Log-polar transform-based wavelet-modified maximum average correlation height filter for distortion-invariant target recognition

In this paper, we report a log-polar transform-based filter for in-plane rotation and scale-invariant target recognition. The log-polar transform is a known space-invariant image representation used in several image vision systems to eliminate the effects of scale and rotation in an image. In case of in-plane rotation invariance, peaks shift horizontally, while in case of scale invariance, peaks shift vertically. For full out-of-plane rotation-invariance (0–360°), log-polar transformed images are used to train the wavelet-modified maximum average correlation height (WaveMACH) filter. Correlation peak height and peak-to-sidelobe ratio have been calculated as metrics of goodness of the log-polar transform-based WaveMACH filter. This filter would reduce the memory requirement for filter storage in a practical system. Simulation results have been presented.     

Spectral band invariant wavelet-modified MACH filter

Filters synthesized with images of a specific spectral band in general fail to recognize targets in a different spectral band. In this paper, we therefore demonstrate the use of the wavelet-modified maximum average correlation height (WaveMACH) filter for automatic target recognition applications in both the visible and infrared (IR) spectral bands. As any input target appears different when imaged through two different sensors, i.e., a CCD or an IR camera, a WaveMACH filter synthesized using a CCD image shows no correlation with the image of the same target from an IR camera and vice-versa. Hence, separate filters are required to match the input targets from the two sensors. To avoid the synthesis and storage of separate filters, the images from CCD and IR camera are fused using Daubechies wavelet and then the rotation-invariant WaveMACH filter generated with the fused image. In all, 18 WaveMACH filters (each of 20° range) are required for in-plane rotation invariance in both the spectral bands for the full range of 0–360°. Computer simulation and experimental results implemented in hybrid digital–optical correlator architecture are shown for the proposed idea. The same filters have also been used to identify multiple targets in a scene. Performance measures like peak-to-sidelobe ratio (PSR), peak correlation energy (PCE) and correlation peak intensity (CPI) have been calculated as metrics of goodness.     

Echo-Planar Imaging of Porous Media with Spatial Resolution below 100 μm

A modified version of the echo-planar imaging technique incorporating a Carr–Purcell train of 180° rf pulses (PEPI) has been implemented on a standard spectrometer. It is demonstrated that artifacts in the image due to cumulative errors in the rf field can be reduced by replacing each 180° pulse by a composite sequence of three rf pulses. Artifact-free 3D images at 94 μm voxel resolution are obtained within 15 min. This technique has been applied to study the drying process in an initially water-saturated model porous medium with characteristicT^*₂of order 700 μs.     

Microwave spectrum, structure, dipole moment, and internal rotation of fluoromethyl methyl ether

Microwave spectra of fluoromethyl methyl ether and its 10 isotopically substituted species were measured. The r_s structure of this molecule was determined from the observed moments of inertia. Structural parameters obtained for this molecule, which was in the gauche form, were compared with those of the analogous molecules. Dipole moments of the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment is 1.744 ± 0.029 D making an angle of 100°54′ with the O---CH₂ bond toward the C---F direction and lies in the plane whose dihedral angles with the FCO and COC planes are 114°9′ and 44°56′, respectively. The barrier to internal rotation of the methyl group was calculated taking into account the coupling effect with the skeletal torsion using the observed splitting data of the spectra in the ground, first excited methyl torsional, and skeletal torsional states. The barrier, skeletal torsional frequency, and coupling term were determined to be V₃ = 1538 ± 40 cal/mole, ω_t = 158 ± 4 cm⁻¹, and V_s = 490 ± 500 cal/mole, respectively.     

Frequency multiplexed DOG filter

In order to improve optical correlation performance, a multiplexed DOG (MDOG) filter is constructed from two Difference of Gaussian (DOG) filters, one DOG filter is tuned for noise robustness and the other for accurate object localization. The filter's performance is compared with the CMF, POF and single DOG filter.     

Control of susceptibility-related image contrast by spin-lock techniques

Macroscopic magnetic field inhomogeneities might lead to image distortions, while microscopic field inhomogeneities, due to susceptibility changes in tissues, cause spin dephasing and decreasing T₂ relaxation time. The latter effects are especially observed in the trabecular bone and in regions adjacent to air-containing cavities when gradient-echo sequences are applied. In conventional MRI, these susceptibility-related signal voids can be avoided by applying spin-echo (SE) techniques. In this study, an alternative method for the examination and control of susceptibility-related effects by spin-lock (SL) radiofrequency pulses is presented: SL pulses were applied in two different susceptibility-sensitive sequence types: (a) between the jump and return 90° pulses in a 90°_x−τ−90°_−x magnetization-prepared Fast Low Angle Shot (FLASH) sequence and (b) between the 90° pulse and the 180° pulse in an asymmetric SE sequence. The range of Larmor frequencies used for spin locking can be determined for different B₁ amplitudes of the SL pulses, allowing control of image contrast by the amplitude of the SL pulses.     

Rotational absorption spectrum of methylene fluoride in the 20–100 cm region

The pure rotational spectrum of CH₂F₂ was recorded in the 20–100 cm⁻¹ spectral range and analyzed to obtain rotation and centrifugal distortion constants. Analysis of the data yielded rotation constants: A = 1.6392173 ± 0.0000015, B = 0.3537342 ± 0.00000033, C = 0.3085387 ± 0.00000027, τ_aaaa = −(7.64 ± 0.46) × 10⁻⁵, τ_bbbb = −(2.076 ± 0.016) × 10⁻⁶, τ_cccc = −(9.29 ± 0.12) × 10⁻⁷, T₁ = (4.89 ± 0.20) × 10⁻⁶, and T₂ = −(1.281 ± 0.016) × 10⁻⁶cm⁻¹.     

Carrier diffusion in InGaAs/GaAs quantum wells grown on vicinal GaAs(0 0 1) substrates

We have investigated the influence of vicinal GaAs substrates on the optical and electronic properties of InGaAs/GaAs quantum wells (QWs). A single In_0.10Ga_0.90As QW was grown by molecular-beam epitaxy on a vicinal GaAs(0 0 1) substrate with a miscut angle of 0° (nominal), 2°, 4° and 6° towards [1 1 0]. The carrier diffusion was obtained by a micro-photoluminescence scan technique that permits to observe the effective diffusion length characterized by the lateral spread of carriers in the QW followed by radiative recombination. The carrier diffusion length was obtained parallel (L_||) and perpendicular (L) to the atomic steps. The diffusion length decreases as the temperature increases up to 100 K. Above this temperature we found different behaviours that depend on the sample miscut angle.     

Microwave spectrum, structure, and dipole moment of the trans-trans isomer of methylpropylether

Microwave spectra of the trans-trans (TT) isomer of methylpropylether and its 12 isotopically substituted species were measured. The r_s structure of this isomer was determined from the observed moments of inertia. Structural parameters of this isomer were roughly equal to those of the reported r_s structures of trans-ethylmethylether and propane. Dipole moments of the TT isomer for the normal and two deuterated species were determined by Stark-effect measurements. For the normal species, the dipole moment was μ_a = 0.082 ± 0.010, μ_b = 1.104 ± 0.013, and μ_total = 1.107 ± 0.013 D making angles of 4°17′ with the b-inertial axis, of 6°7′ with the bisector of the COC angle. The barrier to internal rotation of the CH₃C group was calculated to be 3300 ± 60 cal/mole from A-A splittings of the spectra in the CH₃C excited torsional state.     

基于光学子波变换的SDF匹配滤波器

提出了一种基于光学子波变换的综合判别函数匹配滤波器(WFSDF),将光学子波变换和综合判别函数相结合,只用一个简单的4f系统就能实现输入图像和SDF子波变换的相关运算。采用计算全息的方法制作复数匹配滤波器。计算机模拟仿真结果表明,与传统的SDF匹配滤波器相比,WFSDF匹配滤波器,锐化了相关峰,提高了识别率,同时简化了光路,能够实现多目标的畸不变识别。     

Enhancing the capabilities of binary phase only filter

In this paper, we demonstrate that the capabilities of a binary phase-only filter (BPOF) can be enhanced to identify targets irrespective of rotation, scale or the imaging spectral band by utilizing the concept of log-polar transform and image fusion. Till date, BPOFs have been considered to be the simplest of all filters and incapable of identifying distorted images or images of different spectral bands like the visible or infrared (IR) bands. The novelty of this work lies in the approach adopted to demonstrate that a BPOF is equally capable of distortion-invariance like any other distortion-invariant complex matched filter. This is done by suitably fusing the images of visible and IR bands and then taking the log-polar transformation of the fused image to synthesize the BPOF. A single BPOF is thus sufficient to identify (0-360)° in-plane rotated images, (50-190)% scaled images, combination of rotation and scale changes of the target, noisy image of both the visible and IR spectral bands. A further enhancement of the correlation peak intensity (CPI) is achieved by modifying this BPOF with Mexican-hat wavelet. The designed filter was implemented in the hybrid digital-optical correlation scheme. Correlation peak intensity and peak correlation energy (PCE) have been calculated as metrics of goodness of the proposed approach. Experimental results have been presented.     

One- and two-dimensional C–H/N–H dipolar correlation experiments under fast magic-angle spinning for determining the peptide dihedral angle φ

A recently proposed ¹³C–¹H recoupling sequence operative under fast magic-angle spinning (MAS) [K. Takegoshi, T. Terao, Solid State Nucl. Magn. Reson. 13 (1999) 203–212.] is applied to observe ¹³C–¹H and ¹⁵N–¹H dipolar powder patterns in the ¹H–¹⁵N–¹³C–¹H system of a peptide bond. Both patterns are correlated by ¹⁵N-to-¹³C cross polarization to observe one- or two-dimensional (1D or 2D) correlation spectra, which can be simulated by using a simple analytical expression to determine the H–N–C–H dihedral angle. The 1D and 2D experiments were applied to N-acetyl[1,2-¹³C,¹⁵N] -valine, and the peptide φ angle was determined with high precision by the 2D experiment to be ±155.0°±1.2°. The positive one is in good agreement with the X-ray value of 154°±5°. The 1D experiment provided the value of φ=±156.0°±0.8°.     

Effect of lower growth temperature on C incorporation in GeC epilayers on Si(0 0 1) grown by MBE

Effect of lower growth temperature T_s on C incorporation to substitutional sites in Ge_1−xC_x/Si(0 0 1) grown by molecular beam epitaxy was investigated. To enhance the non-equilibrium growth condition, the temperature T_s was lowered from 600°C down to 300°C. The C incorporation into substitutional sites of GeC epilayers was very sensitive to T_s. X-ray diffraction (XRD) measurement indicated that the substitutional C composition x increased with decrease in T_s from 600°C to 400°C. At T_s350°C, the estimation of x by the XRD analysis was impossible because of polycrystallization. The Raman shift measurement enables to estimate x for T_s350°C, as consequently larger x than that grown at T_s=400°C was verified. The enhancement of non-equilibrium growth condition by decreasing T_s was important to increase x.     

Luminescence from ZnO/MgO nanoparticle structures prepared by solution techniques

The optical and structural properties of mixed ZnO/MgO particles prepared by solution techniques are investigated by the cathodoluminescence and electron microscopy techniques. The samples annealed at 400–1000 °C show well crystalline wurtzite structure of the ZnO (MgZnO) particles with the size in range of 10–100 nm. Annealing at high temperatures (>700 °C) leads to Mg diffusion in ZnO and Mg_xZn_1−xO alloy formation. The blue shifts of the near-band-edge emission as a result of the alloy band gap widening and quantum confinement effect for the small size particles are demonstrated.     

Thermally Stimulated Luminescence (TSL) and Conductivity (TSC) of synthetic crystalline quartz

A comparative and simultaneous study of TSL and TSC above room temperature (20–400°C) has been performed on “as-grown” and “hydrogen-swept” synthetic quartz crystals. Following X- irradiations, TSL spectra (heating RATE = 1°C/s) feature a number of peaks: at 75°C an intense structure is observed (the well-known “100°C” peak of quartz); the analysis of this peak obtained by numerical methods has shown that it follows monomolecular kinetics, giving a value of 0.83 eV for the trap depth. Additional peaks are observed at 110°C and 160°C, followed by weaker and less resolved emissions above 200°C. TSC peaks at 80°C, 120°C and 160°C, particularly evident in as-grown samples when measured with the electric field applied along the x-axis, can be associated to the corresponding TSL peaks. However, spectra performed with the electric field applied along the z-axis evidence different features. In as-grown samples a strong and broad peak at approximately 132°C is observed, while hydrogen-swept samples are characterized by two peaks at 180°C and 275°C. Such an anisotropic character, and the fact that no TSL structures are observed in the same temperature range, support the hyporthesis of an ionic nature for the latter peaks. TSC “pre-dose” measurements of the 75°C peak show that no current enhancement is observed upon irradiational and heating treatment: this result is in accordance with previous radioluminescence and thermally stimulated exoelectron emission experiments and supports the proposed model of the dynamics of this effect.     

Effect of deposition period on structural and optical properties of InGaAs/GaAs quantum dots formed by InAs/GaAs short-period superlattices

Structural and optical properties of In_0.5Ga_0.5As/GaAs quantum dots (QDs) grown at 510 °C by atomic layer molecular beam epitaxy technique are studied as a function of n repeated deposition of 1-ML-thick InAs and 1-ML-thick GaAs. Cross-sectional images reveal that the QDs are formed by single large QDs rather than closely stacked InAs QDs and their shape is trapezoidal. In the image, existence of wetting layers is not clear. In 300 K-photoluminescence (PL) spectra of InGaAs QDs (n=5), 4 peaks are resolved. Origin of each peak transition is discussed. Finally, it was found that the PL linewidths of atomic layer epitaxy (ALE) QDs were weakly sensitive to cryostat temperatures (16–300 K). This is attributed to the nature of ALE QDs; higher uniformity and weaker wetting effect compared to SK QDs.     

Fast low-angle positive contrast steady-state free precession imaging of USPIO-labeled macrophages: theory and in vitro experiment

The feasibility of imaging macrophages labeled with ultrasmall superparamagnetic iron-oxide nanoparticles (USPIO) with fast low-angle positive contrast steady-state free precession (FLAPS) was investigated through theory and in vitro experiment. Human macrophage cells were labeled with USPIO and imaged at 1.5 T. The metric “visibility,” which combines magnitude and spatial extent of positive contrast, was used to evaluate the images. Negative contrast steady-state free precession (SSFP) and gradient-echo (GRE) imaging were also evaluated. Positive contrast was observed for relatively high concentrations of labeled cells for flip angles less than α=25°. Theoretical and experimental results indicate that positive visibility (VIS_POS) was maximized at α=10° and 15°. Low flip angle SSFP also provided negative contrast comparable to standard SSFP and GRE imaging. Results suggest that USPIO-labeled macrophages are capable of producing the conditions necessary for positive contrast with FLAPS at clinical field strength (1.5 T) and resolution (0.8×0.8×3 mm³).     

Epitaxial growth of highly transparent and conducting Sc-doped ZnO films on c-plane sapphire by sol–gel process without buffer

Highly transparent and conductive scandium doped zinc oxide (ZnO:Sc) films were deposited on c-plane sapphire substrates by sol–gel technique using zinc acetate dihydrate [Zn(CH₃COO)₂·2H₂O] as precursor, 2-methoxyethanol as solvent and monoethanolamine as a stabilizer. The doping with scandium is achieved by adding 0.5 wt% of scandium nitrate hexahydrate [(ScNO₃·6H₂O)] in the solution. The influence of annealing temperature (300–550 °C) on the structural, optical and electrical properties was investigated. X-ray Diffraction study revealed that highly c-axis oriented films with full-width half maximum of 0.16° are obtained at an annealing temperature of 400 °C. The surface morphology of the films was judged by SEM and AFM images which indicated formation of grains. The average transmittance was found to be above 92% in the visible region. ZnO:Sc film, annealed at 400 °C exhibited minimum resistivity of 1.91 × 10⁻⁴ Ω cm. Room-temperature photoluminescence measurements of the ZnO:Sc films annealed at 400 °C showed ultraviolet peak at 3.31eV with a FWHM of 11.2 meV, which are comparable to those found in high-quality ZnO films. Reflection high-energy electron diffraction pattern confirmed the epitaxial nature of the films even without introducing any buffer layer.     

Palaeodose underestimates caused by extended-duration preheats in the optical dating of quartz

An optical dating study of some quartzose sediments from northern and southern Australia, north Africa and north-western Europe has revealed that palaeodose (P) underestimates of 10–40% are obtained when an extended-duration preheat of 160°C for 16 h is used. For these samples in the 0–60 ka age range, a preheat of 220°C for 5 min produces the correct P, as inferred from the concordance with thermoluminescence (TL) palaeodose determinations on the same sedimentary sample or on burnt flint. Independent support for use of the 220°C preheat is given by the agreement between optical ages younger than 30 ka and ¹⁴C age determinations on associated charcoal. The deleterious effect of the 160°C preheat is illustrated by growth curves of optically stimulated luminescence (OSL) vs added dose. These curves show that the 160°C preheat induces a dose-dependent increase in sample sensitivity, which may be related to activation of the pre-dose mechanism. The 160°C preheat also causes low-dose supralinearity, although the supralinearity correction is insufficient to reduce significantly the degree of P underestimation. A normalization method based on preheat-induced sensitivity changes of the 110°C TL peak, albeit limited by saturation effects, warrants further investigation.     

In vivo NMR T2 relaxation of experimental brain tumors in the cat: A multiparameter tissue characterization

Experimental gliomas (F98) were inoculated in cat brain for the systematic study of their in vivo T₂ relaxation time behavior. With a CPMG multi-echo imaging sequence, a train of 16 echoes was evaluated to obtain the transverse relaxation time and the magnetization M(0) at time t = 0. The magnetization decay curves were analyzed for biexponentiality. All tissues showed monoexponential T₂, only that of the ventricular fluid and part of the vital tumor tissue were biexponential. Based on these NMR relaxation parameters the tissues were characterized, their correct assignment being assured by comparison with histological slices. T₂ of normal grey and white matter was 74 ± 6 and 72 ± 6 msec, respectively. These two tissue types were distinguished through M(0) which for white matter was only 0.88 of the intensity of grey matter in full agreement with water content, determined from tissue specimens. At the time of maximal tumor growth and edema spread a tissue differentiation was possible in NMR relaxation parameter images. Separation of the three tissue groups of normal tissue, tumor and edema was based on T₂ with T_2(normal) < T_2(tumor) < T_2(edema). Using M(0) as a second parameter the differentiation was supported, in particular between white matter and tumor or edema. Animals were studied at 1–4 wk after tumor implantation to study tumor development. The magnetization M(0) of both tumor and peritumoral edema went through a maximum between the second and third week of tumor growth. T₂ of edema was maximal at the same time with 133 ± 4 msec, while the relaxation time of tumor continued to increase during the whole growth period, reaching values of 114 ± 12 msec at the fourth week. Thus, a complete characterization of pathological tissues with NMR relaxometry must include a detailed study of the developmental changes of these tissues to assure correct experimental conditions for the goal of optimal contrast between normal and pathological regions in the NMR images.