Improved synthesis of polyfluorinated l-lysine for 19F NMR-based screening

Polyfluorinated N-α-Fmoc--Boc-l-lysine represents the best-in-class among a set of polyfluorinated amino acids (PFAs) which are useful tools for ¹⁹F NMR-Based Screening. In this communication, optimized reaction conditions that allowed for the multi-gram preparation of this unnatural amino acid are reported.     

Evaluation of ADC measurements among solid pancreatic masses by respiratory-triggered diffusion-weighted MR imaging with inversion-recovery fat-suppression technique at 3.0 T

Purpose

The objective of this paper was to investigate the value of apparent diffusion coefficients (ADCs) for differential diagnosis among solid pancreatic masses using respiratory triggered diffusion-weighted MR imaging with inversion-recovery fat-suppression technique (RT-IR-DWI) at 3.0 T.

Materials and Methods

20 normal volunteers and 72 patients (Pancreatic ductal adenocarcinoma [PDCA, n = 30], mass-forming pancreatitis [MFP, n = 15], solid pseudopapillary neoplasm [SPN, n = 12], and pancreatic neuroendocrine tumor[PNET, n = 15]) underwent RT-IR-DWI (b values: 0 and 600 s/mm²) at 3.0 T. Results were correlated with histopathologic data and follow-up imaging. ADC values among different types of pancreatic tissue were statistically analyzed and compared.

Results

Statistical difference was noticed in ADC values among normal pancreas, MFP, PDCA, SPN and PNET by ANOVA (p < .001). Normal pancreas had the highest ADC value, then followed by PNET, PDCA, MFP and SPN. There was noticeable statistical difference in ADC values among PDCA, MFP and normal pancreas by Least Significant Difference (LSD) (p < .001). ADC of SPN was statistically lower than that of PNET (p = 0.1800 × 10^− 4), PDCA (p = 0.0300 × 10^− 4) and normal pancreas (p = 0.0007 × 10^− 4). ADC of PNET was statistically lower than that of normal pancreas (p = 0.0360) and higher than that of MFP (p = 9.3000 × 10^− 4).

Conclusions

ADC measurements using RT-IR-DWI at 3.0 T may aid to disclose the histopathological pattern of normal pancreas and solid pancreatic masses, which may be helpful in characterizing solid pancreatic lesions.     

Correction of B0 susceptibility induced distortion in diffusion-weighted images using large-deformation diffeomorphic metric mapping

Geometric distortion caused by B0 inhomogeneity is one of the most important problems for diffusion-weighted images (DWI) using single-shot, echo planar imaging (SS-EPI). In this study, large-deformation, diffeomorphic metric mapping (LDDMM) algorithm has been tested for the correction of geometric distortion in diffusion tensor images (DTI). Based on data from nine normal subjects, the amount of distortion caused by B0 susceptibility in the 3-T magnet was characterized. The distortion quality was validated by manually placing landmarks in the target and DTI images before and after distortion correction. The distortion was found to be up to 15 mm in the population-averaged map and could be more than 20 mm in individual images. Both qualitative demonstration and quantitative statistical results suggest that the highly elastic geometric distortion caused by spatial inhomogeneity of the B0 field in DTI using SS-EPI can be effectively corrected by LDDMM. This postprocessing method is especially useful for correcting existent DTI data without phase maps.     

Processing of Spectropolarization Video Images

This paper considers the possibilities and results of using spectropolarization video photography of scenes for discriminating artificial and natural objects. A number of new methods for processing spectropolarization video images are proposed.     

Structural and electronic properties of gold nanowires

We have used high resolution transmission electron microscopy to determine the structure of gold nanowires generated by mechanical stretching. Just before rupture, the contacts adopt only three possible atomic configurations, whose occurrence probabilities and quantized conductance were subsequently estimated. These predictions have shown a remarkable agreement with conductance measurements from a break junction operating in ultra-high-vacuum, corroborating the derived correlation between nanowire atomic structure and conductance behavior. Received 28 November 2000     

Determination of the Gamow–Teller strength function for the neutron-deficient isotopes In

The Gamow–Teller β decays of the neutron-deficient indium isotopes ^104–107In have been investigated by using total absorption γ-ray spectrometry on mass-separated sources. The experimental Gamow–Teller strength, deduced as a function of the excitation energy in the daughter nuclei ^104–107Cd, is compared to shell-model predictions.     

Calculation of pulsed NMR signal in I = 3/2 quadrupolar spin system

The rf pulse response of I=3/2 spin system experiencing first order quadrupolar splitting is studied using density matrix approach. A general expression is derived in terms of spin populations, quadrupole splitting and duration and amplitude of the rf pulse for calculating the NMR signal arising due to the centre line and satellite resonances for the situation where the impressed rf pulse excites the resonances selectively as well as non-selectively. The necessary 4×4 transformation matrix obtained analytically by diagonalyzing the Hamiltonian are used to get the expression for the centre line response. The satellite signals are obtained in the same way but by using the numerical values of the roots of the related quartics. The widths of the corresponding π/2-pulses are calculated for different initial spin populations. The variations of this pulse-width and the corresponding signal amplitude as a function of satellite splitting are studied.     

On the efficiency of small-angle Čerenkov second harmonic generation in optical waveguides

It is well known that in the non-depleted pump approximation, the efficiency of a second harmonic generation (SHG) of a guided mode in a non-linear optical waveguide increases quadratically with the interaction length (P ₂ L ²), and linearly (P ₂ L) in the erenkov regime. The efficiency of the erenkov SHG in the waveguide with a non-linear substrate and linear guiding layer is known to be strongly peaked at a particular pump wavelength and a particular waveguide thickness, with the erenkov angle approaching zero. The known theory predicts an infinite efficiency value at the peak, however. In this contribution, a simple integral expression for the SHG efficiency in the erenkov regime is derived. For large erenkov angles and interaction lengths it yields the expected P ₂ L dependence, while in the limit of small erenkov angles the dependence is found to have the form of P L ^3/2, possessing also a finite value at the efficiency peak. The condition determining the accurate position of the efficiency peak in the waveguide thickness–pump wavelength plane is given, too.     

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.