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41.
Small amplitude vibrations of an elastic structure completely filled by a fluid are considered. Describing the structure by displacements and the fluid by its pressure field one arrives at a non-selfadjoint eigenvalue problem. Taking advantage of a Rayleigh functional we prove that its eigenvalues can be characterized by variational principles of Rayleigh, minmax and maxmin type. 相似文献
42.
Jeramy Dickerson Konstantinos Pantzas Tarik Moudakir Abdallah Ougazzaden Paul L. Voss 《Optical and Quantum Electronics》2013,45(7):681-686
We report the numerical study of n-GaN/i-InGaN/p-GaN solar cells on Ga-face substrates with thin GaN interlayers present in the intrinsic InGaN region. These interlayers have recently been shown to significantly increase the crystal quality of thick InGaN layers $(>\!\!\!120\,\text{ nm})$ . We find that tunneling is efficient in n-i-p structures having interlayers $\le \! 1.5\,\text{ nm}$ thick if polarization charges are sufficiently screened. If left unscreened, the large polarization charges naturally formed at the heterointerfaces degrades n-i-p performance, at a given interlayer thickness, because polarization charges increase the distance that carriers must tunnel. Simulations identify favorable parameter ranges. 相似文献
43.
Heinz-Jürgen Voss 《Journal of Combinatorial Theory, Series B》1982,32(3):264-285
All 2-connected non-bipartite graphs are characterized which have a minimal valency ≥3 and which have no odd circuit with two or more chords. From this it is derived that in each graph with chromatic number ≥4 containing no complete 4-graph there is an odd circuit with two or more chords. This result was conjectured by P. Erdös. Corresponding results for even circuits and for circuits with a fixed edge are obtained. Some related problems of the Turán type are solved. 相似文献
44.
Balakin V Alexandrov VA Mikhailichenko A Flöttmann K Peters F Voss G Bharadwaj V Halling M Holt JA Buon J Jeanjean J LeDiberder F Lepeltier V Puzo P Heimlinger G Settles R Stierlin U Hayano H Ishihara N Nakayama H Oide K Shintake T Takeuchi Y Yamamoto N Bulos F Burke D Field R Hartman S Helm R Irwin J Iverson R Rokni S Roy G Spence W Tenenbaum P Wagner SR Walz D Williams S 《Physical review letters》1995,74(13):2479-2482
45.
46.
B. Buchholz H. -D. Kronfeldt G. Müller M. Voss R. Winkler 《Zeitschrift für Physik A Hadrons and Nuclei》1978,288(3):247-256
Optical hyperfinestructure investigations in several spectral lines were carried out in the Sb-I spectrum from which for the first time accurate values of the hfs-splitting constantsA andB of the ground configuration 5p 3 and also for five of the eight levels of the first excited configuration 5p 26s were obtained. With these parameters the influence of core polarization effects is calculated to bea c= ?6.6(4) mK, (equivalent to a magnetic field of ?283(20) kG perp-electron spin). The quadrupole momentQ 121= ?0.36(4) b (including Sternheimer correction) was obtained with the experimental valuesb 3/2= ?14.3(1.0) mK and 〈r ?3〉 =11.2(3) a.u. andQ 123= ?0.49(5) b withb 3/2= ?19.9(1.0) mK resp. This evaluation also yields the relativistic correction factor η= ?(C″/C′) · S r/R′ r=1.13(2). —For the first time, too, isotope shift investigations in Sb-I lines were possible which permit to determine the isotope shift constant βC exp= 40(10) mK, and a value δ〈r 2〉121, 123=0.12(4) fm2 for the change in the mean square nuclear charge radius between121Sb and123Sb which is about 50 percent of the prediction of the unified nuclear model. 相似文献
47.
Cytochrome p450(BioI)(CYP107H1) is believed to supply pimelic acid equivalents for biotin biosynthesis in Bacillus subtilis: we report here that the mechanistic pathway adopted by this multifunctional p450 for the in-chain cleavage of fatty acids is via consecutive formation of alcohol and threo-diol intermediates, with the likely absolute configuration of the intermediates also reported. 相似文献
48.
Let P
k be a path on k vertices. In an earlier paper we have proved that each polyhedral map G on any compact 2-manifold
with Euler characteristic
contains a path P
k such that each vertex of this path has, in G, degree
. Moreover, this bound is attained for k = 1 or k 2, k even. In this paper we prove that for each odd
, this bound is the best possible on infinitely many compact 2-manifolds, but on infinitely many other compact 2-manifolds the upper bound can be lowered to
. 相似文献
49.
Hyperoxaluria is the most important risk factor for a formation of calcium oxalate-urinary stones. Usually, the bulk of oxalate will be formed in the human body, but in many patients the oxalate from food plays the decisive role. Conventionally, in urine the endogenous oxalate can not be distinguished from food derived oxalate. We have developed a standardized oxalate-absorption test, applying a physiological dose (50 mg disodium salt of [13C2]oxalic acid) of labelled oxalate. The assay has been published. Now we report on the first extensive applications of this test in 86 volunteers and 135 patients from different groups with calcium oxalate stones or an increased risk of the formation of such stones. In one-third of the patients with calcium oxalate-urinary stones an oxalate hyperabsorption was diagnosed. For these patients, a dietetic stone prophylaxis and/or therapy is indicated. 相似文献
50.
Wessel N Ziehmann C Kurths J Meyerfeldt U Schirdewan A Voss A 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(1):733-739
Ventricular tachycardia or fibrillation (VT-VF) as fatal cardiac arrhythmias are the main factors triggering sudden cardiac death. The objective of this study is to find early signs of sustained VT-VF in patients with an implanted cardioverter-defibrillator (ICD). These devices are able to safeguard patients by returning their hearts to a normal rhythm via strong defibrillatory shocks; additionally, they store the 1000 beat-to-beat intervals immediately before the onset of a life-threatening arrhythmia. We study these 1000 beat-to-beat intervals of 17 chronic heart failure ICD patients before the onset of a life-threatening arrhythmia and at a control time, i.e., without a VT-VF event. To characterize these rather short data sets, we calculate heart rate variability parameters from the time and frequency domain, from symbolic dynamics as well as the finite-time growth rates. We find that neither the time nor the frequency domain parameters show significant differences between the VT-VF and the control time series. However, two parameters from symbolic dynamics as well as the finite-time growth rates discriminate significantly both groups. These findings could be of importance in algorithms for next generation ICD's to improve the diagnostics and therapy of VT-VF. 相似文献