Disposable magnetic DNA sensors for the determination at the attomolar level of a specific enterobacteriaceae family gene

Disposable magnetic DNA sensors using an enzyme-amplified strategy for the specific detection of a gene related to the Enterobacteriaceae bacterial family, based on the coupling of streptavidin-peroxidase to biotinylated lacZ gene target sequences, has been developed. A biotinylated 25-mer capture probe was attached to streptavidin-modified magnetic beads and hybridization with the biotinylated target was allowed to proceed. Then, a streptavidin-peroxidase polymer was attached to the biotinylated target, and the resulting modified magnetic beads were captured by a magnetic field on the surface of tetrathiafulvalene (TTF) modified gold screen-printed electrodes (Au/SPEs). The amperometric response obtained at -0.15 V after the addition of hydrogen peroxide was used to detect the hybridization process. In order to improve the sensitivity of the determination and reduce the assay time, different variables of the assay protocol were optimized. A low detection limit (5.7 fmol) with good stability (RSD = 7.1%, n = 10) was obtained. The DNA nonspecific adsorption at the magnetic beads was negligible, the obtained results thus demonstrating the possibility to detect the hybridization event with great specificity and sensitivity. The developed method was used for the analysis of Escherichia coli DNA fragments (326 bases) in polymerase chain reaction (PCR) amplicons extracted from a cell culture. As low as 2.5 aM asymmetric PCR product could be detected with the developed methodology.     

PCR-free DNA detection using a magnetic bead-supported polymeric transducer and microelectromagnetic traps

A fluorescent polymeric hybridization transducer supported on magnetic microbeads was investigated for the rapid, ultrasensitive, and sequence-specific detection of DNA. We show that the polymer derivative can be used to detect target DNA directly on magnetic particles by preparing "target-ready" microbeads grafted with the polymer and suitable DNA probes. A detection limit of approximately 200 target copies in a probed volume of 150 muL (1.4 copies/muL) was obtained for a DNA sequence specific to Candida albicans This detection scheme does not require the release of the hybridized target DNA prior to its detection or the labeling or amplification of the nucleic acids. Furthermore, we show that the fluorescence from these biosensing magnetic beads can be read while magnetically confined in a small volume by a microelectromagnetic trap, which offers the possibility of performing both the preconcentration and detection steps simultaneously on the same support. The combination of the fluorescent polymer biosensor with magnetic particle-assisted DNA preconcentration extends the application of this ultrasensitive biosensor to biological samples with complex matrixes and to integrated lab-on-a-chip platforms, where it could be used for fast multitarget DNA detection in point-of-care diagnostics and field analysis.     

Fluoroimmunoassay for antigen based on fluorescence quenching signal of gold nanoparticles

A unique, sensitive, and highly specific fluoroimmunoassay system for antigen detection using gold and magnetic nanoparticles has been developed. The assay is based on the fluorescence quenching of fluorescein isothiocyanate caused by gold nanoparticles coated with monoclonal antibody. To demonstrate its analytical capabilities, the magnetic nanoparticles were coated with anti-alpha-fetoprotein polyclonal antibodies, which specifically bound with alpha-fetoprotein. Gold nanoparticles coated with anti-alpha-fetoprotein monoclonal antibodies could sandwich the alpha-fetoprotein captured by the magnetic nanoparticle probes. The sandwich-type immunocomplex was formed on the surface of magnetic nanoparticles and could be separated by a magnetic field. The supernatant liquid, which contained the unbound gold nanoparticle probes, was used to quench the fluorescence, and the fluorescence intensity of fluorescein isothiocyanate at 516 nm was proportional to the alpha-fetoprotein concentration. The result showed that the limit of detection of alpha-fetoprotein was 0.17 nM. This new system can be extended to detect target molecules with matched antibodies and has broad potential applications in immunoassay and disease diagnosis.     

Diving behaviour of whale sharks in relation to a predictable food pulse.

We present diving data for four whale sharks in relation to a predictable food pulse (reef fish spawn) and an analysis of the longest continuous fine-resolution diving record for a planktivorous shark. Fine-resolution pressure data from a recovered pop-up archival satellite tag deployed for 206 days on a whale shark were analysed using the fast Fourier Transform method for frequency domain analysis of time-series. The results demonstrated that a free-ranging whale shark displays ultradian, diel and circa-lunar rhythmicity of diving behaviour. Whale sharks dive to over 979.5 m and can tolerate a temperature range of 26.4 degrees C. The whale sharks made primarily diurnal deep dives and remained in relatively shallow waters at night. Whale shark diving patterns are influenced by a seasonally predictable food source, with shallower dives made during fish spawning periods.     

旋转圆柱靶磁控溅射阴极的磁场模拟及结构设计

基于旋转圆柱靶磁控溅射阴极的工作原理,建立其结构模型,并应用ANSYS有限元方法对旋转靶阴极磁场进行了模拟计算,得到了磁场分量Bx在靶材表面上的二维磁场分布规律。通过调节磁铁的宽和高、磁铁间夹角以及设置可移动磁性挡板等方法优化磁场并设计了一种新型磁场结构旋转靶。本研究为旋转靶磁控溅射阴极的磁场结构设计提供了理论依据。     

磁控溅射靶材刻蚀特性的模拟研究

靶材刻蚀特性是研究磁控溅射靶材利用率、薄膜生长速度和薄膜质量的关键因素.本文用有限元 分析软件ANSYS模拟了磁控溅射放电空间的磁场分布,用粒子模拟软件OOPIC Pro(object oriented particle in cell)模拟了放电过程,最后用SRIM(stopping and range of ions in matter)模拟了靶材的溅射特性,得到了靶材的刻蚀形貌和刻蚀速度,并讨论了不同工作气压和不同阴极电压对靶材刻蚀的影响.模拟结果表明:靶材刻蚀形貌与磁场分布有关,磁通密度越强,对应的靶材位置刻蚀越深;靶材的刻蚀速度随阴极电压的增大而增大,而当工作气压增大时,靶材的刻蚀速度先增大后趋向平衡,当工作气压超过一定的值时,刻蚀速度随气压的增大开始减小.模拟结果与实验观测进行了比较,二者符合较好.     

Development of a magnetron sputtering system with an extraordinary strong magnetic field near the target

We have developed a planar sputtering device that uses a melt-processed bulk superconductor to generate the magnetic field. The magnetic field that confines the plasma above the sputtering target is about 1.0 T, which is about 20 times larger than the field normally used for magnetron sputtering. Because of the large magnetic field, discharge at an Ar gas pressure as low as 10⁻³ Pa was possible. In this study, we used the ultra-strong-field sputtering technique for depositing Ga-doped ZnO which is attracting interest as a transparent electrode material. We also studied the effect of employing an auxiliary coil to tailor the magnetic field distribution and discuss how the discharge characteristic had changed.     

Differential effects of magnetic pulses on the orientation of naturally migrating birds

In migratory passerine birds, strong magnetic pulses are thought to be diagnostic of the remagnetization of iron minerals in a putative sensory system contained in the beak. Previous evidence suggests that while such a magnetic pulse affects the orientation of migratory birds in orientation cages, no effect was present when pulse-treated birds were tested in natural migration. Here we show that two migrating passerine birds treated with a strong magnetic pulse, designed to alter the magnetic sense, migrated in a direction that differed significantly from that of controls when tested in natural conditions. The orientation of treated birds was different depending on the alignment of the pulse with respect to the magnetic field. These results can aid in advancing understanding of how the putative iron-mineral-based receptors found in birds'' beaks may be used to detect and signal the intensity and/or direction of the Earth''s magnetic field.     

A Superconducting Magnet UCN Trap for Precise Neutron Lifetime Measurements

Finite-element methods along with Monte Carlo simulations were used to design a magnetic storage device for ultracold neutrons (UCN) to measure their lifetime. A setup was determined which should make it possible to confine UCN with negligible losses and detect the protons emerging from β-decay with high efficiency: stacked superconducting solenoids create the magnetic storage field, an electrostatic extraction field inside the storage volume assures high proton collection efficiency. Alongside with the optimization of the magnetic and electrostatic design, the properties of the trap were investigated through extensive Monte Carlo simulation.     

Pattern Recognition Techniques Applied to the Detection and Classification of Welding Defects by Magnetic Testing

The importance of nondestructive tests cannot be denied nowadays, and their use in the petroleum industry is extremely important to ensure safe operation of the equipment. The magnetic flux leakage (MFL) technique in instrumented pig is frequently used for pipeline inspection to detect weld defects and internal or external corrosion; however, as every nondestructive technique, it may present report errors, caused by several human factors (like lack of theoretical knowledge or experience in the technique applied, tiredness due to long hours of work, and so on) and by the inspection technique itself. Because pattern recognition techniques are already well known and applied in other technological research areas, such as fuzzy logic and artificial neural networks, the possibility to develop an automatic system to detect and classify defects through some nondestructive techniques aroused, mainly for those techniques that actually operate with signal or image interpretation. In the present work, pattern nonlinear classifiers were applied using artificial neural networks, to check the possibility to detect and classify defects in pipelines inspected through magnetic pigs (MFL technique). Several tests were performed on specimens with defects artificially inserted (internal and external corrosion and lack of penetration).     

外加磁场对磁控溅射靶利用率的影响

通过在基片上直接放置一块永久磁铁来研究外加磁场对磁控溅射靶利用率的影响。实验发现 ,外加磁场的引入改变了靶表面附近的磁场分布 ,因而靶的刻蚀环的位置、宽度和深度均发生了明显的变化 ,靶的利用率在S S构型和S N构型中均比无外加磁场时要高。利用空间模拟磁场成功的解释这一实验现象。在S S构型和S N构型中 ,后者靶的刻蚀深度轮廓线比较平坦 ,相对刻蚀深度值更大 ,更能有效地提高靶的利用率     

Structures in superconducting YBa2Cu3O7−δ thin films investigated by magneto-optic technique

Using a reflection magneto-optic technique we have investigated natural inhomogeneities and artificial structures in YBCO thin films exposed to an external magnetic field. The artificial structures were mechanically scratched by scanning a diamond tip with different loading over the film surface. Alternatively planar structures with reduced oxygen content could be patterned by heating the YBCO film with a focused laser beam in nitrogen atmosphere. Depending on the laser annealing parameters different screening properties concerning the applied magnetic field could be achieved.As a magneto-optically active layer we used EuS films evaporated on glass as well as bismuth- and gallium-doped lutetium-iron-garnet films grown onto (111) oriented gadolinium-gal lium-gar net substrates by liquid phase epitaxy. In contrast to measurements with EuS films that show only weak faraday rotation for temperatures higher than 20 K the magneto-optic studies have been expanded to about 60 K by using the garnet films.     

Field and Current Control of the Electrical Conductivity of an Artificial 2D Honeycomb Lattice

The conductivity of a neodymium‐based artificial honeycomb lattice undergoes dramatic changes upon application of magnetic fields and currents. These changes are attributed to a redistribution of magnetic charges that are formed at the vertices of the honeycomb due to the nonvanishing net flux of magnetization from adjacent magnetic elements. It is suggested that the application of a large magnetic field or a current causes a transition from a disordered state, in which magnetic charges are distributed at random, to an ordered state, in which they are regularly arranged on the sites of two interpenetrating triangular Wigner crystals. The field and current tuning of electrical properties are highly desirable functionalities for spintronics applications. Consequently, a new spintronics research platform can be envisaged using artificial magnetic honeycomb lattices.     

CNG储气井井筒腐蚀的漏磁检测探索

为了对CNG储气井安全隐患进行有效检测,根据漏磁检测原理,应用ANSYS对CNG储气井井筒漏磁磁场分布进行模拟.仿真结果表明,在合适的磁化参数下可以有效地检测出腐蚀状况.在此基础上,采用交变磁化方式,以锰锌铁氧体作为磁化材料,用霍尔元件阵列检测漏磁信号,加以计算机组成漏磁检测系统.实验结果表明.该系统能够检测出井筒的缺陷,但是精度还需进一步提高.     

The Attenuation of a Pulsed Field by a Conducting Sheet

Instruments that produce pulsed eddy currents in metals have been used to measure the thickness of one metal on another and to determine the properties of metals. The currents are produced by a pulsed dipole, which is surrounded by a conducting mask with a small aperture near the metal to concentrate the field and thus provide better resolution. A pickup coil near the metal is used to detect the currents. One configuration had the pickup coil on one side of a thin metal sheet with the aperture on the other side. This was analyzed assuming a plane electromagnetic wave with the magnetic field parallel to the surface of the metal. Experimental measurements showed that the attenuation as measured was about one-tenth that predicted by the analysis. An analysis was then made assuming that the magnetic field entered the metal surface perpendicularly to the surface. The results of this analysis were compared with the experimentally obtained results with good agreement. Possibly the main reason for the failure of the earlier plane-wave analysis was the reflection at the metal surfaces.     

Electrical resistivity measurements in permafrost terrain at the Engineer Creek road cut,Fairbanks, Alaska

Electrical resistivity measurements were made at a highway road cut in permafrost terrain using 3 methods (galvanic resistivity, magnetic induction and surface impedance). The purpose of these measurements was to attempt to detect the presence of excess ice (segregated ice and massive ice) in permafrost and to compare various resistivity methods for this purpose. A road cut was used to determine the subsurface soil and ice conditions for interpretation of the measurements. Apparent resistivity values measured by galvanic resistivity, magnetic induction and surface impedance methods increased substantially where the permafrost contained segregated and/or massive ice. These changes in resistivity reflected the location and horizontal extent of segregated and massive ice in the road cut although it was not possible to distinguish segregated ice from massive ice. Seasonal and spatial variations in resistivity suggest that the most favorable time to perform these measurements to detect segregated and massive ice in relatively warm permafrost consisting of fine-grained soils is in the Winter and Spring, when the active layer is frozen. The magnetic induction method is the fastest and simplest method to use under field conditions; however, certain field situations may require measurements with other methods.     

Magnetic in-tube solid phase microextraction

We report a new in-tube solid phase microextraction approach named magnetic in-tube solid phase microextraction, magnetic-IT-SPME. Magnetic-IT-SPME has been developed, taking advantage of magnetic microfluidic principles with the aim to improve extraction efficiency of IT-SPME systems. First, a magnetic hybrid material formed by Fe(3)O(4) nanoparticles supported on SiO(2) was synthesized and immobilized in the surface of a bared fused silica capillary column to obtain a magnetic adsorbent extraction phase. The capillary column was placed inside a magnetic coil that allowed the application of a variable magnetic field. Acetylsalicylic acid, acetaminophen, atenolol, diclofenac, and ibuprofen were tested as target analytes. The application of a controlled magnetic field resulted in quantitative extraction efficiencies of the target analytes between 70 and 100%. These results demonstrated that magnetic forces solve the low extraction efficiency (10-30%) of IT-SPME systems, which is one of their main drawbacks.     

一种双目立体视觉系统的校准方法

基于双目立体视觉系统的图像分析以及人工神经网络的三维空间建模算法,设计了一种针对双目立体视觉相机的校准方法,并可应用于运动目标点的轨迹追踪。将均匀分布目标点的校准平面放置在有效视野内的不同位置,通过双目立体视觉系统来捕获处于不同位置的校准平面图像。在图像处理之后,使用校准点中心的二维坐标作为人工神经网络训练的输入样本集,通过建立人工神经网络模型结构,实现目标点二维平面坐标到三维空间坐标的映射关系。采用这种具有通用性的方法,可以有效修正系统中存在的失真因子,获得目标三维位置信息,而无需进行复杂的相机校准操作。实验表明,提出的方案具有良好的可行性和鲁棒性。     

外加磁场对磁控溅射过程及薄膜物性的影响

通过在放电空间中引入垂直基片方向有梯度的磁场,使得利用普通的平面磁控溅射技术可以方便地制备磁性薄膜。与此同时,磁性薄膜的许我物理性能发生了变化。这种变化还出现于非磁性靶的情况中。本工作对有、无磁场时溅射的过程与结果作了比较,包括自偏压值,薄膜结晶状况,薄膜磁性能的变化等等。通过比较认为,带电粒子在放电空间中的特殊磁场位形中的运动是变化的根本原因。     

Design and Evaluation of Magnetic Fields for Nanoparticle Drug Targeting in Cancer

The retention of superparamagnetic nanoparticles under the influence of a high-gradient magnetic field was investigated. A simulation algorithm for prediction of the particle's trajectories and, therefore, the total amount of adhered particles in an artificial vessel was developed. Comparisons between in vitro experiments and simulations showed that the required experimental magnetic moments were greater than the theoretically estimated magnetic moments. This paper presents a method for investigating magnetic fields and for determining the magnetic moment of particles by simulation of their trajectories. The detailed function of magnetic drug targeting is of great importance in animal studies and in human therapies