ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Dynamics of sodium ions in NaClO4 complexed in poly(propylene-oxide): A 23Na nuclear magnetic resonance study (1998)

Chung, S. H. ; Jeffrey, K. R. ; Stevens, J. R.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 108 (1998), S. 3360-3372

add to mindlist on the mindlist

Details

ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Amorphous poly(propylene oxide), PPO (molecular weights, 425 and ∼106), complexed with NaClO4 salt has ionic conductivities as high as 10−5 S/cm at room temperature. In an attempt to directly study the dynamics of the Na+ ions, (I=3/2) nuclear magnetic resonance (NMR) spin-lattice relaxation times, T1, and spin–spin relaxation times, T2, at a resonance frequency of 77.0 MHz have been measured over the temperature range from 150 to 390 K. A range of salt compositions [(PPO)nNaClO4; n=8–30] have been investigated. In addition, the glass transition temperature for each sample is reported. The recovery of equilibrium magnetization following a π/2 pulse is biexponential as expected for a spin I=3/2 system in the viscous liquid region. Below Tg a better fit to the magnetization recovery curve can be obtained if Kohlrausch–Williams–Watts (KWW) functions are used in place of the exponential functions. At low temperature the molecular motion has slowed to the point where a common spin temperature is not achieved by ionic diffusion. Two T2 values are observed over a limited temperature region near the T1 minimum. In the remaining low temperature region only the T2 associated with the central transition could be determined because the large 23Na quadrupole coupling constant made detection of the satellite transitions impossible. There is no evidence from the NMR relaxation time data for two Na+ populations. The experimental spin-lattice relaxation times can be analyzed to determine the correlation time for the ionic motion as a function of reciprocal temperature. The correlation time data display a distinct change in behavior at Tg which is interpreted as an indication of a crossover between two ionic transport mechanisms. Plots of T1 as a function of Tg/T indicate that dynamics for T〉Tg are largely determined by the flexibility of the polymer host (the α process) whereas a different process dominates for T〉Tg (presumably the β process). A comparison of correlation times derived from NMR relaxation times and ionic conductivities show a marked difference especially in the region of Tg. The conductivity decreases rapidly while the sodium ion motion continues with a correlation time ∼10−6 s through the glass transition. © 1998 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.475735

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

2

Electronic Resource

An electrophysiological study of the hippocampus of the ‘reeler’ mutant mouse (1974)

BLISS, T. V. P. ; CHUNG, S. H.

[s.l.] : Nature Publishing Group

Nature 252 (1974), S. 153-155

add to mindlist on the mindlist

Details

ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Here we report evidence which suggests that there is a high safety factor in the developmental processes responsible for ensuring orderly synaptic organisation. Despite the cellular disarray in the hippocampus of the homozygous reeler, the resultant synaptic organisation as revealed by ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/252153a0

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

3

Electronic Resource

An experiment on the breakup of impinging droplets on a hot surface (1996)

Ko, Y. S. ; Chung, S. H.

Springer

Experiments in fluids 21 (1996), S. 118-123

add to mindlist on the mindlist

Details

ISSN: 1432-1114

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract Breakup characteristics of liquid droplets impinging on a hot surface are investigated experimentally with the wall temperatures in the Leidenfrost temperature range of 220–330°C for n-decane fuel. Factors influencing droplet breakup are wall temperature, impinging velocity, droplet diameter and impinging angle. The 50% breakup probability shows that the impinging velocity decreases linearly with the droplet diameter increase and there exists an optimum impinging angle near 80° having the minimum value in the impinging velocity for given wall temperature and droplet size. Near the wall temperature of 250°C corresponding to the Leidenfrost temperature, a peculiar nonlinear behavior in the breakup probability is observed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00193915

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

4

Electronic Resource

Suggestive correctional methods for PIV image biasing caused by a rotating mirror system (1996)

Lee, S. D. ; Chung, S. H. ; Kihm, K. D.

Springer

Experiments in fluids 21 (1996), S. 201-208

add to mindlist on the mindlist

Details

ISSN: 1432-1114

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract A rotating mirror is widely used to generate the velocity shift that can resolve the directional ambiguities of PIV (particle image velocimetry) measurements. The rotating mirror system inevitably creates the normal displacement of the resulting PIV images and causes systematic image errors. Two corrective methods are proposed to eliminate or reduce the image biasing in PIV system. The use of two linearly traversing mirrors, instead of a single rotating mirror, shows that image biasing can be eliminated and the velocity shift well generated. As a second option, two co-rotating mirrors, instead of one, can reduce the image biasing with a maximum velocity shift available. Detailed imaging kinematics of the two suggestive methods are presented to lead to designing of practical devices that improve the PIV capabilities by reducing the systematic image errors.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00191692

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

5

Electronic Resource

Ionic conduction in composite polymer electrolytes at subambient temperatures (1996)

Wieczorek, W. ; Chung, S. H. ; Stevens, J. R.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2911-2917

add to mindlist on the mindlist

Details

ISSN: 0887-6266

Keywords: composite polymer electrolytes ; conduction mechanism ; glass transition temperature ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The majority of investigations carried out on polymer(SINGLEBOND) salt systems have been on polyether electrolytes at moderate temperatures where such electrolytes exhibit macroscopic uniformity. Relatively little attention has been paid to the subambient temperature region where composite electrolytes based on polyethers exhibit much higher conductivities than their pure polyether electrolyte analogues. For all of the composite systems studied the conduction mechanism changes from one in which the ions are coupled to the polymer segmental relaxations to one in which the ions are decoupled and thermally activated ionic hopping produces higher conductivities than would be expected from ion-segmental coupling and higher than observed for the base polyether(SINGLEBOND) salt system. This change has been observed at temperatures between 10 and 80°C above the respective glass transition temperatures. The relationship between this interaction and these higher conductivities at subambient temperatures is explored and discussed. © 1996 John Wiley & Sons, Inc.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

6

Electronic Resource

Optimal process design in non-isothermal, non-steady metal forming by the finite element method (1998)

Chung, S. H. ; Hwang, S. M.

Chichester [u.a.] : Wiley-Blackwell

International Journal for Numerical Methods in Engineering 42 (1998), S. 1343-1390

add to mindlist on the mindlist

Details

ISSN: 0029-5981

Keywords: optimal design ; design sensitivity ; direct differentiation method ; non-isothermal ; metal forming ; finite element method ; Engineering ; Numerical Methods and Modeling

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Mathematics , Technology

Notes: A new approach to process optimal design in non-isothermal, non-steady-state metal forming is presented. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical finite element process model so as to cover diverse objective functions and design variables, and a derivative-based approach is adopted for conducting optimization. The process model, the formulation for process optimal design, and the schemes for the evaluation of the design sensitivity, and an iterative procedure for optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach to deal with diverse process parameters and objective functions is demonstrated through applications to some selected process design problems. © 1998 John Wiley & Sons, Ltd.

Additional Material: 23 Ill.

Type of Medium: Electronic Resource

Permalink