Bottom Effect in Atomic Force Microscopy Nanomechanics

In this work, the influence of the rigid substrate on the determination of the sample Young's modulus, the so‐called bottom‐effect artifact, is demonstrated by an atomic force microscopy force‐spectroscopy experiment. The nanomechanical properties of a one‐component supported lipid membrane (SLM) exhibiting areas of two different thicknesses are studied: While a standard contact mechanics model (Sneddon) provides two different elastic moduli for these two morphologies, it is shown that Garcia's bottom‐effect artifact correction yields a unique value, as expected for an intrinsic material property. Remarkably, it is demonstrated that the ratio between the contact radius (and not only the indentation) and the sample thickness is the key parameter addressing the relevance of the bottom‐effect artifact. The experimental results are validated by finite element method simulations providing a solid support to Garcia's theory. The amphiphilic nature of the investigated material is representative of several kinds of lipids, suggesting that the results have far reaching implications for determining the correct Young's modulus of SLMs. The generality of Garcia's bottom‐effect artifact correction allows its application to every kind of supported soft film.     

Full-complex amplitude modulation with binary spatial light modulators

Imperfections and nonrobust behavior of practical multilevel spatial light modulators (SLMs) degrade the performance of many proposed full-complex amplitude modulation schemes. We consider the use of more robust binary SLMs for this purpose. We propose a generic method, by which, out of K binary (or 1 bit) SLMs of size M×N, we effectively create a new 2(K)-level (or K bit) SLM of size M×N. The method is a generalization of the well-known concepts of bit plane representation and decomposition for ordinary gray scale digital images and relies on forming a properly weighted superposition of binary SLMs. When K is sufficiently large, the effective SLM can be regarded as a full-complex one. Our method is as efficient as possible from an information theoretical perspective. A 4f system is discussed as a possible optical implementation. This 4f system also provides a means for eliminating the undesirable higher diffraction orders. The components of the 4f system can easily be customized for different production technologies.     

Zeroth-order phase-contrast technique

What we believe to be a new phase-contrast technique is proposed to recover intensity distributions from phase distributions modulated by spatial light modulators (SLMs) and binary diffractive optical elements (DOEs). The phase distribution is directly transformed into intensity distributions using a 4f optical correlator and an iris centered in the frequency plane as a spatial filter. No phase-changing plates or phase dielectric dots are used as a filter. This method allows the use of twisted nematic liquid-crystal televisions (LCTVs) operating in the real-time phase-mostly regime mode between 0 and p to generate high-intensity multiple beams for optical trap applications. It is also possible to use these LCTVs as input SLMs for optical correlators to obtain high-intensity Fourier transform distributions of input amplitude objects.     

A digital PN signal correlator with improved performance

Abstract

A new digital PN signal correlator, which is more suitable and easier to implement, using digital integrated circuits is proposed in this paper. This digital PN signal correlator consists of a bit matched filter, an exclusive OR operator, and a counter. The statistical properties and the error rate performance of the digital PN signal correlator are analyzed and discussed in detail. The results show that this digital PN signal correlator will suffer slight SNR degradation., (maximum degradation is about —2 dB) as compared with the conventional analog PN signal correlator for small values of E_b/N₀ (<0.75), but for high E_b/N₀, even a very significant SNR improvement can be achieved.     

Fringing fields in a liquid crystal spatial light modulator for beam steering

Abstract

Phase modulating spatial light modulators (SLMs) can be used to alter the shape of a laser wavefront to achieve a deflection or change in the shape of a laser beam. This paper reports the results of characterization, simulation and optimization of a one-dimensional liquid crystal (LC) SLM. The device has a large ratio between LC layer thickness and pixel pitch that results in a fringing field between pixels. In effect, the applied phase patterns will be lowpass filtered and the loss of high frequency components limits, for instance, the usable steering range. A method is presented where intensity measurements in the far field are used to determine how the phase modulation at the SLM is distorted. The inhomogeneous optical anisotropy of the device was determined by modelling the liquid crystal director distribution within the electrode-pixel structure. Finite-difference time-domain (FDTD) simulations were used to calculate the light propagation through the LC. The simulated phase distortion was compared with the experimental results. A voltage compensation scheme to improve the diffraction efficiency was developed utilizing the measured and simulated results. It is demonstrated that a modification of the voltage patterns can give a better realization of high frequency components in the phase distribution and an increase in maximum steering angle by a factor two.     

Formulation design,in vitro characterizations and anti-malarial investigations of artemether and lumefantrine-entrapped solid lipid microparticles

Context: Poor aqueous solubility of artemether and lumefantrine makes it important to seek better ways of enhancing their oral delivery and bioavailability.

Objective: To formulate and carry out in vitro and anti-malarial pharmacodynamic evaluations of solidified reverse micellar solutions (SRMS)-based solid lipid microparticles (SLMs) of artemether and lumefantrine for oral delivery and improved bioavailability.

Materials and methods: Rational blends of Softisan^®154 and Phospholipon^®90H lipid matrices, and different concentrations of artemether and lumefantrine were used to formulate several batches of SLMs. Drug-free SLMs were also formulated. Morphology, particle size, encapsulation efficiency (EE%) and pH studies were performed. In vitro release studies were performed in alcoholic buffer, simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) without enzymes. Anti-malarial pharmacodynamic studies were conducted in mice.

Results: Stable, smooth and spherical particles with sizes ranging from 4.2?±?0.02 to 9.3?±?0.8?µm were formed. EE% of 92.2–97.3% and 30.2–84.7% and pH of 3.0?±?0.02 to 4.9?±?0.12 and 3.0?±?0.02 to 5.8?±?0.05 were obtained for artemether and lumefantrine SLMs, respectively. Release of 100, 88.28 and 75.49%, as well as 63.26, 34.31 and 56.17% were recorded for artemether and lumefantrine in alcoholic buffer, SGF and SIF, respectively. Pharmacodynamic studies indicated very significant (p?Conclusion: Oral delivery and bioavailability of artemether and lumefantrine could be improved using SRMS-based SLMs.     

Diffraction-based determination of the phase modulation for general spatial light modulators

We describe a characterization method based on diffraction for obtaining the phase response of spatial light modulators (SLMs), which in general exhibit both amplitude and phase modulation. Compared with the conventional interferometer-based approach, the method is characterized by a simple setup that enables in situ measurements, allows for substantial mechanical vibration, and permits the use of a light source with a fairly low temporal coherence. The phase determination is possible even for a SLM with a full amplitude modulation depth, i.e., even if there are nulls in the amplitude transmission characteristic of the SLM. The method successfully determines phase modulation values in the full 2pi rad range with high accuracy. The experimental work includes comparisons with interferometer measurements as well as a SLM characterization with a light-emitting diode (LED).     

Convergent optical correlator aligment based on frequency filtering

The convergent correlator is widely used but it presents the drawback of the alignment requirements: fine focusing of the input scene Fourier transform on the filter plane, filter centering, scaling the scene Fourier transform to match the filter size, and azimuth matching of the filter with the input scene. We propose a set of tests to obtain a precise alignment of the convergent correlator. These methods are based on frequency filtering properties and they are applicable either for amplitude input or for phase-encoded input. The tests we present allow us to fulfill all the alignment requirements. The theory on which these tests are based is explained. The experimental results obtained during the alignment procedure are presented. We show some additional verifications of the correct alignment of the convergent correlator.     

Analysis of spatial light modulator contrast ratios and optical correlation

We have performed a general analysis of optical correlators with spatal light modulators (SLM's) whose primary defect is a finite contrast ratio (CR). Our mathematical analysis identifies three noise terms that appear in addition to the correlation term. The filter SLM contains either a phase-only filter (POF) or a binary-phase-only filter (BPOF). Insertion of a dc block at the center of the filter SLM decreases the noise background in the correlator plane; this dc block is larger than that required for the same level of performance in a correlator whose SLM's have transmissive (or reflective) dead zones. With a noise-free input and the dc block, our computer simulations that show the peak intensity falling off as the CR decreases are in quantitative agreement with the correlation term of the mathematical model. For a cluttered, disjoint noise input this agreement is only qualitative, and at low CR's the dc block is definitely required for the BPOF correlator if the secondary peaks in the output are to be brought below the correlation peak.     

Fast digital hologram generation and adaptive force measurement in liquid-crystal-display-based holographic tweezers

Computer-generated holograms in conjunction with spatial light modulators (SLMs) offer a way to dynamically generate holograms that are adapted to specific tasks. To use the full dynamic capability of the SLM, the hologram computation should be very fast. We present a method that uses the highly parallel architecture of a consumer graphics board to compute analytical holograms in video real time. A precice characterization of the SLM (Holoeye LC-R-2500) and the adaption of its settings to our near-infrared application is necessary to guarantee an efficient hologram reconstruction. The benefits of a fast computation of adapted holograms and the application of an efficient SLM are demonstrated by measuring the trapping forces of holographic tweezers.     

Anamorphic Multiple Matched Filter for Character Recognition,Performance with Signals of Equal Size

Abstract

The construction and performance of an anamorphic multiple matched filter for character recognition is presented, in the usual situation of characters of equal input size and having the same size in the target. So a simple anamorphic correlator can be employed to obtain the recognition of a given character. In order to avoid false alarms the characters in the target are rotated by different angles depending on the angular tolerance of the correlator, which is rotationally variant and smaller than in symmetrical systems within a certain angular region. Thus the number of signals to which the filter can be matched can be greater than with spherical optics correlators.     

Modulation transfer function measurement method for electrically addressed spatial light modulators

The modulation transfer function (MTF), when used with amplitude modulation (m(A)) data, is a vital coherent optical performance measure for a spatial light modulator (SLM). A new image plane amplitude MTF (MTF(A)) measurement method is presented for electrically addressed SLMs. It involves digital analysis of the output image of a square-wave pattern written onto the SLM. Modulation-level effects are also addressed. Optical laboratory results are presented for two liquid-crystal SLMs. The need to consider amplitude rather than intensity modulation (when coherent optical processing applications are considered) is noted in terms of SLM biasing.     

Experimental systems implementation of a hybrid optical-digital correlator

A high-speed hybrid optical-digital correlator system was designed, constructed, modeled, and demonstrated experimentally. This correlator is capable of operation at approximately 3000 correlations/s. The input scene is digitized at a resolution of 512 x 512 pixels and the phase information of the two-dimensional fast Fourier transform calculated and displayed in the correlator filter plane at normal video frame rates. High-fidelity reference template images are stored in a phase-conjugating optical memory placed at the nominal input plane of the correlator and reconstructed with a high-speed acousto-optic scanner; this allows for cross correlation of the entire reference data set with the input scene within one frame period. A high-speed CCD camera is used to capture the correlation-plane image, and rapid correlation-plane processing is achieved with a parallel processing architecture.     

The impact of particle preparation methods and polymorphic stability of lipid excipients on protein distribution in microparticles

Objective: The present study aimed at elucidating the influence of polymorphic stability of lipid excipients on the physicochemical characters of different solid lipid microparticles (SLM), with the focus on the alteration of protein distribution in SLM.

Methods: Labeled lysozyme was incorporated into SLM prepared with different excipients, i.e. trimyristin (TG14), glyceryl distearate (GDS), and glyceryl monostearate (GMS), by water-oil-water (w/o/w) or solid-oil-water (s/o/w) method. The distribution of lysozyme in SLM and the release of the protein from SLM were evaluated by confocal laser scanning microscopy. The storage stability of SLM was characterized by HPLC, differential scanning calorimetry, X-ray powder diffraction, and scanning electron microscopy.

Results: Lysozyme was displayed as small scattered domains inside GDS and GMS SLM, whereas it was incorporated in the core of TG14 SLM formulated by the w/o/w method or evenly distributed in TG14 SLM prepared by the s/o/w method. Stability study at 37?°C revealed that only TG14 SLM made by the w/o/w method was able to maintain the lysozyme amount both on the particle surface and released from the SLM. Elevated storage temperature induced polymorphic transition of lipids in GDS and GMS SLM, which was, however, not remarkable for the TG14 SLM.

Conclusions: Lipid excipients and particle preparation methods were found to differently affect the lysozyme distribution in SLM, owning to varied storage stabilities of the lipids. The present study provides updated knowledge for rational development of lipid-based formulations for oral delivery of peptide or protein drugs.     

Notched fatigue testing of Inconel 718 prepared by selective laser melting

Selective laser melting (SLM) was used to prepare notched high‐cycle fatigue test specimens made from nickel‐based superalloy Inconel 718. Samples were designed to have 1 of 3 different notch geometries, including V notches with K_t of 2.2 or 3.1, a U notch with K_t of 2.0, and were printed in either vertical or horizontal orientations. Samples were tested with as‐printed dimensions and surfaces after heat treatment, but a separate set of SLM samples were printed as plates and machined to final dimensions comporting to the V‐notch specimen with K_t = 3.1. High‐cycle fatigue testing showed that machined SLM specimens behaved similar to wrought Inconel 718 plate specimens, but testing with as‐produced surfaces led to a decrease in fatigue life. The explanation for this difference is based on approximations of linear elastic fracture mechanics solutions for short cracks emanating from notch roots, with intrinsic surface features of SLM materials serving as the cracks. Analysis of the actual notch geometries after SLM fabrication indicates that stress intensity in the presence of these features plays a prominent role in determining number of cycles before fatigue crack initiation and propagation occurs.     

Multiple-target detection with use of a modified amplitude-modulated joint transform correlator

Multiple-target detection with a modified amplitude-modulated joint transform correlator is proposed. With this technique the joint power spectrum is first modified by the subtraction of the power spectrum of the input scene only and of the reference image from it; the resultant modified joint power spectrum is next multiplied by the amplitude-modulated filter function. The effect of noise in the input scene on the performance of the joint transform correlator is analyzed and quantified. This technique is found to deliver a correlation output and the capacity to accommodate noise in the input scene better than both the fringe-adjusted filter-based joint transform correlator and the modified fringe-adjusted filter-based joint transform correlator.     

Optical angular correlation in fourier domain

Abstract

The angular correlation of Fourier spectra is optically implemented by means of a single Fourier transformer. Fourier-domain-based angular correlation, which is a technique specific to periodic pattern recognition and characterization, is efficiently applied in real time to ordinary textile structures. By introducing scale corrections, either isomorphic or anamorphic, the optical system is capable of recognizing different structures of the same sort of fabric even when the fundamental frequencies—or thread densities—do not coincide. Two possible methods to introduce the information into the input image of the optical angular correlator are considered: an opto-mechanical rotator containing a transparency with the input sample image; and an electronic addressed spatial light modulator that displays the input sample image controlled by computer. Experimental results of both possibilities are presented and discussed.     

Modified fringe-adjusted joint transform correlation to accommodate noise in the input scene

A modified fringe-adjusted joint transform correlator is proposed that is able to accommodate noise in the input scene. The effect of noise in the input scene on the performance of the joint transform correlator is analyzed and quantified. When the target is embeddedin aseverely noise-corrupted input scene, it is shown that the proposed modified fringe-adjusted filter joint transform correlator delivers a better correlation performance and the capacity to accommodate this noise than does the fringe-adjusted filter-based correlator. When the power spectra of the input image and the reference image are subtracted from the power spectrum of the joint-input image, it is found that the noise effect on the output plane is independent of the objects in the input scene and originates from the convolution of the reference image and noise in the input scene.     

Suppression of the zero-order diffracted beam from a pixelated spatial light modulator by phase compression

Phase compression is used to suppress the on-axis zero-order diffracted (ZOD) beam from a pixelated phase-only spatial light modulator (SLM) by a simple modification to the computer generated hologram (CGH) loaded onto the SLM. After CGH design, the phase of each SLM element is identically compressed by multiplying by a constant scale factor and rotated on the complex unit-circle to produce a cancellation beam that destructively interferes with the ZOD beam. Experiments achieved a factor of 3 reduction of the ZOD beam using two different liquid-crystal SLMs. Numerical simulation analyzed the reconstructed image quality and diffraction efficiency versus degree of phase compression and showed that phase compression resulted in little image degradation or power loss.     

Designing discriminative spatial filter vectors in motor imagery brain–computer interface

The problem of a volume conduction effect in electroencephalography is considered one of the challenging issues in brain–computer interface (BCI) community. In this article, we propose a novel method of designing a class‐discriminative spatial filter assuming that a combination of spatial pattern vectors, irrespective of the eigenvalues of the common spatial pattern (CSP), can produce better performance in terms of classification accuracy. We select discriminative spatial filter vectors that determine features in a pairwise manner, that is, eigenvectors of the K largest eigenvalue and the K smallest eigenvalue. Although the pair of the eigenvectors of the K largest and the K smallest eigenvalues helps extract discriminative features, we believe that a different set of eigenvector pairs is more appropriate to extract class‐discriminative features. In our experimental results using the publicly available dataset of BCI Competition IV, we show that the proposed method outperformed the conventional CSP methods and a filter‐bank CSP. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 147–151, 2013