The quadrupole resonance properties of nondetonable explosive formulations for land mine detection machine calibration and testing

Explosive detection machines on the basis of quadrupole resonance (QR) technology are under development for land mine detection and other antiterrorism applications. The QR machines are optimized to detect the actual explosive ingredient in a detonable formulation and to ignore signals from other, benign materials. This presents a safety and logistical challenge for QR land mine detector testing and calibration because of the hazards involved when handling even small amounts of a detonable explosive. The detonation hazard can be mitigated by adding inert materials (desensitizers) to coat the crystalline explosive. The effect on the QR signal of various types of inert material is examined, with a view to developing a safe QR land mine target.     

Comparison of simulations and data from a seismo-acoustic tank experiment

A tank experiment was carried out to investigate underwater sound propagation over an elastic bottom in flat and sloping configurations. The purpose of the experiment was to evaluate range-dependent propagation models with high-quality experimental data. The sea floor was modeled as an elastic medium by a polyvinyl chloride slab. The relatively high rigidity of the slab requires accounting for shear waves in this environment. Acoustic measurements were obtained along virtual arrays in the water column using a robotic apparatus. Elastic parabolic equation solutions are in excellent agreement with data.     

The noise immunity of gradiometer coils for14N NQR land mine detection: Practical limitations

Magnetic resonance measurements in the field, such as for land mine detection using¹⁴N nuclear quadrupole resonance (NQR), must deal with large levels of environmental radio-frequency interference. One approach to minimize the level of interference which enters the NQR receiver is the use of a coil with no magnetic dipole moment. Such a coil is, ideally, sensitive only to spatial gradients of the magnetic fields and is referred to as a gradiometer. It is straightforward to estimate the amount of reduction one can expect for an ideal gradiometer. Here it is shown that for¹⁴N NQR land mine detection in practice, the ultimate level of interference received can be expected to be significantly greater than what one would expect solely due to these spatial gradients. This is due to the fact that it is quite difficult to construct an ideal gradiometer.     

Multi-wavelength laser sensor for intruder detection and discrimination

An intruder detection and discrimination sensor with improved optical design is developed using lasers of different wavelengths to demonstrate the concept of discrimination over a distance of 6 m. A distinctive feature of optics is used to provide additional transverse laser beam scanning. The sample objects used to demonstrate the concept of discrimination over a distance of 6 m are leaf, bark, black fabric, PVC, wood and camouflage material. A camouflage material is chosen to illustrate the discrimination capability of the sensor. The sensor utilizes a five-wavelength laser combination module, which sequentially emits identically-polarized laser light beams along one optical path. A cylindrical quasi-optical cavity with improved optical design generates multiple laser light beams for each laser. The intensities of the reflected light beams from the different spots are detected using a high speed area scan image sensor. Object discrimination and detection is based on analyzing the Gaussian profile of reflected light at the different wavelengths. The discrimination between selected objects is accomplished by calculating four different slopes from the objects' reflectance spectra at the wavelengths 473 nm, 532 nm, 635 nm, 670 nm and 785 nm. Furthermore, the camouflage material, which has complex patterns within a single sample, is also detected and discriminated over a 6 m range by scanning the laser beam spots along the transverse direction.     

Intensity discrimination and increment detection in cochlear-implant users

Intensity difference limens (DLs) were measured in users of the Nucleus 22 and Clarion v1.2 cochlear implants and in normal-hearing listeners to better understand mechanisms of intensity discrimination in electric and acoustic hearing and to evaluate the possible role of neural adaptation. Intensity DLs were measured for three modes of presentation: gated (intensity increments gated synchronously with the pedestal), fringe (intensity increments delayed 250 or 650 ms relative to the onset of the pedestal), and continuous (intensity increments occur in the presence of a pedestal that is played throughout the experimental run). Stimuli for cochlear-implant listeners were trains of biphasic pulses; stimuli for normal-hearing listeners were a 1-kHz tone and a wideband noise. Clarion cochlear-implant listeners showed level-dependent effects of presentation mode. At low pedestal levels, gated thresholds were generally similar to thresholds obtained in the fringe and continuous conditions. At higher pedestal levels, however, the fringe and continuous conditions produced smaller intensity DLs than the gated condition, similar to the gated-continuous difference in intensity DLs observed in acoustic hearing. Nucleus cochlear-implant listeners did not show consistent threshold differences for the gated and fringe conditions, and were not tested in the continuous condition. It is not clear why a difference between gated and fringe thresholds occurred for the Clarion but not the Nucleus subjects. Normal-hearing listeners showed improved thresholds for the continuous condition relative to the gated condition, but the effect was larger for the 1-kHz tonal carrier than for the noise carrier. Findings suggest that adaptation occurring central to the inner hair cell synapse mediates the gated-continuous difference observed in Clarion cochlear-implant listeners and may also contribute to the gated-continuous difference in acoustic hearing.     

Masking effects in binaural detection and interaural time discrimination

This study was designed to investigate the effects of masker level and frequency on binaural detection and interaural time discrimination. Detection and interaural time discrimination of a 700-Hz sinusoidal signal were measured as a function of the center frequency and level of a narrow-band masking noise. The masker was a continuous, diotic, 80-Hz-wide noise that varied in center frequency from 250 to 1370 Hz. In the detection experiment, the signal was presented either diotically (NoSo) or interaurally phase reversed (NoS pi). In the interaural time discrimination experiment, the signal level needed to discriminate a 30-microseconds interaural delay was measured. As would be expected, the presence of the masker has a greater effect on NoSo detection than NoS pi detection, and for masker frequencies at or near the signal frequency. In contrast, interaural time discrimination can be improved by the presence of a low-level masker. Also, performance improves more rapidly as the signal/masker frequency separation increases for NoSo detection than for interaural time discrimination and NoS pi detection. For all three tasks, significant upward spread of masking occurs only at the highest masker level; at low masker levels, there is a tendency toward downward spread of masking.     

Modulation interference in detection and discrimination of amplitude modulation

Two experiments were conducted to assess the effect of the rate of sinusoidal amplitude modulation (SAM) of a masker tone on detection of SAM of a probe tone (experiment 1) or on SAM-rate discrimination for the probe tone (experiment 2). When modulated at the same rate as the probe, the masker interfered with both the detection of probe modulation and the discrimination of the rate of probe modulation. The interference was obtained when the masker was either higher or lower in frequency than the probe (the probe and masker were separated by 2 oct). The amount of interference in detecting probe modulation (experiment 1) decreased as the common base rate of modulation was increased from 5 to 200 Hz. For rate discrimination (experiment 2), the amount of interference remained approximately the same for base rates of 2-40 Hz, the range over which rate discrimination was measured. In both experiments, the amount of interference was reduced when the masker was modulated at a different rate than the probe.     

Intensity discrimination and detection of amplitude modulation in electric hearing

Wojtczak and Viemeister [J. Acoust. Soc. Am. 106, 1917-1924 (1999)] demonstrated a close relationship between intensity difference limens (DLs) and 4-Hz amplitude modulation (AM) detection thresholds in normal-hearing acoustic listeners. The present study demonstrates a similar relationship between intensity DLs and AM detection thresholds in cochlear-implant listeners, for gated stimuli. This suggests that acoustic and cochlear-implant listeners make use of a similar decision variable to perform intensity discrimination and modulation detection tasks. It can be shown that the absence of compression in electric hearing does not preclude this possibility.     

Nonlinear photothermal and photoacoustic processes for crack detection

We show that, using the thermal and mechanical nonlinearities of cracks, it is possible to produce nonlinear effects in the process of thermoelastic laser-generation of sound at the surface of a metallic sample. Two independent laser bursts centered on two different frequencies f₁ and f₂ are focused on the same spot, which can be close or distant form an artificial surface crack. By recording the acoustic response of the sample, frequency spectra obtained at different spot distances from the crack are compared. We observe that the frequency components resulting from the nonlinear process of frequency mixing (f₁+f₂, 2f₁, 2f₂, ...) are detectable for a generation on the crack but are absent out of the crack. Possible future improvements and other opportunities of crack imaging or non destructive testing methods based on these nonlinear processes are discussed.     

Nonlinear acoustic techniques for landmine detection

Measurements of the top surface vibration of a buried (inert) VS 2.2 anti-tank plastic landmine reveal significant resonances in the frequency range between 80 and 650 Hz. Resonances from measurements of the normal component of the acoustically induced soil surface particle velocity (due to sufficient acoustic-to-seismic coupling) have been used in detection schemes. Since the interface between the top plate and the soil responds nonlinearly to pressure fluctuations, characteristics of landmines, the soil, and the interface are rich in nonlinear physics and allow for a method of buried landmine detection not previously exploited. Tuning curve experiments (revealing "softening" and a back-bone curve linear in particle velocity amplitude versus frequency) help characterize the nonlinear resonant behavior of the soil-landmine oscillator. The results appear to exhibit the characteristics of nonlinear mesoscopic elastic behavior, which is explored. When two primary waves f1 and f2 drive the soil over the mine near resonance, a rich spectrum of nonlinearly generated tones is measured with a geophone on the surface over the buried landmine in agreement with Donskoy [SPIE Proc. 3392, 221-217 (1998); 3710, 239-246 (1999)]. In profiling, particular nonlinear tonals can improve the contrast ratio compared to using either primary tone in the spectrum.     

Nondestructive discrimination of Greenberger-Horne-Zeilinger-basis states via two-qubit parity detection

We propose new methods to construct universal Greenberger-Horne-Zeilinger (GHZ)-state analyzers without destroying the qubits by using two-qubit parity gates. The idea can be applied to any physical systems where the two-qubit parity gate can be realized. We also investigate the feasibility of nondestructively distinguishing the GHZ-basis states for photonic qubits with such an idea. The nondestructive GHZ-state analyzers can act as generators of GHZ entangled states and are expected to find useful applications for resource-saving quantum information processing.     

鉴别野草和农作物的特异光电子引擎

文章作者在植物光谱识别的基础上提出了一种能够识别不同绿色植物的新颖光电子技术.该项技术运用于可见至近红外波段,在实验室环境和农田环境下,可以成功地采集和分析目标的光谱数据,对不同品种的绿色植物实施了精确识别.该项研究是由跨学科的西澳大利亚微光电子系统中心有限公司(the Western Australian Centre ofExcellence for MicroPhotonic Systems,Pty Ltd,)和中国大恒集团公司共同研究完成的,其目标是开发国际上首台野草传感器,使得除草剂的使用定位精确,既可显著提高作物的产量,又可节约80%除草剂,更重要的是保护环境,节约用水,对于农业和生态都有重要意义.     

Tone detection and synthetic speech discrimination in band-reject noise by hearing-impaired listeners

Frequency resolution was evaluated for two normal-hearing and seven hearing-impaired subjects with moderate, flat sensorineural hearing loss by measuring percent correct detection of a 2000-Hz tone as the width of a notch in band-reject noise increased. The level of the tone was fixed for each subject at a criterion performance level in broadband noise. Discrimination of synthetic speech syllables that differed in spectral content in the 2000-Hz region was evaluated as a function of the notch width in the same band-reject noise. Recognition of natural speech consonant/vowel syllables in quiet was also tested; results were analyzed for percent correct performance and relative information transmitted for voicing and place features. In the hearing-impaired subjects, frequency resolution at 2000 Hz was significantly correlated with the discrimination of synthetic speech information in the 2000-Hz region and was not related to the recognition of natural speech nonsense syllables unless (a) the speech stimuli contained the vowel /i/ rather than /a/, and (b) the score reflected information transmitted for place of articulation rather than percent correct.     

A signal detection analysis of auditory-frequency discrimination in the rat

The frequency-discrimination behavior of rats in a simple go/no-go task was analyzed using the theory of signal detection. Discrimination acuity was studied and the receiver operating characteristic (ROC) was generated in subjects by varying the reinforcement schedule and signal probability. The detectability indices d', A', and sensitivity index (SI) and response-bias indices B" and responsivity index (RI) were used to describe behavior. A' gave the most suitable psychometric functions while RI best described response-bias behavior. Weber ratios were 6.25% +/- 0.23% at 5 kHz in three subjects. The best method to obtain the ROC was to vary the probability with which subjects were reinforced. The ROC in two subjects demonstrated classical forms; in another subject, the function was asymmetric to the extent that detectability was not independent of response bias. Subjects altered their decision criterion in reporting a signal from trial to trial depending on previous trial events. On any given trial, subjects made a decision in one of several "decision states." Variables that influenced decision states included previous reinforcement and timeouts. The data indicate that timeouts may not be a useful feature in go/no-go tasks. The identification of multiple-decision states within a single behavioral session is a convenient method to generate the ROC without expressly manipulating experimental conditions.     

Three-dimensional parabolic equation model for seismo-acoustic propagation: Theoretical development and preliminary numerical implementation

A three-dimensional(3D) parabolic equation(PE) model for sound propagation in a seismo-acoustic waveguide is developed in Cartesian coordinates, with x, y, and z representing the marching direction, the longitudinal direction, and the depth direction, respectively. Two sets of 3D PEs for horizontally homogenous media are derived by rewriting the 3D elastic motion equations and simultaneously choosing proper dependent variables. The numerical scheme is for now restricted to the y-independent bathymetry. Accuracy of the numerical scheme is validated, and its azimuthal limitation is analyzed. In addition, effects of horizontal refraction in a wedge-shaped waveguide and another waveguide with a polyline bottom are illustrated. Great efforts should be made in future to provide this model with the ability to handle arbitrarily irregular fluid-elastic interfaces.     

Intensity discrimination, increment detection, and magnitude estimation for 1-kHz tones

Intensity difference limens (DLs) were measured over a wide intensity range for 200-ms, 1-kHz gated tones and for 200-ms increments in continuous 1-kHz tones. Magnitude estimates also were obtained for the gated tones over a comparable intensity range. The discrimination data are in general agreement with those from earlier studies but they extend them by showing: (1) good discrimination for gated tones over at least a 115-dB dynamic range; (2) a slight increase in the relative DL (delta I/I) as intensity increases above 95 dB SPL; (3) smaller DLs for increments than for gated tones, with the difference approximately independent of intensity; (4) negligible "negative masking" when thresholds are expressed as intensity differences (delta I). For two of the three subjects, magnitude estimates do not conform to a single-exponent power law for suprathreshold intensities. Over the middle range of intensities where a single exponent is appropriate, the value of the exponent is less than 0.1 for all subjects.     

Nonlinear ultrasonic wave modulation for online fatigue crack detection

This study presents a fatigue crack detection technique using nonlinear ultrasonic wave modulation. Ultrasonic waves at two distinctive driving frequencies are generated and corresponding ultrasonic responses are measured using permanently installed lead zirconate titanate (PZT) transducers with a potential for continuous monitoring. Here, the input signal at the lower driving frequency is often referred to as a ‘pumping’ signal, and the higher frequency input is referred to as a ‘probing’ signal. The presence of a system nonlinearity, such as a crack formation, can provide a mechanism for nonlinear wave modulation, and create spectral sidebands around the frequency of the probing signal. A signal processing technique combining linear response subtraction (LRS) and synchronous demodulation (SD) is developed specifically to extract the crack-induced spectral sidebands. The proposed crack detection method is successfully applied to identify actual fatigue cracks grown in metallic plate and complex fitting-lug specimens. Finally, the effect of pumping and probing frequencies on the amplitude of the first spectral sideband is investigated using the first sideband spectrogram (FSS) obtained by sweeping both pumping and probing signals over specified frequency ranges.