to O2-poor conditions as studied by isotopomer-assisted metabolite analysis

Isotopomer-assisted metabolite analysis was used to investigate the central metabolism of Mycobacterium smegmatis and its transition from normal growth to a non-replicating state under a hypoxic environment. Tween 80 significantly promoted aerobic growth by improving O2 transfer, while only small amount was degraded and metabolized via the TCA cycle for biomass synthesis. As the bacillus encountered hypoxic stress, isotopomer analysis suggested: (1) isocitrate lyase activity increased, which further induced glyoxylate pathway and glycine dehydrogenase for replenishing NAD+; (2) the relative amount of acetyl-CoA entering the TCA cycle was doubled, whereas little entered the glycolytic and pentose phosphate pathways

Integrating Flux Balance Analysis into Kinetic Models to Decipher the Dynamic Metabolism of Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 sequentially utilizes lactate and its waste products (pyruvate and acetate) during batch culture. To decipher MR-1 metabolism, we integrated genome-scale flux balance analysis (FBA) into a multiple-substrate Monod model to perform the dynamic flux balance analysis (dFBA). The dFBA employed a static optimization approach (SOA) by dividing the batch time into small intervals (i.e., ∼400 mini-FBAs), then the Monod model provided time-dependent inflow/outflow fluxes to constrain the mini-FBAs to profile the pseudo-steady-state fluxes in each time interval. The mini-FBAs used a dual-objective function (a weighted combination of “maximizing growth rate” and “minimizing overall flux”) to capture trade-offs between optimal growth and minimal enzyme usage. By fitting the experimental data, a bi-level optimization of dFBA revealed that the optimal weight in the dual-objective function was time-dependent: the objective function was constant in the early growth stage, while the functional weight of minimal enzyme usage increased significantly when lactate became scarce. The dFBA profiled biologically meaningful dynamic MR-1 metabolisms: 1. the oxidative TCA cycle fluxes increased initially and then decreased in the late growth stage; 2. fluxes in the pentose phosphate pathway and gluconeogenesis were stable in the exponential growth period; and 3. the glyoxylate shunt was up-regulated when acetate became the main carbon source for MR-1 growth