Structural analysis of the GAP-related domain from neurofibromin and its implications

Neurofibromin is the product of the NF1 gene, whose alteration is responsible for the pathogenesis of neurofibromatosis type 1 (NF1), one of the most frequent genetic disorders in man. It acts as a GTPase activating protein (GAP) on Ras; based on homology to p120GAP, a segment spanning 250-400 aa and termed GAP-related domain (NF1GRD; 25-40 kDa) has been shown to be responsible for GAP activity and represents the only functionally defined segment of neurofibromin. Missense mutations found in NF1 patients map to NF1GRD, underscoring its importance for pathogenesis. X-ray crystallographic analysis of a proteolytically treated catalytic fragment of NF1GRD comprising residues 1198-1530 (NF1-333) of human neurofibromin reveals NF1GRD as a helical protein that resembles the corresponding fragment derived from p120GAP (GAP-334). A central domain (NF1c) containing all residues conserved among RasGAPs is coupled to an extra domain (NF1ex), which despite very limited sequence homology is surprisingly similar to the corresponding part of GAP-334. Numerous point mutations found in NF1 patients or derived from genetic screening protocols can be analysed on the basis of the three-dimensional structural model, which also allows identification of the site where structural changes in a differentially spliced isoform are to be expected. Based on the structure of the complex between Ras and GAP-334 described earlier, a model of the NF1GRD-Ras complex is proposed which is used to discuss the strikingly different properties of the Ras-p120GAP and Ras-neurofibromin interactions.     

Local oscillator chain for 1.55 to 1.75THz with 100-/spl mu/W peak power

We report on the design and performance of a fix-tuned /spl times/2/spl times/3/spl times/3 frequency multiplier chain that covers 1.55-1.75THz. The chain is nominally pumped with 100mW at W-band. At 120K the measured output power is larger than 4/spl mu/W across the band with a peak power of 100/spl mu/W at 1.665THz. A similar chain operated at room temperature produced a peak power of 21/spl mu/W. These power levels now make it possible to deploy multipixel heterodyne imaging arrays in this frequency range.     

Improved mass transfer and biodegradation rates of naphthalene particles using a novel bead mill bioreactor

One of the main challenges in the treatment of polycyclic aromatic hydrocarbons (PAHs) in controlled bioreactors is the hydrophobicity and low solubility of these compounds in the aqueous phase, resulting in appreciable mass transfer limitations within the bioreactor. To address this challenge, we have developed a modified roller bioreactor (Bead Mill Bioreactor) in which inert particles are used to improve mass transfer from the solid phase to the aqueous phase. Experimental results with naphthalene as a model PAH and Pseudomonas putida as a candidate bacterium indicate that both the mass transfer rate from the solid phase to liquid phase and the biodegradation rate in the Bead Mill Bioreactor (BMB) were significantly higher than those in a conventional roller bioreactor (20‐fold and 5.5‐fold, respectively). The enhancement of mass transfer was dependent on the type, size and volumetric loading of the inert particles, as well as concentration of particulate naphthalene. The highest mass transfer coefficient (k_La = 2.1 h^?1) was achieved with 3 mm glass beads at a volumetric loading of 50% (particle volume/working volume) with 10 000 mg dm^?3 particulate naphthalene. The maximum biodegradation rate of naphthalene attained in the bead mill bioreactor (59.2 mg dm^?3 h^?1 based on the working volume and 118.4 mg dm^?3 h^?1 based on the liquid volume) surpasses most other rates published in the literature and is equivalent to values reported for more complex bioreaction systems. The bead mill bioreactor developed in the present work not only enjoys a simple design but shows excellent performance for treatment of PAHs suspended in an aqueous phase. This fundamental information will be of significant value for future studies involving soil‐bound PAHs. Copyright © 2005 Society of Chemical Industry     

Electroosmotic micropump for lab‐on‐a‐chip biomedical applications

Lab‐on‐a‐chip (LOC) integrated microfluidics has been a powerful tool for new developments in analytical chemistry. These microfluidic systems enable the miniaturization, integration and automation of complex biochemical assays through the reduction of reagent use and enabling portability. Electroosmotic micropumps could be employed as powerful tools to generate required flow in point of care (POC) devices. In the present study, parallel electroosmotic micropumps are investigated to improve the efficiency of simple micropumps. According to the results, parallel micropumps generate higher flow rate in comparison with conventional electroosmotic pump. In the last decade, a large variety of non‐Newtonian fluids have been utilized in biomedical application but requirements for a POC device such as high efficient driving flow, miniaturization and simple handling of POC devices remain unmet. As a consequence, in this study, power law model as non‐Newtonian fluids that flow through the parallel micropumps are investigated in order to enhance fluid pumping and decreasing voltage requirement.. It is found that as the power law index increases the mass flow rate decreases. Also, the flow rate is almost constant for the higher power law index. Obtained results, demonstrated that parallel micropump could enhance pumping of non‐Newtonian fluid (blood) up to 30%. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation,morphology and conductivity of polyacrylonitrile/multi-wall carbon nanotubes composite nanofibers

Composite nanofibers of polyacrylonitrile/multi-wall carbon nanotubes (PAN/MWCNTs) were prepared via electrospinning. Samples contained 0, 0.5, 1, 2, 3, and 3.5 wt% of MWCNTs. The viscosity and electrical conductivity of electrospinning solutions were measured. Results revealed that, with the addition of multi-wall carbon nanotubes, viscosity was increased and electrical conductivity was improved. Rheological behavior was studied using two different viscometers. Moreover, morphology and diameters of the composite nanofibers were studied by scanning electron microscopy (SEM) and nanofiber diameter distributions were presented. SEM micrographs showed that by adding MWCNTs, the average diameter of nanofibers was increased. Furthermore, the effect of MWCNTs on glass transition temperature, T _g, was investigated using differential scanning calorimetry (DSC) technique. The results showed that T _g was increased with the addition of MWCNTs. In addition, Fourier transform infrared spectroscopy (FTIR) results showed that MWCNTs can affect the orientation ability of polymer chains. The effects of adding salt, increasing voltage and changing the tip-to-collector distance on the morphology and diameters of composite nanofibers were examined. The electrical conductivity results of electrospun mats were measured by a two-probe method. Electrical conductivity was increased by addition of MWCNTs and its behavior followed the percolation theory. Finally, it was observed that mats with smaller diameters have higher electrical conductivity.     

3D experimental and numerical analysis of wind flow around domed-roof buildings with open and closed apertures

This paper presents experimental and numerical study of airflow distribution around a reduced-scale model of a common type of domed-roof building. Measurements are performed in an open loop wind tunnel. A new modified Counihan scheme is developed for constructing a part-depth atmospheric boundary layer (ABL). Measured quantities include: wind velocity profile, turbulence intensity and airflow pattern around the building. To conduct the experiments, a 1:54 scale model of a real domed-roof building with six windows and an aperture on the roof is fabricated and placed in the test section of the wind tunnel. In addition, using a numerical modeling, turbulent airflow around such scale model in the wind tunnel is simulated and airflow field inside and outside the model as well as ventilating discharge coefficient are computed. It is illustrated that, airflow around this type of building contains complex adjacent recirculation flows. The building with open apertures has acceptable discharge coefficient for ventilation, which can be a factor to ensure comfort condition for residents as well as complying with energy-saving considerations.     

Optimal Resource Allocation in Heterogeneous MIMO Cognitive Radio Networks

The optimal resource allocation in MIMO cognitive radio networks with heterogeneous secondary users, centralized and distributed users, is investigated in this work. The core aim of this work is to study the joint problems of transmission time and power allocation in a MIMO cognitive radio scenario. The optimization objective is to maximize the total capacity of the secondary users (SUs) with the constraint of fairness. At first, the joint problems of transmission time and power allocation for centralized SUs in uplink is optimized. Afterwards, for the heterogeneous case with both the centralized and distributed secondary users, the resource allocation problem is formulated and an iterative power water-filling scheme is proposed to achieve the optimal resource allocation for both kinds of SUs. A dynamic optimal joint transmission time and power allocation scheme for heterogeneous cognitive radio networks is proposed. The simulation results illustrate the performance of the proposed scheme and its superiority over other power control schemes.     

IGBDD: Intelligent Grid Based Data Dissemination Protocol for Mobile Sink in Wireless Sensor Networks

Lifetime and energy efficiency are important factors in the design of wireless sensor network. A critical issue during data collection is the formation of energy holes near the sink. Sensors which are located near the sink have to participate in relaying data on behalf of other sensors and thus their energy will be depleted very quickly. Mobile sink movement yields the significant performance gained by decreasing the amount of energy consumption. In this paper, we propose an Intelligent Grid Based Data Disseminating protocol for mobile sink in wireless sensor networks. We have utilized a virtual grid as the protocol’s substructure. In our proposed method, cell heads (CHs) will be selected based on the locations of virtual cross points (CPs) and CPs selection is needless to transfer any required data between neighbor nodes. We have optimized CPs selection using linear programming technique in order to increase network lifetime. By selecting the CHs based on our proposed algorithm, data will be disseminated toward the sink. Our data dissemination protocol is simple and has low overhead to construct and maintain. Also, we have presented a new method for sink location update which leads to the least cost in data transfer. Simulation results illustrate that by utilizing hierarchical functionality and selecting appropriate CPs and consequently selecting CHs, energy consumption will be decreased in comparison with other presented methods which directly lead to network lifetime increment. Also by determining an optimal cell size, packet delivery rate will be improved noticeably.     

Dynamic analysis of carbon nanotubes under electrostatic actuation using modified couple stress theory

Modified couple stress theory is a size-dependent theorem capturing the micro/nanoscale effects influencing the mechanical behaviors of the micro- and nanostructures. In this paper, it is applied to investigate the nonlinear vibration of carbon nanotubes under step DC voltage. The vibration, natural frequencies and dynamic pull-in characteristics of the carbon nanotubes are studied in detail. Moreover, the effects of various boundary conditions and geometries are scrutinized on the dynamic characteristics. The results reveal that application of this theory leads to the higher values of the natural frequencies and dynamic pull-in voltages.     

Synthesis and characterization of paclitaxel-imprinted nanoparticles for recognition and controlled release of an anticancer drug

Imprinted nanoparticles as drug delivery carriers have been considered because owing to their cross-linked network, they act as the drug reservoir for controlled release. In this study, selective MIPs nanoparticles of paclitaxel (PTX) were successfully developed for application in the biological molecular recognition and in the design of new anticancer drug delivery systems. The MIPs nanoparticles prepared by miniemulsion polymerization technique using methacrylic acid (MAA) and methyl methacrylate as non-covalent functional monomer, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate (TRIM) as cross-linker agent, azobisisobutyronitrile as initiator, and hexadecane as hydrophobic agent. In order to prepare of MIP nanoparticles, the synthesis conditions and effective parameters, such as: cross-linker agent, different molar ratios of template–functional monomer–cross-linker agent, were investigated. In addition, the effect of different molar ratios of template and monomers on polymers binding and morphology were characterized. Structure and thermal properties of MIPs were confirmed by FT-IR spectroscopy and thermogravimetric analysis. Imprinted nanoparticles showed significant drug loading and encapsulation efficiency, 17.8 and 100 %, respectively. The particle size of MIP nanoparticles varies between 187 and 726 nm, according the SEM images and laser light scattering data. The imprinted nanoparticles showed satisfactory affinity (84 %) to PTX with a binding of 12 times higher than non-imprinted nanoparticles in biological samples when MAA and TRIM were used as functional and cross-linker monomer, respectively. Results from release experiments of MIPs showed a very slow and controlled release of PTX which would be helpful for sustained drug delivery.