Quantitative measurement of temperature by proton resonance frequency shift at low field: a general method to correct non-linear spatial and temporal phase deformations

MRI thermometry methods are usually based on the temperature dependence of the proton resonance frequency. Unfortunately, these methods are very sensitive to the phase drift induced by the instability of the scanner which prevents any temperature mapping over long periods of time. A general method based on 3D spatial modelling of the phase drift as a function of time is presented. The MRI temperature measurements were validated on gel samples with uniform and constant temperature and with a linear temperature gradient. In the case of uniform temperature conditions, correction of the phase drift proved to be essential when long periods of acquisition were required, as bias could reach values of up to 200 degrees C in its absence. The temperature uncertainty measured by MRI was 1.2 degrees C in average over 290 min. This accuracy is coherent with the requirements for food applications especially when thermocouples are useless.     

Nonlinear photonic crystals as a source of entangled photons

Nonlinear photonic crystals can be used to provide phase matching for frequency conversion in optically isotropic materials. The phase-matching mechanism proposed here is a combination of form birefringence and phase velocity dispersion in a periodic structure. Since the phase matching relies on the geometry of the photonic crystal, it becomes possible to use highly nonlinear materials. This is illustrated considering a one-dimensional periodic Al0.4Ga0.6As/air structure for the generation of 1.5 microm light. We show that phase-matching conditions used in schemes to create entangled photon pairs can be achieved in photonic crystals.     

Optimal quantum cloning on a beam splitter

We demonstrate how a beam splitter in combination with different light sources can be used as an optimal universal 1-->2 quantum cloner and as an optimal universal quantum NOT machine for the polarization qubit of a single photon. For the cloning a source of single photons with maximally mixed polarization is required and for the NOT operation a source of maximally entangled photon pairs. We demonstrate both operations with near optimal fidelity. Our scheme can be generalized in a natural way to clone and NOT the spin state of electrons.     

The materials science X‐ray beamline BL8 at the DELTA storage ring

The hard X‐ray beamline BL8 at the superconducting asymmetric wiggler at the 1.5 GeV Dortmund Electron Accelerator DELTA is described. This beamline is dedicated to X‐ray studies in the spectral range from ～1 keV to ～25 keV photon energy. The monochromator as well as the other optical components of the beamline are optimized accordingly. The endstation comprises a six‐axis diffractometer that is capable of carrying heavy loads related to non‐ambient sample environments such as, for example, ultrahigh‐vacuum systems, high‐pressure cells or liquid‐helium cryostats. X‐ray absorption spectra from several reference compounds illustrate the performance. Besides transmission measurements, fluorescence detection for dilute sample systems as well as surface‐sensitive reflection‐mode experiments have been performed. The results show that high‐quality EXAFS data can be obtained in the quick‐scanning EXAFS mode within a few seconds of acquisition time, enabling time‐resolved in situ experiments using standard beamline equipment that is permanently available. The performance of the new beamline, especially in terms of the photon flux and energy resolution, is competitive with other insertion‐device beamlines worldwide, and several sophisticated experiments including surface‐sensitive EXAFS experiments are feasible.     

ESPI solution for non-contacting MEMS-on-wafer testing

Rapid progress in the field of micro-electro-mechanical systems (MEMS) makes the development of appropriate measuring and testing means timely. Characterizing the mechanical properties of MEMS structures at a very early stage of manufacturing is a challenging task for quality assurance in this field. The paper describes a new solution that is based upon the vibration analysis of the microparts. The nanometer amplitudes are detected by advanced electronic speckle pattern interferometry (ESPI). A specific signal processing technique has been applied to make the solution robust. Comprehensive numerical simulations provide the theoretical base for the HNDT concept. A laboratory system for 4″ wafer has been built, and extensive tests show that such key properties as e.g. the thickness of springs or membranes can be determined exactly. Automated frequency scanning and corresponding digital image processing open the way to reliable and fast industrial systems for MEMS testing on wafer level.     

Chalcogenide Glass for Passive Infrared Applications

Chalcogenide glass fibers have been successfully used for remote spectroscopy, temperature sensing and CO2 laser power delivery. In bulk form, chalcogenide glass is the most promising candidate for replacing the expensive germanium lenses for thermal imaging.     

Effects of Professional Singing Education on Vocal Vibrato—A Longitudinal Study

Vocal vibrato is regarded as one of the essential characteristics of voice quality in classical singing. Professional singers seem to develop vibrato automatically, without actively striving to acquire it. In this longitudinal investigation, the vocal vibrato of 22 singing students was examined at the beginning of and after 3 years of professional singing education. Subjects sang an ascending-descending triad pattern in slow tempo on vowel [a:] at a comfortable pitch level twice at soft (piano) and twice at medium (mezzoforte) loudness. The top note of the triad pattern was sustained for approximately 5s. The mean and the standard deviation (SD) of the vibrato rate were measured for this note. Results revealed that after 3 years of training, voices with vibrato slower than 5.2 Hz were found to have a faster vibrato, and voices with vibrato faster than 5.8 Hz were found to have a slower vibrato. Standard deviation of vibrato rate was higher in soft than in medium loudness, particularly before the education. Also high values of SD of vibrato rate, exceeding 0.65 Hz, had decreased after the education. These findings confirm that vibrato characteristics can be affected by singing education.     

Air-coupled ultrasonic assessment of wood veneer

Air-coupled ultrasound (ACU) provides a tool to evaluate wood samples of small or moderate thickness (<30 mm) thereby avoiding direct contact or liquid coupling. Results of through-transmission ACU measurements on wood veneer samples and related products are reported with respect to a wide variety of quality aspects. Fluctuations in the averaged received signal levels appear to be correlated to the presence of natural or machine-induced thickness and density variations, flaws and grain damage, errors produced by the manufacturing process, insufficient bonding on a substrate, etc. In addition it is seen that the variability of the signal levels enables to distinguish between quarter and crown areas.     

Finite-Volume Fractional-Moment Criteria¶for Anderson Localization

A technically convenient signature of localization, exhibited by discrete operators with random potentials, is exponential decay of the fractional moments of the Green function within the appropriate energy ranges. Known implications include: spectral localization, absence of level repulsion, strong form of dynamical localization, and a related condition which plays a significant role in the quantization of the Hall conductance in two-dimensional Fermi gases. We present a family of finite-volume criteria which, under some mild restrictions on the distribution of the potential, cover the regime where the fractional moment decay condition holds. The constructive criteria permit to establish this condition at spectral band edges, provided there are sufficient “Lifshitz tail estimates” on the density of states. They are also used here to conclude that the fractional moment condition, and thus the other manifestations of localization, are valid throughout the regime covered by the “multiscale analysis”. In the converse direction, the analysis rules out fast power-law decay of the Green functions at mobility edges. Received: 21 October 1999 / Accepted: 31 March 2000 / Revised: 30 August 2001     

New excited superdeformed bands in heavy Pb nuclei: Clue for an octupole softness near the N = 118 gap at large deformation

We report the identification of six new superdeformed (SD) bands in ^197,198Pb observed with the EUROBALL IV spectrometer. The results are interpreted in the framework of cranked Hartree-Fock calculations with approximate projection on the particle number by means of the Lipkin-Nogami method. A mixing between quasi-particle excitations and an octupole vibration is suggested in the two SD isotopes. We have estimated the ordering of the neutron valence orbitals and confirm indirectly a N = 118 SD gap. Received: 20 December 2000 / Accepted: 24 January 2001