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Using the self-consistent-charge density-functional tight-binding method (SCC-DFTB) and extended lagrangian DFTB-based molecular dynamics, we performed in silico studies of the behavior of grapheneâ€"nanotube hybrid structures that are part of a branched 3D carbon network in strong electrical fields. It has been established that strong fields with strength ranging from 5 to 10 V nmâˆ'1 cause oscillating deformations of the atomic framework with a frequency in the range from 1.22 to 1.38 THz. It has been revealed that the oscillation frequency is determined primarily by the topology of the atomic framework of grapheneâ€"nanotube hybrid, while the electric field strength has an effect within 1%â€"2%. A further increase in electric field strength reduces the oscillation frequency to 0.7 THz, which accompanies the partial destruction of the atomic framework. The critical value of the electric field strength when the graphene is detached from the nanotube is ∼20 V nmâˆ'1. [ABSTRACT FROM AUTHOR]

A new scheme for generating high power terahertz (THz) radiation by using two obliquely colliding electron beams in plasma is proposed. The particle-in-cell (PIC) simulation finds that a small beam intersection of high electron density is formed within a plasma wavelength when two thin electron beams collide. Meanwhile, the beam intersection can oscillate in a strong plasma wave driven by the two beams to produce THz radiation at double plasma frequency. A theoretical model is established showing that the radiation mechanism is the second-order current generated by the beam intersection oscillation. The angular distribution of the THz radiation is calculated by the theory, which agrees well with the PIC simulation. Compared with the existing high power THz sources, the scheme provided in this article has the advantages of a simple structure and no need for extreme parameter conditions, which is hopeful for applications in kilowatt-level coherent compact THz sources. [ABSTRACT FROM AUTHOR]

Since the successfully synthesis of monolayer graphene, carbon-based materials have attracted wide and extensive attentions from researches. Due to the excellent transport capacity and conductivity, they are promising to be applied in electronic devices, even substituting the silicon-based electronic devices, optoelectronics and spintronics. Nevertheless, due to the non magnetic feature, many efforts have been devoted to endow carbon materials magnetism to apply them in the spintronic devices fabrication. Herein, a strategy of Cr cation solely anchored on two-dimensional carbon nanosheets by Cr–N bonds is developed, which introduces magnetism in carbon nanosheets. By extended x-ray absorption fine structure characterization, Cr cations are demonstrated to be atomically dispersed with Cr–N3 coordination. And after Cr–N3 anchored, carbon nanosheets exhibit ferromagnetic features with paramagnetic background. The magnetization varies with Cr content and reaches the maximum (Cr: 2.0%, 0.86 emu g−1) under 3 T at 50 K. The x-ray magnetic circular dichroism and first-principle calculations indicate that the magnetism is caused by the Cr3+ component of the anchored Cr cations. This study sets a single cation anchoring carbon as a suitable candidate for future spintronics. [ABSTRACT FROM AUTHOR]

Copper oxide nanoparticles (CuO NPs) have anticancer and antimicrobial activities. Moreover, they have a contrast enhancing effect in both MRI and ultrasound. Nonetheless, encapsulation is needed to control their toxic side effects and a mechanism for release on demand is required. A methodology is introduced herein for encapsulating and releasing CuO NPs from micelles by ultrasound induced hyperthermia and monitoring the process by MRI. For this aim, CuO NPs loaded poly(ethylene glycol)-block-poly(D,L-lactic acid) (PEG-b-PLA) micelles were prepared. Then, the profile of copper release with application of ultrasound was examined as a function of time and temperature using a colorimetric method. Finally, T1 weighted MRI images of suspensions and ex vivo poultry liver samples containing the CuO NPs loaded micelles were acquired before and after ultrasound application. The results confirmed that: (i) encapsulated NPs are detectible by MRI T1 mapping, depicting substantial T1 shortening from 1872 ± 62 ms to 683 ± 20 ms. (ii) Ultrasonic hyperthermia stimulated the NPs release with an about threefold increase compared to non-treated samples. (iii) Releasing effect was clearly visible by T1-weighted imaging (mean signal increase ratio of 2.29). These findings can potentially lead to the development of a new noninvasive methodology for CuO NPs based theranostic process. [ABSTRACT FROM AUTHOR]

Magnetic ferrite materials have been extensively studied for a range of technological applications, such as magnetic motors, recording media, and millimetre-wave devices. In this context, the nanosized epsilon phase of Fe2O3 (ϵ-Fe2O3) attracts significant attention due to its high coercive field at room temperature. Here, we report the in-situ aerogel nanoreactor growth of magnetic ϵ-Fe2O3 nanoparticles, exhibiting a coercive field (Hc) of 4000 Oe. We show that the control of nanoreactor plays an important role in the growth of ϵ-Fe2O3 nanoparticles. The findings provide a versatile reaction pathway for the growth of magnetically hard ferrite nanoparticles. [ABSTRACT FROM AUTHOR]

Superparamagnetic iron oxide nanoparticles (SPIONs) and core-shell type nanoparticles, consisting of SPIONs coated with mesoporous silica and/or lipid, were synthesised and tested for their potential theranostic applications in drug delivery, magnetic hyperthermia and as a contrast agent. Transmission Electron Microscopy (TEM) confirmed the size of bare and coated SPIONs was in the range of 5–20 nm and 100–200 nm respectively. The superparamagnetic nature of all the prepared nanomaterials as indicated by Vibrating Sample Magnetometry (VSM) and their heating properties under an AC field confirm their potential for hyperthermia applications. Scanning Column Magnetometry (SCM) data showed that extrusion of bare-SPION (b-SPION) dispersions through a 100 nm polycarbonate membrane significantly improved the dispersion stability of the sample. No sedimentation was apparent after 18 h compared to a pre-extrusion estimate of 43% settled at the bottom of the tube over the same time. Lipid coating also enhanced dispersion stability. Transversal relaxation time (T2) measurements for the nanoparticles, using a bench-top relaxometer, displayed a significantly lower value of 46 ms, with a narrow relaxation time distribution, for lipid silica coated SPIONs (Lip-SiSPIONs) as compared to that of 1316 ms for the b-SPIONs. Entrapment efficiency of the anticancer drug, Doxorubicin (DOX) for Lip-SPIONs was observed to be 35% which increased to 58% for Lip-SiSPIONs. Moreover, initial in-vitro cytotoxicity studies against human breast adenocarcinoma, MCF-7 cells showed that % cell viability increased from 57% for bSPIONs to 82% for Lip-SPIONs and to 87% for Lip-SiSPIONs. This suggests that silica and lipid coatings improve the biocompatibility of bSPIONs significantly and enhance the suitability of these particles as drug carriers. Hence, the magnetic nanomaterials prepared in this work have potential theranostic properties as a drug carrier for hyperthermia cancer therapy and also offer enhancement of contrast agent efficacy and a route to a significant increase in dispersion stability. [ABSTRACT FROM AUTHOR]

Annealing of a magnetic nanostructure is expected to not only change morphological features but also magnetic properties and hence magnetic hyperthermia applications. Using a simple co-precipitation method, annealed and non-annealed MWCNT/CoFe2O4 nanocomposites have been synthesized, as confirmed by phases depicted in XRD. Here, a comparative study of morphological features, magnetic properties and heat dissipation capability of as-synthesized samples has been done. Transmission electron microscopy and scanning electron microscopy images reveal the agglomerated nature of the nanostructure. A visible shift in peak position of FTIR spectroscopy and Raman shift for annealed MWCNT/CoFe2O4 nanocomposites from that of non-annealed MWCNT/CoFe2O4 nanocomposites implies change in the vibrational features. As evident from vibrating sample magnetometer, coercivity and saturation magnetization increases for annealed MWCNT/CoFe2O4 nanocomposites, heat dissipation capability quantified by the specific absorption rate and intrinsic loss parameter is also found to be amplified. [ABSTRACT FROM AUTHOR]

In this work, magnetosomes produced by microorganisms were chosen as a suitable magnetic carrier for covalent immobilization of thermostable trypsin conjugates with an expected applicability for efficient and rapid digestion of proteins at elevated temperatures. First, a biogenic magnetite was isolated from Magnetospirillum gryphiswaldense and its free surface was coated with the natural polysaccharide chitosan containing free amino and hydroxy groups. Prior to covalent immobilization, bovine trypsin was modified by conjugating with α-, β- and γ-cyclodextrin. Modified trypsin was bound to the magnetic carriers via amino groups using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysulfosuccinimide as coupling reagents. The magnetic biomaterial was characterized by magnetometric analysis and electron microscopy. With regard to their biochemical properties, the immobilized trypsin conjugates showed an increased resistance to elevated temperatures, eliminated autolysis, had an unchanged pH optimum and a significant storage stability and reusability. Considering these parameters, the presented enzymatic system exhibits properties that are superior to those of trypsin forms obtained by other frequently used approaches. The proteolytic performance was demonstrated during in-solution digestion of model proteins (horseradish peroxidase, bovine serum albumin and hen egg white lysozyme) followed by mass spectrometry. It is shown that both magnetic immobilization and chemical modification enhance the characteristics of trypsin making it a promising tool for protein digestion. [ABSTRACT FROM AUTHOR]

Based on the combination of a staggered double vane slow wave structure (SWS) and round electron beam, a 200-W W-band traveling-wave tube (TWT) amplifier is studied in this paper. The main advantages of round beam operation over the sheet beam is that the round beam can be formed more easily and the focus requirement can be dramatically reduced. It operates in the fundamental mode at the first spatial harmonic. The geometric parameters are optimized and a transition structure for the slow wave circuit is designed which can well match the signal that enters into and goes out from the tube. Then a TWT model is established and the particle-in-cell (PIC) simulation results show that the tube can provide over 200-W output power in a frequency range of 88 GHz-103 GHz with a maximum power of 289 W at 95 GHz, on the assumption that the input power is 0.1 W and the beam power is 5.155 kW. The corresponding conversion efficiency and gain at 95 GHz are expected to be 5.6% and 34.6 dB, respectively. Such amplifiers can potentially be used in high power microwave-power-modules (MPM) and for other portable applications. [ABSTRACT FROM AUTHOR]

We report a facile approach to synthesizing 3-aminopropyltrimethoxysilane (APTS)-coated magnetic iron oxide (Fe3O4@APTS) nanoparticles (NPs) with tunable surface functional groups for potential biomedical applications. The Fe3O4 NPs with a mean diameter of 6.5 nm were synthesized by a hydrothermal route in the presence of APTS. The formed amine-surfaced Fe3O4@APTS NPs were further chemically modified with acetic anhydride and succinic anhydride to generate neutral (Fe3O4@APTS.Ac) and negatively charged (Fe3O4@APTS.SAH) NPs. These differently functionalized NPs were extensively characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry analysis, zeta potential measurements, and T2 relaxometry. The cytotoxicity of the particles was evaluated by in vitro 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide colorimetric viability assay of cells along with microscopic observation of cell morphology. The hemocompatibility of the particles was assessed by in vitro hemolysis assay. We show that the hydrothermal approach enables an efficient modification of APTS onto the Fe3O4 NP surfaces and the formed NPs with different surface charge polarities are water-dispersible and colloidally stable. The acetylated Fe3O4@APTS.Ac NPs displayed good biocompatibility and hemocompatibility in the concentration range of 0-100 &mgr;g ml-1, while the pristine Fe3O4@APTS and Fe3O4@APTS.SAH particles started to display slight cytotoxicity at a concentration of 10 &mgr;g ml-1. The findings from this study suggest that the Fe3O4@APTS NPs synthesized by the one-pot hydrothermal route can be surface modified for various potential biomedical applications. [ABSTRACT FROM AUTHOR]

Morphological features, reduction and doping degree of graphene could pose varied effects on its electronic configuration, polarization states, and further trigger of magnetic moments. Herein, three different kinds of graphene oxide (GO) with different corrugations: rippled, folded and flower-like GO in combination with urea were used as precursors to synthesize nitrogen doped graphene (NG) via a facile one-step thermal annealing method to simultaneously achieve nitrogen doping and GO reduction. The magnetic and microwave absorption properties of the three kinds of GO and their corresponding NG were evaluated in terms of structure, C/O ratio (GO reduction degree) and nitrogen doping. The overall results revealed that the reduction is more efficient in the few-layered GO but may be hindered by a folded structure which tends to trap the doped nitrogen atoms. In terms of magnetic properties, flower-like GO and NG with a crumpled structure exhibited the highest magnetization. The NG with a flower-like structure and highest C/O showed the best microwave absorption performance with filling content as low as 10 wt.%, reflected in a reflection loss (RL) of  −21.7 dB at 16.8 GHz (d  =  2 mm) and 2.3 GHz of bandwidth. While at the same filling content and absorber thickness, the rippled and folded NGs with lower C/O ratio did not exhibit absorption values of practical application. Thus, higher C/O, proper doping degree and low filler content are required to achieve optimized permittivity and consequently favorable microwave absorbing performance. [ABSTRACT FROM AUTHOR]

Since the first system was established and reported in 2005, magnetic particle imaging (MPI) has emerged as a non-invasive tomographic technique that has proven useful in diagnostic imaging. Magnetic particle spectroscopy (MPS), alternatively called magnetization response spectroscopy, is a novel measurement method that closely relates to MPI. An MPS system can be interpreted as a 0D MPI scanner consisting of excitation field coils and pickup coils. In MPS, a sinusoidal magnetic field with sufficiently large amplitude is applied to superparamagnetic iron oxide nanoparticles (SPIONs), which periodically drives their magnetization into and out of saturation. Their magnetic responses, which contain unique harmonics, are recorded and separated into their spectral components. While prototypes of MPI systems are still in their testing stages, MPS has been actively explored as a portable, highly-sensitive, cheap, in vitro, and easy-to-use bioassay testing kit. In this review, we briefly discuss the superparamagnetism and magnetic relaxation mechanisms associated with MPS measurements. We summarize the recent progress in the various MPS detection modes and, also, MPS-based bioassays. Finally, this review concludes with an insight of the state of art and future trends of MPS-based bioassays. [ABSTRACT FROM AUTHOR]

The development of high capacity wireless networks, to satisfy the increasing demand of mobile high-speed internet, is stimulating the exploitation of the wide frequency bands in the millimeter and THz range. Above 100 GHz, the high atmosphere attenuation is the major obstacle for wireless links of adequate length, due to the low power available from solid state amplifiers. Traveling wave tubes (TWT) are promising devices capable og generating multi-watt power at sub-THz frequency. In this paper, the design and performance of a TWT in the 210–250 GHz band with about 1 W output power will be described, to power a 40 Gigabits per second optical transmitter for 1 km point-to-point link. A novel approach for a simple and low-cost fabrication, based on the use of the double corrugated waveguide is proposed. [ABSTRACT FROM AUTHOR]

Nonclassical crystallization is the process in which crystals grow by deposition of nanoparticles rather than by the layer-wise deposition of atoms/ions/molecules on a crystal surface. A spontaneous generation of charged nanoparticles (CNPs) in the gas phase has been experimentally confirmed during many chemical vapor deposition (CVD) processes. The fact that crystals grown by CNPs have smooth surfaces without any void indicates that CNPs have a liquid-like or superplastic property. Based on this understanding of nonclassical crystallization in CVD processes, the synthesis of nanoparticles, thin films and nanowires can be approached systematically. Since electrical field, drag effect, size and the number of charges per particle affect the behavior of CNPs, electric bias, gas velocity, the size of the nanoparticles and the amount of charge can be new processing parameters. The size distribution of CNPs depends on the process conditions. The nanoparticles can be attracted or repelled by applying an electric bias to a substrate. If the nanoparticles are made to land on the substrate in a suitable number density, they can be used as quantum dots. In addition, nanopowders, nanowires, and nanostructures can be synthesized by CNPs with or without metallic catalysts on substrates. Herein, we will review recent results of the synthesis of nanostructures such as nanoparticles, thin films, and nanowires in the CVD process. We will also discuss the role of charge in these syntheses. [ABSTRACT FROM AUTHOR]

The rapid development of advanced nanotechnology has continuously changed many aspects of society. One important nanostructured material, magnetic nanoparticles (NPs), has applications in many areas including clean energy, biology and engineering because of their special magnetic properties. The synthesis of magnetic nanomaterials with desired sizes and morphology has attracted great attention. Nanomaterials with different properties can be combined to construct multifunctional nanoplatforms through systematic surface engineering. The surface modification of magnetic NPs presents the opportunity for them to be used in many practical applications. Functionalized magnetic NPs have been successfully applied in catalysis, as thermoelectric materials, for drug delivery, as imaging agents in nuclear magnetic resonance and in biosensors. In this review, synthetic methods for magnetic NPs and some of their important properties are described. Then the latest progress of the application of magnetic NPs in energy and biology has been summarized and discussed. Finally, we discuss some issues that still need to be solved and the prospects for magnetic NPs. [ABSTRACT FROM AUTHOR]

Spin-polarized electron momentum densities of Nd-doped nickel ferrites (Ni1−xNdxFe2O4 where , 0.24) at 8 and 300 K temperatures are presented. The measurements have been made using the magnetic Compton scattering set-up available at SPring-8, Japan. The site-specific spin moments which contribute to the formation of the total spin moment are deduced by decomposition of the magnetic Compton profile (MCP) into constituent profiles. An increase in the spin moment at Fe site and a reduction at Ni site with Nd doping, as revealed by MCP data, are explained on the basis of the cationic redistribution at octahedral and tetrahedral sites using x-ray photoelectron spectroscopy (XPS) analysis. The XPS measurements suggest the emergence of Fe2+ ions in Nd-doped samples to maintain the charge neutrality. It is found that the net spin moment at the Nd site is antiparallel to that at Ni and Fe sites. The orbital magnetic moment (deduced from the difference of magnetic Compton and total magnetization data) is also discussed. [ABSTRACT FROM AUTHOR]

The exploration of nanocomposites has gained a strong research following over the last decade. These materials have been heavily exploited in several fields, with applications ranging from biosensors to biomedicine. Among these applications, great advances have been made in the field of microbiology, specifically as antimicrobial agents. This review aims to provide a comprehensive account of various nanocomposites that elucidate promising antimicrobial activity. The composition, physical and chemical properties, as well as the antimicrobial performance of these nanocomposites, are discussed in detail. [ABSTRACT FROM AUTHOR]