Fabrication of magnetic micro- and nanostructures by scanning probe lithography

Planar magnetic structures based on cobalt nanofilms have been obtained by scanning probe lithography. It has been shown that ferromagnetic nanoparticles with different domain structures can be formed by local oxidation of a cobalt film on a graphite substrate with the use of a conductive probe of an atomic force microscope (AFM). Using AFM nanoengraving of polymethylmethacrylate, masks were formed to obtain microcontact pads connected by cobalt nanowires with a width of 250–1400 nm and a thickness of 10–30 nm on the silicon dioxide surface. The topography and magnetization structure of the obtained samples were controlled by atomic and magnetic force microscopy.     

Stability of magnetooptical disks under the action of external magnetic fields

The stability of data recorded on magnetooptical disks of different manufacturers is investigated under external magnetic fields oriented along the normal to the disk surface. The recorded data are found to be damaged under magnetic fields with intensities ranging from 300 to 350 kA/m. However, such disks can be reused for information recording. Under the action of magnetic fields with intensities more than 420 kA/m, information on disks is lost and they cannot be reused.     

Computation of the magnetic polarizability of conducting disks and the electric polarizability of apertures

The electric polarizability of a small aperture of arbitrary shape is computed by solving the dual magnetostatic problem of a conducting disk. The method of moments is used to solve the integral equation for the current density induced on the disk. Charge-free expansion functions for the current density are introduced. The electric polarizability of the aperture is obtained from the magnetic polarizability of a complementary disk through the use of the duality principle. Results for five typical aperture shapes including the circle and ellipse are computed. The results of the computations are compared with available exact or measured data, and they show good agreement.     

A study of the magnetic characteristics of permalloy nanostructures by micromagnetic simulation

The dependence of the magnetic characteristics of permalloy nanostructures on their sizes has been studied by the micromagnetic simulation method. The critical size of a square-shaped nanoisland for transition into a single-domain state has been estimated. The dependence of the coercive force of the nanoisland on its thickness and area has been studied.     

Holes localized in nanostructures in an external magnetic field: g-factor and mixing of states

Semiconductors - The energy spectrum and wave functions of holes in the valence band in semiconductor nanosystems, including quantum wells, quantum wires, and quantum dots, in an external magnetic...     

A quantized delay-lock discriminator

A new quantized delay-lock discriminator is described which uses fixed delay lines that are switched in and out, depending upon the output of a correlator. Two versions of the system, with analog-to-digital feedback and relay feedback, are discussed. Some experimental results are also included.     

Characterization of a new cobalt precursor for focused beam deposition of magnetic nanostructures

The electrical and magnetic properties of nanowires deposited from cobalt tricarbonyl nitrosyl (Co(CO)₃NO) precursor by focused electron beam- and focused ion beam-induced deposition (FEBID and FIBID) have been investigated. As-deposited nanowires have similar Co content, around 50-55 at.%, but different electrical behaviour: FEBID nanowire is highly resistive (6.3 mΩ cm at RT) and non-metallic at low T, while the FIBID one has much lower resistivity (189 μΩ cm at RT) and it is metallic. The magnetic properties, tested with magnetoresistance measurements, reveal a non-magnetic behaviour for both nanowires. After 400 °C annealing in vacuum FEBID wire is much less resistive (62 μΩ cm at RT) and recovers the metallic behaviour at low T, and both FEBID and FIBID wires display ferromagnetic behaviour. Structural analysis by low energy-scanning transmission electron microscopy (LE-STEM) suggests that coarsening and interconnection of the Co nanograins are responsible for the improvement in electrical and magnetic properties.     

Enhancement of InGaN-Based Vertical LED With Concavely Patterned Surface Using Patterned Sapphire Substrate

To improve the external quantum efficiency, we have proposed a new method utilizing surface roughening of vertical-type light-emitting diodes (VT-LEDs) fabricated on hemispherical patterned sapphire substrate by using a laser lift-off technique. The advantages of this method are simple and reproducible in transferring the well-defined patterns on sapphire into GaN layer. The VT-LED with concavely patterned surface showed a nearly twofold increase in the output power compared to the normal planar surface. This improvement in the VT-LED performances is attributed to the increase in the escaping probability of photons from the LED surface.     

Turbo decoding of quantized data

Much of the work on turbo decoding assumes that the decoder has access to infinitely soft (unquantized) channel data. In practice, however, a quantizer is used at the receiver and the turbo decoder must operate on finite precision, quantized data. Hence, the maximum a posteriori (MAP) component decoder which was designed assuming infinitely soft data is not necessarily optimum when operating on quantized data. We modify the well-known normalized MAP algorithm taking into account the presence of the quantizer. This algorithm is optimum given any quantizer and is no more complex than quantized implementations of the MAP algorithm derived based on unquantized data. Simulation results on an additive white Gaussian noise channel show that, even with four bits of quantization, the new algorithm based on quantized data achieves a performance practically equal to the MAP algorithm operating on infinite precision data     

FIR differentiators for quantized signals

The impact of quantization noise on a signal whose rate is to be estimated using a FIR differentiator is analyzed, concentrating on the important constant-rate case in order that the filter be optimized for systems with low-frequency rates of change. Formulae for the mean-squared error of the filter, the corresponding spectral characteristics, and general formulae governing the filter coefficients are derived. The characteristics of four specific differentiators, including a representative wideband differentiator, are examined and compared. It is shown that a differentiator that is optimum in terms of its attenuation of white noise can also be considered optimum with respect to quantization noise attenuation in certain circumstances. An elegant relationship is derived between worst-case RMS error and the fractional value of the rate at which this error occurs. Minimization of this worst-case mean-squared error is shown to be achieved with a simple differentiator. However, the corresponding average error is poor, and a simple nonlinear filter that minimizes the worst-ease error, while retaining a similar average mean-squared error to that of the “optimum” differentiator, is proposed. The equivalence between FIR differentiators and the decoders used in single-loop sigma-delta modulators is also highlighted     

量子化电学标准综述

基于约瑟夫森效应的电压标准与基于量子霍尔效应的电阻标准是两项基本的量子化电学标准,为推进计量量子化的发展和普及,本文对这两个标准的物理学原理与基本状况分别做简要介绍。     

Patterned Arrays of Supramolecular Microcapsules

Micropatterning of hydrogel has brought innovative outcomes in fundamental and applied material sciences. Previous approaches have mainly been dedicated to fabricate arrays of bulk hydrogel beads, which have inherent challenges including loading ability, scalability, specificity, and versatility. Here, a methodology is presented to create hollow microcapsule arrays from sessile microdroplets. The difference in wettability between hydrophilic and hydrophobic surfaces enables self‐partitioning of liquid into microdroplet arrays, serving as microreservoirs to load complementarily functionalized host–guest polymers, cucurbit[8]uril‐threaded highly branched polyrotaxanes (HBP‐CB[8]) and naphthyl‐functionalized hydroxyethyl cellulose (HEC‐Np). The interfacial dynamic complexation between positively charged HBP‐CB[8] and HEC‐Np occurs in the presence of negatively charged surfactants, resulting in condensed supramolecular hydrogel skins. The hydrogel microcapsules are uniform in size and are developed to encapsulate target cargos in a robust and well‐defined manner. Moreover, the microcapsule substrates are further used for surface enhanced Raman spectroscopy sensing upon loading of gold nanoparticles. This facile assembly of microcapsule arrays has potential applications in controlled cargo delivery, bio‐sensing, high‐throughput analysis, and sorting.     

Stability of the quantized LMS algorithm

The least mean square (LMS) algorithm is investigated for stability when implemented with two's complement quantization. The study is restricted to algorithms with periodically varying inputs. Such inputs are common in a variety of applications, and for system identification, they can always be generated as shown with an example. It is shown that the quantized LMS algorithm is just a special case of a quantized periodically shift-varying (PSV) filter. Two different sufficient conditions are obtained for the bounded input bounded output (BIBO) stability of the PSV filter. When the filter is BIBO stable, two different bounds on the filter output are also derived. These conditions and bounds are then applied to the quantized LMS algorithm. The results are illustrated with examples.     

Stealing bits from a quantized source

We consider "bit stealing" scenarios where the rate of a source code must be reduced without prior planning. We first investigate the efficiency of source requantization to reduce rate, which we term successive degradation. We focus on finite-alphabet sources with arbitrary distortion measures as well as the Gaussian-quadratic and high-resolution scenarios. We show an achievable rate-distortion tradeoff and prove that this is the best guaranteeable tradeoff for any good source code. This tradeoff is in general different from the rate-distortion tradeoff with successive refinement, where there is prior planning. But, we show that with quadratic distortion measures, for all sources with finite differential entropy and at least one finite moment, the gap is at most 1/2 bit or 3 dB in the high-resolution limit. In the Gaussian-quadratic case, the gap is at most 1/2 bit for all resolutions. We further consider bit stealing in the form of information embedding, whereby an embedder acts on a quantized source and produces an output at the same rate and in the original source codebook. We develop achievable distortion-rate tradeoffs. Two cases are considered, corresponding to whether or not the source decoder is informed of the embedding rate. In the Gaussian-quadratic case, we show the informed decoder need only augment the regular decoder with simple post-reconstruction distortion compensation in the form of linear scaling for the resulting system to be as efficient as bit stealing via successive degradation. Finally, we show that the penalty for uninformed versus informed decoders is at most 3 dB or 0.21-bit in the Gaussian-quadratic case and that their performance also lies within the 1/2-bit gap to that of successive refinement.     

Optical disks become erasable

The characteristics of advantages of magneto-optical storage are discussed. The way in which such disks are written, read, and erased is described. The use of optical disks for image processing is examined. Also considered are the materials that made the technology practical; expected improvements in data rates; the lagging development of drives; and the anticipated increase in capacity     

Performance analysis of sign quantized projection

Quantized projection technology(QP) is the version of quantization index modulation(QIM) working in the projection domain.It essentially belongs to a double-sided additive embedder.In this article,the concept of sign quantized projection(SQP) is proposed,which differs from the conventional QP when working as a single-sided embedder.Theoretical analysis reveals that SQP has the same probability of miss and probability of false alarm as QP.Also,the document-to-watermark ratio(DWR) of SQP is less than its coun...     

钛酸和铌酸纳米结构的合成、表征和形成机制

自碳纳米管发现以来，纳米管、纳米线等纳米结构的研究受到广泛重视。钛酸和铌酸是半导体，有光催化和离子交换特性，可用于气体传感器，能量转换和环境净化等，由这些材料组成的纳米材料有可能成为很好的纳米器件。本文工作中，我们合成了这类层状化合物的多种纳米管、纳米线、纳米带和纳米片。     

Design and analysis of quantized controllable doped left-handed materials

Two kinds of controllable doped left-handed materials (DLHMs) were designed by inserting inductors and capacitors into the traditional left-handed material (LHM) as heterogeneous elements respectively,which are DLHM with inductors (LDLHM) and DLHM with capacitors (CDLHM).The characteristics of transmission spectrum were studied by using finite-difference time-domain method (FDTD).Compared with the traditional LHM,the resonance strength of the LDLHM is weakened and the pass-band is narrowed,but with the increase of the value of the inserted inductors,the bandwidth is expanded.As capacitors inserted into the LHM,the pass-band of the CDLHM is expanded,but the pass-band is shifted to low frequency and the bandwidth is narrowed with the increase of the value of the capacitors,meanwhile,a new generated pass-band is also shifted to low frequency.Therefore,a quantized controllable doped left-handed material can be achieved.