Micromachined array tip for multifocus fiber-based optical coherence tomography

High-resolution optical coherence tomography demands a large detector bandwidth and a high numerical aperture for real-time imaging, which is difficult to achieve over a large imaging depth. To resolve these conflicting requirements we propose a novel multifocus fiber-based optical coherence tomography system with a micromachined array tip. We demonstrate the fabrication of a prototype four-channel tip that maintains a 9-14-microm spot diameter with more than 500 microm of imaging depth. Images of a resolution target and a human tooth were obtained with this tip by use of a four-channel cascaded Michelson fiber-optic interferometer, scanned simultaneously at 8 kHz with geometric power distribution across the four channels.     

Narrowband tuning of an injection-seeded pulsed optical parametric oscillator based on a self-adaptive, phase-conjugate cavity mirror

Narrowband tuning of a pulsed optical parametric oscillator (OPO) is achieved with a self-adaptive injection-seeded optical cavity employing a phase-conjugate reflector. This approach is used in a novel OPO system based on periodically poled KTiOPO4 and pumped at 532 nm by a pulsed Nd:YAG laser. The OPO is injection seeded at 835-855 nm by a continuous-wave tunable diode laser, which also enables a Rh:BaTiO3 photorefractive crystal to act as a wavelength-selective phase-conjugate reflector, with no need for active control of cavity length. The single-longitudinal-mode tunability and operational simplicity of this OPO system are demonstrated experimentally.     

Atomically resolved spin-dependent tunneling on the oxygen-terminated Fe3O4(111)

We employ spin-polarized STM to study the spin-dependent tunneling between a magnetite (111) sample and an antiferromagnetic tip through a vacuum barrier at room temperature. Atomic scale STM images show significant magnetic contrast corresponding to variations in the local surface states induced by oxygen vacancies. The estimated variations in tunneling magnetoresistance of 250% suggest that the spin-transport properties are significantly altered locally by the presence of surface defects.     

Peptide mimotopes of phomopsins: Identification, characterization and application in an immunoassay

Peptide mimotopes of plant-associated toxins offer the potential for improving analytical and diagnostic methodologies as well as providing candidates for potential protective vaccines against plant poisoning diseases. Monoclonal antibody (mAb) C₃C₁₁, which recognizes the antimicrotubule phomopsin mycotoxins, was used to isolate peptide mimics of phomopsin A from a random 15-mer phage display peptide library. A total of 46 clones were isolated that showed specific reactivity with the mAb. Amino acid sequence analysis revealed four different types of mimotope sequences, all of which contained a common motif V-A-L/V-C. Of the 46 clones isolated, 44 contained the motif V-A-L-C while 2 contained the V-A-V-C motif. All four types of phage clones inhibited the reactivity of the mAb with phomopsin A in a competition ELISA. The clone with the mimotope sequence CT VALCNMYFGAKLD demonstrated the strongest binding. It was further shown that synthetic peptides containing these mimotope amino acid sequences were able to inhibit the mAb-phomopsin A interaction, indicating that the peptide mimotopes were responsible for the specific binding, independent of the phage framework. The results also suggest that the mimotope peptides bind to mAb C₃C₁₁ at the same site as phomopsin A. The application of recombinant phage particles carrying phomopsin mimotopes in immunoassay was evaluated and the results demonstrated approximately 100-fold increase in sensitivity in comparison with a conventional immunoassay using a chemically linked phomopsin-horseradish peroxidase conjugate.     

Across-ear interference from parametrically degraded synthetic speech signals in a dichotic cocktail-party listening task

Recent results have shown that listeners attending to the quieter of two speech signals in one ear (the target ear) are highly susceptible to interference from normal or time-reversed speech signals presented in the unattended ear. However, speech-shaped noise signals have little impact on the segregation of speech in the opposite ear. This suggests that there is a fundamental difference between the across-ear interference effects of speech and nonspeech signals. In this experiment, the intelligibility and contralateral-ear masking characteristics of three synthetic speech signals with parametrically adjustable speech-like properties were examined: (1) a modulated noise-band (MNB) speech signal composed of fixed-frequency bands of envelope-modulated noise; (2) a modulated sine-band (MSB) speech signal composed of fixed-frequency amplitude-modulated sinewaves; and (3) a "sinewave speech" signal composed of sine waves tracking the first four formants of speech. In all three cases, a systematic decrease in performance in the two-talker target-ear listening task was found as the number of bands in the contralateral speech-like masker increased. These results suggest that speech-like fluctuations in the spectral envelope of a signal play an important role in determining the amount of across-ear interference that a signal will produce in a dichotic cocktail-party listening task.     

MRI findings of primary small-cell carcinoma of kidney

We report the MRI findings of primary small-cell carcinoma of the kidney (PSCCK) in a 59-year-old female. This tumor appeared as a 16-cm mass that arose from the right kidney. This lesion had diminished signal on T1-weighted images and heterogeneous mixed signal on T2-weighted images. The tumor primarily involved the renal medulla with persistent thin renal cortex. Despite the tumors' large size, no substantial central necrosis was present. The predominant medullary location and the lack of central necrosis in this large tumor were features unusual for renal cell carcinoma and should raise the suspicion of another malignancy, the differential diagnosis of which should contain extrapulmonary small-cell carcinoma of the kidney.     

Vibration analysis and measurement of a gradient coil insert in a 4 T MRI

High speed switching of current in gradient coils within high magnetic field strength Magnetic Resonance Imaging (MRI) scanners may result in high acoustic sound pressure levels in and around these machines. Many studies have already been conducted to characterize the sound field in and around MRIs and various methods have been investigated to attenuate the noise generated. To characterize the vibration properties of the gradient coil, a modified Finite Element (FE) model was developed according to the dimensional design of an available gradient coil insert and the concentration of the copper windings in the coil. The finite element analysis results were verified through experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Comparisons show that the FE model predicts the vibration properties extremely accurately. Based on the verified FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again verified through experimental vibration testing with the gradient coil insert installed in a 4 T MRI and excited using swept sinusoidal time waveforms. Through a comparison of the vibration signals generated it was found that the vibration resonances, both from the FE model and the experimental vibration testing, shift to higher frequencies after the boundary constraints were applied, as was expected. The predicted vibration response was very close to that measured from the gradient coil insert in operation. The FE modeling procedure that has been developed could easily be used to accurately predict the vibration properties of other gradient coil designs. Furthermore, the vibration analysis results from the FE model could be used in acoustic noise analysis to predict the sound pressure level produced by different types of input current pulse sequences.     

Phonon modes at the 2H-NbSe2 surface observed by grazing incidence inelastic x-ray scattering

We have determined the dispersion of acoustic and optical surface phonon modes 2H-NbSe2 at the by inelastic x-ray scattering under grazing incidence conditions. Already, at room temperature, an anomaly is observed close to the charge density wave -vector position located at about one-third along the Gamma-M direction of the Brillouin zone. Our results indicate that the anomaly for the surface mode occurs at a lower energy than that measured in bulk sensitive geometry in the same experiment, showing evidence of a modified behavior in the uppermost layers. We demonstrate that inelastic x-ray scattering in grazing incidence conditions provides a unique tool to selectively study either surface or bulk lattice dynamics in a single experiment.     

First ultraviolet high-gain harmonic-generation free-electron laser

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.     

Measurements of wave-breaking radiation from a laser-wakefield accelerator

Spectral analysis of radiation emitted transverse to laser propagation in laser-wakefield acceleration experiments shows broadband emission when electrons are accelerated to relativistic energies. The region over which emission occurs is short compared with the overall interaction length. The energy of the emission and location along the interaction length both vary with plasma density. A model for the radiation from self-trapped electrons indicates that the emission is a signature of the violent initial acceleration, and hence can be used as a diagnostic of the self-injection mechanism.