Magnetic properties of annealed core-shell CoPt nanoparticles

A precise control and understanding of the magnetization dynamics of nanostructures is an important topic in applied nanosciences. Herein, we perform such control by annealing crystalline (Co/core)-(Pt/shell) nanoparticles. Using electron tomography, temperature dependent electron microscopy and time-resolved magneto-optics, we establish a clear correlation between the magnetization dynamics and the crystalline structure of the nanoparticles. For a mild laser annealing (370 K) the Co-Pt nanoparticles keep their core-shell structure and remain superparamagnetic with a blocking temperature T(B) = 66 K. Their time-resolved reflectivity shows that they are locally organized into a supra-crystalline ordered layer in the region of the laser spot. In contrast, a thermal annealing at higher temperatures (up to 700 K) modifies the structure of the individual nanoparticles into a CoPt crystalline ferromagnetic phase, with T(B,anneal) = 347 K. Correspondingly, the magneto-crystalline anisotropy of the annealed CoPt nanoparticles increases and their magnetization dynamics displays a motion of precession, characteristic of ferromagnetic nanostructures and which is absent in the superparamagnetic Co-Pt core-shells.     

Guided-mode-resonance-coupled plasmonic-active SiO(2) nanotubes for surface enhanced Raman spectroscopy

We demonstrate a surface enhanced Raman scattering (SERS) substrate by integrating plasmonic-active SiO(2) nanotubes into Si(3)N(4) gratings. First, the dielectric grating that is working under guided mode resonance (GMR) provides enhanced electric field for localized surface plasmon polaritons on the surface of metallic nanoparticles. Second, we use SiO(2) nanotubes with densely assembled silver nanoparticles to provide a large amount of "hot spots" without significantly damping the GMR mode of the grating. Experimental measurement on Rhodamine-6G shows a constant enhancement factor of 8?～?10 in addition to the existing SERS effect across the entire surface of the SiO(2) nanotubes.     

Optimizations of friction stir welding of aluminum alloy by using genetically optimized neural network

Genetically optimized neural network systems (GONNS) was developed to simulate the intelligent decision-making capability of human beings. After they are trained with experimental data or observations, GONNS use one or more artificial neural networks (ANN) to represent complex systems. The optimization is performed by one or more genetic algorithms (GA). In this study, the GONNS was used to estimate the optimal operating condition of the friction stir welding (FSW) process. Five separate ANNs represented the relationship between two identical input parameters and each one of the considered characteristics of the welding zone. GA searched for the optimized parameters to make one of the parameters maximum or minimum, while the other four are kept within the desired range. The GONNS was found as an excellent optimization tool for FSW.     

Coefficient memory addressing scheme for high performance FFTprocessors

A novel scheme for coefficient address generation in a fast Fourier transform (FFT) processor is presented. The proposed addressing scheme involves manipulation of the address lines taking into consideration coefficient addresses required at various FFT stages. It is demonstrated that the scheme can be implemented more efficiently with much reduced hardware than approaches published to date, leading to faster, more power and area efficient realisation of FFT processors     

Evaluation of the expanded relative uncertainty of NIS developed dead weight machine

Force and Material Metrology Department (FMMD) is a department within the National Institute for Standards (NIS), founded as early as 1963. The most important event achieved within the last few years at FMMD was constructing, evaluating & commissioning of Dead Weight Machines (DWMs), the Primary Standards for force measurements with ranges of 0.05–5kN, 0.5–50kN, 10–500kN, 500–1000kN and 100–5000kN. All are computerized and delivered by GTM Company except the 5kN machine which is a manually controlled machine, established through research works carried out by FMMD [1]. The FMMD was transferred to a new building which lead to dismantling the 5kN machine and re-assembling it in its new site. In addition, the machine was developed as a part of modernizing NIS force laboratory [2].This development entailed checking the design of machine main frame using finite element method, determining the gravitational acceleration in the new building, determining the air density surrounding the machine, adjusting the machine weights to enhance the accuracy associated with the measurement results, beside designing a full computerized control circuits to control the selection and application of the loads of the machine and finally estimating the relative expanded uncertainty of the machine.     

The influence of harvest time on essential oil composition,phenolic constituents and antioxidant properties of Turkish oregano (Origanum onites L.)

BACKGROUND: The aim of this research was to determine essential oil composition, phenolic constituents and antioxidant properties of Turkish oregano (Origanum onites L.) leaves harvested during the months of June to September. RESULT: The maximum essential oil yield in the leaves appeared in the middle of July. The main components of oregano oil were carvacrol, thymol, γ‐terpinene, p‐cymene, α‐terpinene and α‐pinene. Carvacrol was highest in the July harvest. The maximum extract yield was found in September. Oil distilled from early‐season (June) harvested leaves had the highest antioxidant ability, expressed as low concentration providing 50% inhibition of free radical scavenging activity and high levels of reducing/antioxidant capacity. Twelve phenolic compounds of oregano extract were identified and the main components were found to be rosmarinic acid and acecetin. The maximum rosmarinic acid and acecetin were found in harvests of July and June, respectively. Total phenolic contents, free radical scavenging activities and reducing/antioxidant capacities were found to be highest in the July harvest. DISCUSSION: All yields, chemical compositions, free radical scavenging activities and reducing/antioxidant capacities of extracts and essential oils of Turkish oregano changed importantly depending on vegetative periods of growing season. Copyright © 2009 Society of Chemical Industry     

Integration of Homogeneous and Heterogeneous Catalytic Processes for a Multi-step Conversion of Biomass: From Sucrose to Levulinic Acid, γ-Valerolactone, 1,4-Pentanediol, 2-Methyl-tetrahydrofuran, and Alkanes

The multi-step conversion of sucrose to various C₅-oxygenates and alkanes was achieved by integrating various homogeneous and heterogeneous catalytic systems. We have confirmed that the dehydration of sucrose to levulinic and formic acids is currently limited to about 30–40% in the presence of H₂SO₄, HCl, or Nafion NR50 in water. Performing the dehydration in the presence of a P(m-C₆H₄SO₃Na)₃ modified ruthenium catalyst under hydrogen resulted in the in situ conversion of levulinic acid to γ-valerolactone (GVL). Levulinic acid can be hydrogenated to GVL quantitatively by using P(m-C₆H₄SO₃Na)₃ modified ruthenium catalyst in water or Ru(acac)₃/PBu₃/NH₄PF₆ catalyst in neat levulinic acid. Formic acid can be used for the transfer hydrogenation of levulinic acid in water in the presence of [(η⁶-C₆Me₆)Ru(bpy)(H₂O)][SO₄] resulting in GVL and 1,4-pentanediol. The hydrogenation of levulinic acid or GVL can be performed to yield 1,4-pentanediol and/or 2-methyl-tetrahydrofuran (2-Me-THF). The hydrogenolysis of 2-Me-THF in the presence of Pt(acac)₂ in CF₃SO₃H resulted in a mixture of alkanes. We have thus demonstrated that the conversion of carbohydrates to various C₅-oxygenates and even to alkanes can be achieved by selecting the proper catalysts and conditions, which could provide a renewable platform for the chemical industry.     

用于家用电器、控制器和交流电源的协同式电路保护

用高分子聚合物正温度系数器件(PPTC)实现的过流、过热协同保护技术可以保护家用电器中的电动机,控制器和电子元件.PPTC器件的电阻小,尺寸与熔断器相同,在出现故障时,会限制危险的大电流流过.不过,在排除了故障并且切断电源之后,PPTC器件会恢复原来的低电阻状态,它所保护的设备仍能正常工作.