Steep Field Gradients Research Articles

τSPECT: a spin-flip loaded magnetic ultracold neutron trap for a determination of the neutron lifetime

The confinement of ultracold neutrons (UCNs) in three-dimensional magnetic field gradient or magneto-gravitational traps allows for a measurement of the free neutron lifetime τ n with superior control over loss channels related to UCNs interacting with material surfaces. The most precise measurement τ n has been achieved using a magneto-gravitational trap, in which UCN are prevented from escaping at the top of their trap by gravity. More compact horizontal confinement geometries with variable energy acceptance ranges can be obtained by using steep magnetic field gradients in all spatial directions, generated by combinations of either permanent or (variable) superconducting magnets. In this paper, we present the first successful implementation of a pulsed spin-flip based loading scheme to fill a three-dimensional magnetic trap with externally produced UCN. The measurements with the τSPECT experiment were performed at the pulsed UCN source of the research reactor TRIGA Mainz. The extracted neutron storage time constant of τ = 859(16) s is compatible with the most precise determinations of τ n . We report on detailed, but statistically limited, investigations of major systematic effects influencing the neutron storage time. The statistical limitations are mitigated by the relocation of the experiment to a stronger UCN source.

Mixed variational formulation and finite-element implementation of second-order poro-elasticity

We present a variational formulation of second-order poro-elasticity that can be readily implemented into finite-element codes by using standard Lagrangian interpolation functions. Point of departure is a two-field minimization principle in terms of the displacement and the fluid flux as independent variables. That principle is taken as a basis for the derivation of continuous and incremental saddle-point formulations in terms of an extended set of independent variables. By static condensation this formulation is then reduced to a minimization principle in terms of the displacement and fluid flux as well as associated higher-order fields. Once implemented into a finite-element code, the resulting formulation can be applied to the numerical simulation of porous media in consideration of second-order effects. Here, we analyze the model response by means of several example problems including two standard tests in poro-elasticity, namely the consolidation problems of Terzaghi and Mandel, and compare the results with those of a corresponding first-order model. As becomes clear, the second-order formulation can unleash its full potential when applied to the study of porous media having spatial dimensions comparable to the size of their microstructure. In particular, it is capable to regularize steep field gradients at external as well as internal surfaces and to describe material dilatation effects known from experiments.

Investigation of Operational Parameters for Nanoelectrokinetic Purification and Preconcentration.

This work reports on experimental investigations into the operational parameters of nanoelectrokinetic purification and preconcentration, especially utilizing on ion concentration polarization (ICP). ICP as a nanoscale electrokinetic phenomenon has demonstrated promising advances in various fields utilizing an ion depletion zone (IDZ) with a steep electric field gradient inside the ICP layer. However, the inevitable electrokinetic instability occurring within the IDZ has posed a challenge in operating the ICP system stably. To address the need for a stable and efficient ICP operation in various devices and applications, we propose an operational strategy along with conducted research to determine optimal operating ranges. In order to investigate the operational parameters, a unit voltage (VTH) is introduced as the threshold for initiating ICP. We examined the applicability of VTH across various operating ranges to ensure its effectiveness and versatility. In ICP purification, we categorize three modes (steady, burst, and unsteady) based on IDZ expansion and stability under varying VTH and flow rate conditions, presenting optimal operational conditions that minimize the voltage margin. In ICP preconcentration, a systematic investigation is conducted to observe the influence of background electrolyte concentration and voltage conditions on preconcentration efficiency, offering insights into the correlation between preconcentration factor, electrical conditions, and preconcentration time. Therefore, this research would contribute to the practical understanding of nanoelectrokinetics, providing insight into experimental designs. These findings are expected to offer valuable guidance to researchers aiming to utilize ICP's potential across a spectrum of applications, from purification to preconcentration, in the realm of micro/nanofluidic systems.

Acupuncture and Static Multipolar Magnets: An Emerging Attraction?

Magnetism has been known for >4,000 years. Recently static multipolar magnets have demonstrated analgesic clinical usefulness. Local application of magnets may be beneficial in reducing musculoskeletal pain, particularly when other modalities have failed. A recent series of clinical cases demonstrates how multipolar magnets may be incorporated as an effective adjunctive treatment in an acupuncture clinic. PubMed database was searched using the key words: magnets, medical magnets, magnets and pain management, therapeutic magnets, multipolar magnets, and history of magnet therapy. In addition, clinical cases were submitted by 4 different medical acupuncturists as examples of how the use of multipolar magnets is incorporated into an acupuncture clinic. Over the past 20 years, 143 articles fulfilled the search criteria and unfortunately demonstrated considerable variability in research methodology. Magnetic tapes, needles, and beads of various magnetic strengths constituted the stimulating apparatus with durations ranging from minutes to years. This article highlights 10 cases, 9 of which reflected situations in which the use of 1 or more multipolar magnets provided an enhanced analgesic effect, often when traditional acupuncture had either failed to produce a satisfactory response or when the application of acupuncture needles needed to be limited. Despite the variability of the literature review, it appears that magnetism is related to pain reduction, and when properly employed, it can be an effective and safe modality as demonstrated by a recent series of cases submitted from the practices of 4 different medical acupuncturists. A clinical trial incorporating the latest technology of multipolar magnets with steep field gradients should be initiated for the more formal investigation of magnet-induced analgesia.

Nanogap Electrode-Enabled Versatile Electrokinetic Manipulation of Nanometric Species in Fluids.

Noninvasive manipulation of nanoscopic species in liquids has attracted considerable attention due to its potential applications in diverse fields. Many sophisticated methodologies have been developed to control and study nanoscopic entities, but the low-power, cost-effective, and versatile manipulation of nanometer-sized objects in liquids remains challenging. Here, we present a dielectrophoretic (DEP) manipulation technique based on nanogap electrodes, with which the on-demand capturing, enriching, and sorting of nano-objects in microfluidic systems can be achieved. The dielectrophoretic control unit consists of a pair of swelling-induced nanogap electrodes crossing a microchannel, generating a steep electric field gradient and thus strong DEP force for the effective manipulation of nano-objects microfluidics. The trapping, enriching, and sorting of nanoparticles and DNAs were performed with this device to demonstrate its potential applications in micro/nanofluidics, which opens an alternative avenue for the non-invasive manipulation and characterization of nanoparticles such as DNA, proteins, and viruses.

Domain wall dynamics in (Co/Ni)n nanowire with anisotropy energy gradient for neuromorphic computing applications

Artificial Intelligence (AI) has been gaining traction recently. However, they are executed on devices with the von Neumann architecture, requiring high power input. Consequently, brain-inspired neuromorphic computing (NC) has been gaining attention because it is expected to be more power efficient and more suitable for AI. Designing of NC circuits involves development of artificial neurons and synapses. More studies have hitherto been focused on artificial synapses instead of neurons because the latter should demonstrate leaky integrate-and-fire (LIF) properties, which is a challenge to replicate artificially. In this work, we propose a domain wall (DW) based device made from perpendicularly magnetized (Co/Ni)n nanowire (NW) with graded magnetic anisotropy and saturation magnetization. The DW is current-driven via spin-transfer-torque. Micromagnetic simulations demonstrated that the DWs in NWs with anisotropy field gradients can automatically return towards the initial position when electrical current is absent, indicative of the leakage process. The underlying physics of DW motion in such structure was studied in detail. To replicate the crystallinity of (Co/Ni)n structures, granular NWs were also defined. Depending on the grain structure of the NW, it was found that LIF properties were achieved under the conditions of steep anisotropy field gradients. Therefore, the proposed design has potential applications in neuron devices.

Observation of the 87Rb 5S1/2 to 4D3/2 electric quadrupole transition at 516.6 nm mediated via an optical nanofibre

Light guided by an optical nanofibre has a very steep evanescent field gradient extending from the fibre surface. This gradient can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S1/2 → 4D3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87Rb atoms using only a few μW of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the range of applications for optical nanofibres in atomic physics to include more fundamental tests such as high-precision measurements of parity non-conservation.

Numerical Computations of Biomagnetic Fluid Flow in a Lid Driven Cavity

The study on the effects of biological fluids in the presence of magnetic field is known as biomagnetic fluid dynamics (BFD) and the most common biological fluid that exhibit such magnetic properties is blood. An extensive research work has been done in this area due to its applications in medical and bioengineering. Basically, it is essential for a study to be justified according to certain benchmark before progressing. Hence, biomagnetic fluid flow in a lid driven cavity is numerically investigated by utilizing two numerical schemes: finite difference and finite element methods. The formulation adopted is consistent with the principles of ferrohydrodynamics. The mathematical model describes Newtonian blood flow under the influence of a spatially varying magnetic field. The model considers the biofluid as non-conducting. The flow is assumed to be two-dimensional, steady, laminar and isothermal. The implementation of finite element method shows stability issue due to extremely steep magnetic field gradient while finite difference method shows no issue. Due to this, a solution is proposed to alleviate the problem and the result for various magnetic field intensity presented.

Modulating relaxation responses of magnetic nanotracers for submillimeter imaging

Frequency-dependent magnetization characteristics potentially promote magnetic nanoparticles as prominent nanotracers for tomographic imaging. Owing to fast Neel dynamics relative to Brownian rotation of colloidal magnetic nanoparticles, we can demonstrate a two-dimensional image reconstruction from the Néel and Brownian relaxation responses modulated by external oscillatory field bursts with two distinctive frequencies. To realize a micrometer-scale resolution, a field-free-point (FFP) is manipulated to move in a dense Lissajous trajectory by low-frequency perpendicular sinusoidal fields across a steep field gradient between two permanent magnets. Instead of directly recording the resulting harmonic responses, we use an orthogonal high-frequency field to probe the time-varying FFP movement coupled with the moment relaxation. The proposed method achieves high spatial resolution, irrespective of the nonlinearity of the magnetization response, making it practical for bioanalytical imaging of cells and small animal models.

Modelling the partial melting of metasediments in a low-pressure regional contact aureole: the effect of water and whole-rock composition

AbstractLow-pressure regional aureoles with steep metamorphic field gradients are critical to understanding progressive metamorphism in high-temperature metasedimentary rocks. Delicately layered pelitic and psammitic metasedimentary rocks at Mt Stafford, central Australia, record a greenschist- to granulite-facies Palaeoproterozoic regional aureole, associated with S-type granite plutons, reflecting metamorphism in the range 500–800 °C and at ∼3 kbar. The rocks experienced minimal deformation during metamorphism and partial melting. Partial melting textures evolve progressively along the steep metamorphic field gradient from the incipient stages of melting marked by cuspate grains with low dihedral angles, to melt proportions sufficient to form diatexite with schollen. Phase equilibria modelling in the NCKFMASHTO system for pelitic, semi-pelitic and high- and low-ferromagnesian psammitic samples quantitatively illustrates the dependence of partial melting on rock composition and water volume. Pelitic compositions are more fertile than psammitic compositions when the water content in the rocks is low, especially during the early stages of melting. The whole-rock ferromagnesian component additionally influences melt fertility, with ferromagnesian-rich psammite being more fertile than psammite with a lower ferromagnesian component. Subtle variations in free water content can result in obvious changes in melt volume but limited variation in melt composition. Distinct melting histories of pelitic and psammitic rocks inferred from field relationships may be partially attributed to potential differences in water volume retained to super-solidus conditions. Melt composition is more dependent on the rock composition than the variation in water content.

Carrier trajectory tracking equations for Simple-band Monte Carlo simulation of avalanche multiplication processes

Avalanche photodiodes (APDs) with steep electric field gradients generally have low excess noise that arises from carrier multiplication within the internal gain of the devices, and the Monte Carlo (MC) method is among popular device simulation tools for such devices. However, there are few articles relating to carrier trajectory modeling in MC models for such devices. In this work, a set of electric-field-gradient-dependent carrier trajectory tracking equations are developed and used to update the positions of carriers along the path during Simple-band Monte Carlo (SMC) simulations of APDs with non-uniform electric fields. The mean gain and excess noise results obtained from the SMC model employing these equations show good agreement with the results reported for a series of silicon diodes, including a p+n diode with steep electric field gradients. These results confirm the validity and demonstrate the feasibility of the trajectory tracking equations applied in SMC models for simulating mean gain and excess noise in APDs with non-uniform electric fields. Also, the simulation results of mean gain, excess noise, and carrier ionization positions obtained from the SMC model of this work agree well with those of the conventional SMC model employing the concept of a uniform electric field within a carrier free-flight. These results demonstrate that the electric field variation within a carrier free-flight has an insignificant effect on the predicted mean gain and excess noise results. Therefore, both the SMC model of this work and the conventional SMC model can be used to predict the mean gain and excess noise in APDs with highly non-uniform electric fields.

Ultrafast Plasmonic Control of Second Harmonic Generation

Efficient frequency conversion techniques are crucial to the development of plasmonic metasurfaces for information processing and signal modulation. In principle, nanoscale electric-field confinement in nonlinear materials enables higher harmonic conversion efficiencies per unit volume than those attainable in bulk materials. Here we demonstrate efficient second-harmonic generation (SHG) in a serrated nanogap plasmonic geometry that generates steep electric field gradients on a dielectric metasurface. An ultrafast control pulse is used to control plasmon-induced electric fields in a thin-film material with inversion symmetry that, without plasmonic enhancement, does not exhibit an even-order nonlinear optical response. The temporal evolution of the plasmonic near-field is characterized with ∼100 as resolution using a novel nonlinear interferometric technique. The serrated nanogap is a unique platform in which to investigate optically controlled, plasmonically enhanced harmonic generation in dielectric materials on an ultrafast time scale. This metamaterial geometry can also be readily extended to all-optical control of other nonlinear phenomena, such as four-wave mixing and sum- and difference-frequency generation, in a wide variety of dielectric materials.

High-T–low-P thermal anomalies superposed on biotite-grade rocks, Wongwibinda Metamorphic Complex, southern New England Orogen, Australia: heat advection by aqueous fluid?

The Wongwibinda Metamorphic Complex is characterised by ∼400 km2 of biotite-grade rocks with irregular, km-scale zones of cordierite-bearing high-T rock (T > 550°C). Cordierite-bearing rocks include different textures: (i) cordierite–K-feldspar–spotted hornfels; (ii) sheared cordierite–K-feldspar–augen schists; and (iii) migmatites with or without comparatively coarse garnet poikiloblasts. Integrated petrography, mineral chemistry and mineral equilibria modelling indicate metamorphic peak conditions in samples of hornfels of approximately P ≤ 250 MPa and T = 570–620°C. Two samples of sheared rock preserve peak conditions of approximately T = 670–690°C or T < 600°C and P ≤ 200 MPa, consistent with rapid cooling or variable thermal structure in the Glen Mohr Shear Zone. Electron microprobe U–Th–Pb monazite data indicate a date of 291.5 ± 1.8 Ma for the shear zone, indistinguishable from the age of Hillgrove Plutonic Suite granitoids in the complex. Monazite ages are complex in the hornfels samples that were likely, on the basis of structural relationships, metamorphosed early in the history of the Wongwibinda Metamorphic Complex (ca 300 Ma). Previous monazite dating of migmatite samples (ca 297 Ma) suggests that the metamorphic cycle was short-lived, lasting less than ca 10 m.y. Metamorphic field gradients are <15–23°C km−1 across much of the complex but locally steep (>50–100°C km−1) around the high-T rocks. Rejection of most heat sources leaves regional conductive heating as the most plausible explanation for the smooth, broad and shallow metamorphic field gradient in the biotite-grade rocks. Another mechanism of heat transfer is required to explain the local, steep metamorphic field gradients and development of high-T cordierite-bearing rocks. The spatial association of quartzite units centred within two cordierite-bearing high-T domains and an increased abundance of quartz veins above the cordierite isograd suggests heat advection by aqueous fluid locally perturbed the broad conductive heating. Fluid was channelled within shear zones and locally infiltrated nearby rocks. Variable fluid flux and strain have produced the range of different textures in cordierite-bearing rocks of the Wongwibinda Metamorphic Complex.

Microchannel plate as a novel bipolar electrode for high‐performance enrichment of anions

Microchannel plate (MCP), a high-porosity glass membrane used as an electron multiplier in analytical/scientific instruments for the detection of energetic photons and charged particles is demonstrated here as a highly effective bipolar electrode (BPE) for electrokinetic focusing of anions. Assembled between a pair of microfluidic channels filled with an electrolyte buffer and subjected to a sufficient bias potential, MCP supports faradaic reactions, owing to its semiconducting characteristics. Thousands of microcapillary tubes fused together define MCP and act in unison such that each microcapillary serves as a tiny BPE surrounding an infinitesimal element of bulk electrolyte with a large surface-area-to-volume ratio and hence performs highly effective as compared to a planar electrode inlaid into a microchannel. This performance has been validated here where concentration enrichment of a fluorescent tracer has been demonstrated at a remarkable rate of up to 175-fold/s exceeding those reported for planar BPEs. We attribute such high performance to the rapid onset of ion-depletion zone and subsequent steep field gradient, signifying the high-porosity structure of MCP as an effective BPE.

Voxel spread function method for correction of magnetic field inhomogeneity effects in quantitative gradient-echo-based MRI.

Macroscopic magnetic field inhomogeneities adversely affect different aspects of MRI images. In quantitative MRI when the goal is to quantify biological tissue parameters, they bias and often corrupt such measurements. The goal of this article is to develop a method for correction of macroscopic field inhomogeneities that can be applied to a variety of quantitative gradient-echo-based MRI techniques. We have reanalyzed a basic theory of gradient echo MRI signal formation in the presence of background field inhomogeneities and derived equations that allow for correction of magnetic field inhomogeneity effects based on the phase and magnitude of gradient echo data. We verified our theory by mapping effective transverse relaxation rate in computer simulated, phantom, and in vivo human data collected with multi-gradient echo sequences. The proposed technique takes into account voxel spread function effects and allowed obtaining virtually free from artifacts effective transverse relaxation rate maps for all simulated, phantom and in vivo data except of the edge areas with very steep field gradients. The voxel spread function method, allowing quantification of tissue specific effective transverse relaxation rate-related tissue properties, has a potential to breed new MRI biomarkers serving as surrogates for tissue biological properties similar to longitudinal and transverse relaxation rate constants widely used in clinical and research MRI.

Stress redistribution due to cracking in periodically layered composites

The stress redistribution caused by a brittle fracture of one or several layers in a bi-material periodically layered composite is considered. It is assumed that one of the composite constituents possess low crack resistance and is subject to cracking. In the case of a uniaxial tension parallel to the layering direction and in the presence of weak interfaces, the fracture pattern may be quite complicated including branching cracks. In particular, it can have the form of H-crack which is the case addressed in the present investigation. A direct numerical analysis of this problem by standard methods may be more time consuming due to the necessity to account for a relatively large number of degrees of freedom. This is required due to the fine composite microstructure and steep stress field gradients in the vicinity of the crack. Therefore a novel approach is employed which is based on the combined use of the high fidelity generalized method of cells model, the representative cell method and the higher-order theory. The crack existence is modeled by introducing fictitious unknown eigenstresses which are computed by an iterative procedure. This modeling is verified by a comparison with known analytical solution for a crack in a homogeneous plane. In addition, a verification by comparison with a known numerical solution for the special case of a transverse crack embedded in a periodically layered material is given.The influence of the volume fraction and elastic moduli ratio of the constituents as well as the H-crack aspect ratio on the stress field variation is examined, and the shielding effect of the interface cracks is quantified. The limiting situation of long interfacial cracks corresponding to the case of an incomplete layer is considered. The effect of a thermal loading on the cracked layered composite is demonstrated.

On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

Electrokinetic techniques are a staple of microscale applications because of their unique ability to perform a variety of fluidic and electrophoretic processes in simple, compact systems with no moving parts. Isotachophoresis (ITP) is a simple and very robust electrokinetic technique that can achieve million-fold preconcentration1,2 and efficient separation and extraction based on ionic mobility.3 For example, we have demonstrated the application of ITP to separation and sensitive detection of unlabeled ionic molecules (e.g. toxins, DNA, rRNA, miRNA) with little or no sample preparation4-8 and to extraction and purification of nucleic acids from complex matrices including cell culture, urine, and blood.9-12ITP achieves focusing and separation using an applied electric field and two buffers within a fluidic channel system. For anionic analytes, the leading electrolyte (LE) buffer is chosen such that its anions have higher effective electrophoretic mobility than the anions of the trailing electrolyte (TE) buffer (Effective mobility describes the observable drift velocity of an ion and takes into account the ionization state of the ion, as described in detail by Persat et al.13). After establishing an interface between the TE and LE, an electric field is applied such that LE ions move away from the region occupied by TE ions. Sample ions of intermediate effective mobility race ahead of TE ions but cannot overtake LE ions, and so they focus at the LE-TE interface (hereafter called the "ITP interface"). Further, the TE and LE form regions of respectively low and high conductivity, which establish a steep electric field gradient at the ITP interface. This field gradient preconcentrates sample species as they focus. Proper choice of TE and LE results in focusing and purification of target species from other non-focused species and, eventually, separation and segregation of sample species.We here review the physical principles underlying ITP and discuss two standard modes of operation: "peak" and "plateau" modes. In peak mode, relatively dilute sample ions focus together within overlapping narrow peaks at the ITP interface. In plateau mode, more abundant sample ions reach a steady-state concentration and segregate into adjoining plateau-like zones ordered by their effective mobility. Peak and plateau modes arise out of the same underlying physics, but represent distinct regimes differentiated by the initial analyte concentration and/or the amount of time allotted for sample accumulation.We first describe in detail a model peak mode experiment and then demonstrate a peak mode assay for the extraction of nucleic acids from E. coli cell culture. We conclude by presenting a plateau mode assay, where we use a non-focusing tracer (NFT) species to visualize the separation and perform quantitation of amino acids.

On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

Electrokinetic techniques are a staple of microscale applications because of their unique ability to perform a variety of fluidic and electrophoretic processes in simple, compact systems with no moving parts. Isotachophoresis (ITP) is a simple and very robust electrokinetic technique that can achieve million-fold preconcentration1,2 and efficient separation and extraction based on ionic mobility.3 For example, we have demonstrated the application of ITP to separation and sensitive detection of unlabeled ionic molecules (e.g. toxins, DNA, rRNA, miRNA) with little or no sample preparation4-8 and to extraction and purification of nucleic acids from complex matrices including cell culture, urine, and blood.9-12 ITP achieves focusing and separation using an applied electric field and two buffers within a fluidic channel system. For anionic analytes, the leading electrolyte (LE) buffer is chosen such that its anions have higher effective electrophoretic mobility than the anions of the trailing electrolyte (TE) buffer (Effective mobility describes the observable drift velocity of an ion and takes into account the ionization state of the ion, as described in detail by Persat et al.13). After establishing an interface between the TE and LE, an electric field is applied such that LE ions move away from the region occupied by TE ions. Sample ions of intermediate effective mobility race ahead of TE ions but cannot overtake LE ions, and so they focus at the LE-TE interface (hereafter called the "ITP interface"). Further, the TE and LE form regions of respectively low and high conductivity, which establish a steep electric field gradient at the ITP interface. This field gradient preconcentrates sample species as they focus. Proper choice of TE and LE results in focusing and purification of target species from other non-focused species and, eventually, separation and segregation of sample species. We here review the physical principles underlying ITP and discuss two standard modes of operation: "peak" and "plateau" modes. In peak mode, relatively dilute sample ions focus together within overlapping narrow peaks at the ITP interface. In plateau mode, more abundant sample ions reach a steady-state concentration and segregate into adjoining plateau-like zones ordered by their effective mobility. Peak and plateau modes arise out of the same underlying physics, but represent distinct regimes differentiated by the initial analyte concentration and/or the amount of time allotted for sample accumulation. We first describe in detail a model peak mode experiment and then demonstrate a peak mode assay for the extraction of nucleic acids from E. coli cell culture. We conclude by presenting a plateau mode assay, where we use a non-focusing tracer (NFT) species to visualize the separation and perform quantitation of amino acids.

Catch, Hold, and Release: Manipulating Single DNA Molecules in Solution

The ability to manipulate matter on submicron length scales has revolutionized biophysical research and fueled important scientific and technological advances in past decades. For example, larger dielectric particles can be trapped free in solution by steep electromagnetic field gradients produced by a strongly focused laser beam (optical tweezers).Pushing the limits to the nanometer level, however, has proven challenging. The only known method for trapping fluorescent nanoparticles such as single molecules uses a time-varying DC field in a feedback loop to counteract Brownian motion. This trap, however, can only operate when the particle can be located through fluorescence detection, which is problematic in the case of single molecules where intermittent fluorescence emission is often observed, and requires a complex hardware and software setup.In this contribution, we will discuss a novel and elegant approach for the trapping and manipulation of single molecules and other particles over extended periods of time: the electrostatic corral. The proposed trapping scheme has distinct characteristics which set it apart from other trapping techniques, such as a trapping efficiency that scales favorably with particle size (down to the single molecule level), a stable potential well that does not require any imaging for particle trapping, and multi-particle trapping capabilities. The feasibility of the corral trap approach will be demonstrated with experiments on micro- and nanoscale particles, with particular emphasis on the trapping of single-stranded DNA molecules.

High Field-Gradient Design of Single-Pole Write-Head With Planar Pole Structure

A planar single-pole head generating a large head field was investigated to improve head field distribution with a steep field gradient. Good writing performance is generally difficult for a narrow track writer. This work presents a novel design of the main pole shape, the three-step-slope, to achieve a high gradient and strong write head field for terabit recording. Furthermore, the medium design was investigated to increase head-to-medium interaction for achieving a high field gradient and narrow field distribution. A soft guard band in the recording layer and a cross-track groove on the SUL surface were effective for improving the field gradient.