Rupture-disk-less shock-tube with compression tube driven by free piston

A new technique is proposed for a shock tube driven by a freely moving piston. In a conventional free-piston-driven shock tube, a rupture disk is employed between the compression tube and the shock generation tube. In the present method, however, the conventional rupture disk is replaced by a newly developed fast action valve which is activated by the compressed gas generated in the compression tube. The present method enables us to generate high Mach number shock waves of arbitrary strength with good reproducibility. The performance of the new method is demonstrated experimentally. This also enables us to be carefree to scattering of fragments of the rupture disk. Received 6 June 1996 / Accepted 6 October 1996     

A free-flight experiment of projectiles ranging from high subsonic to high supersonic Mach numbers

This paper reports a preliminary experiment with a free-flight range which was designed to be able to be driven by means of a sort of fast-acting valve. The notable characteristics pertinent to this type of range is the pliancy of operation and also the wide coverage of flight speed from the high subsonic to the high supersonic range. For both spherical and vehicle models, flight tests were conducted with shadowgraph observations and flight speed measurements in order to examine the capability of this type of facility.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Multiple sclerosis: Benefits of q-space imaging in evaluation of normal-appearing and periplaque white matter

Introduction

Diffusion tensor imaging (DTI) reveals white matter pathology in patients with multiple sclerosis (MS). A recent non-Gaussian diffusion imaging technique, q-space imaging (QSI), may provide several advantages over conventional MRI techniques in regard to in vivo evaluation of the disease process in patients with MS. The purpose of this study is to investigate the use of root mean square displacement (RMSD) derived from QSI data to characterize plaques, periplaque white matter (PWM), and normal-appearing white matter (NAWM) in patients with MS.

Methods

We generated apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps by using conventional DTI data from 21 MS patients; we generated RMSD maps by using QSI data from these patients. We used the Steel–Dwass test to compare the diffusion metrics of regions of interest in plaques, PWM, and NAWM.

Results

ADC differed (P < 0.05) between plaques and PWM and between plaques and NAWM. FA differed (P < 0.05) between plaques and NAWM. RMSD differed (P < 0.05) between plaques and PWM, plaques and NAWM, and PWM and NAWM.

Conclusion

RMSD values from QSI may reflect microstructural changes and white-matter damage in patients with MS with higher sensitivity than do conventional ADC and FA values.     

Novel cycloundecapeptides related to gramicidin S with both high antibiotic activity and low hemolytic activity

To find candidates with high antimicrobial and low hemolytic activities, many gramicidin S (GS) analogs of various ring sizes have been designed and synthesized. However, syntheses of antimicrobially active analogues of GS having a disordered symmetry structure from C(2) have almost never been reported, because the stable, amphiphilic β-sheet structure of GS with C(2) symmetry is considered essential for its strong antibacterial activity. In the present studies, novel thirteen cycloundecapeptides 1-13 related to GS were synthesized and examined. Among them, cyclo(-Va1(1)-Orn(2)-Leu(3)-D-Phe(4)-X(5)-Pro(6)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-) (X=Lys (10), Orn (11), Arg (12) and Lys(Lys) (13)) resulted in high antibiotic activity against both Gram-positive and Gram-negative microorganisms tested. In addition, 11 showed low toxicity against sheep blood cells compared with that of GS. Further, circular dichroism (CD) spectra of 10-13 had a curve similar to each other, suggesting that the conformations of these analogues in methanol are similar to each other. However, CD spectra of 10-13 were different from that of GS in the 190-210 nm region. These results suggest that the presences of one added amino acid residue at position 5 of 10-13 might be partially effective through a structural change in the biological activity of 10-13. In addition, the structural modifications at position 5 lower the undesirable hemolytic activity and enhance the desirable antibiotic activity.     

Practical Oxirane Ring Opening with In Situ Prepared LiCN; Synthesis of (2S,3R)-3-(2,4-Difluorophenyl)-3-hydroxy-2-methyl-4-(1H-1,2,4-triazol-1-yl)-1-butanenitrile

Trisubstituted oxirane 1 was regiospecifically opened with LiCN in situ prepared from acetone cyanohydrin and LiH to provide the corresponding β-hydroxy nitrile 2 in satisfactory yield, enabling us to manufacture a key intermediate for a new antifungal agent on a multi-kg scale. Some applications of this method to the ring opening of other oxiranes and nucleophilic substitution are also described.     

Extensive and subextensive chaos in globally coupled dynamical systems

Using a combination of analytical and numerical techniques, we show that chaos in globally coupled identical dynamical systems, whether dissipative or Hamiltonian, is both extensive and subextensive: their spectrum of Lyapunov exponents is asymptotically flat (thus extensive) at the value λ(0) given by a single unit forced by the mean field, but sandwiched between subextensive bands containing typically O(logN) exponents whose values vary as λ?λ(∞)+c/logN with λ(∞)≠λ(0).     

Correction for phase-shift deviation in a complex Fourier-transform integrated-optic spatial heterodyne spectrometer with an active phase-shift scheme

We report that a spectrum can be retrieved with a planar waveguide spatial heterodyne spectrometer (SHS) incorporating an active phase-shift scheme, where the phase shifts are distributed around π/2. This was confirmed experimentally with an SHS that had 32 interleaved Mach-Zehnder interferometers and whose free spectral range was 625 GHz. The phase shifts ranged from 0.71 to 2.2 rad against the target of π/2 rad.