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121.
Brightness waves of electroluminescent comets in ZnS:Cu single crystals have been investigated to decide whether the recombination occurs spontaneously or delayed by one half-period. Brightness waves during rising and decay, in addition to modifications of brightness waves due to disturbances of the stationary excitation by voltage pulses, exhibit delayed emission and a reservoir of excited centres exists in the stationary case. These results together with the time dependent blue-to-green ratio of the emission may be explained best on the basis of a bipolar field-emission model as proposed by Fischer. 相似文献
122.
In this paper, we give a probabilistic interpretation for a coupled system of Hamilton–Jacobi–Bellman equations using the
value function of a stochastic control problem. First we introduce this stochastic control problem. Then we prove that the
value function of this problem is deterministic and satisfies a (strong) dynamic programming principle. And finally, the value
function is shown to be the unique viscosity solution of the coupled system of Hamilton–Jacobi–Bellman equations. 相似文献
123.
Klaus Matthes Rainer Siegmund-Schultze Anton Wakolbinger 《Mathematische Nachrichten》1997,185(1):163-211
For time stationary Galton- Watson-branching populations on a general type space, the structure of the “individually positive recurrent part” of the system is described: its building blocks consist of finitely many “clans” with positive recurrent trunks. Conditions are given when this nubsystem is void, and when it equals the full system. In addition, positive recurrence on the clan level is characterized. Whereas individual positive recurrence turns out to be a symmetric concept with respect to forward and backward time direction (i. e., with respect to anceatral lines and offspring trees), with individual null recurrence this symmetry can fail even in the absence of branching, i.e., for independently migrating particle systems (Example 13.1). For discrete type spaces a classification of types as to the various individual recurrence concepts (positive, null, forward and backward in time) is proposed and illustrated by a couple of results and examples. For finite type spaces conditiom on the branching dynamics and its mean matrix for the existence of nontrivial equilibria are given. 相似文献
124.
Abazov VM Abbott B Abdesselam A Abolins M Abramov V Acharya BS Adams DL Adams M Ahmed SN Alexeev GD Alves GA Amos N Anderson EW Baarmand MM Babintsev VV Babukhadia L Bacon TC Baden A Baldin B Balm PW Banerjee S Barberis E Baringer P Barreto J Bartlett JF Bassler U Bauer D Bean A Begel M Belyaev A Beri SB Bernardi G Bertram I Besson A Beuselinck R Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Blazey G Blessing S Boehnlein A Bojko NI Borcherding F Bos K Brandt A Breedon R Briskin G Brock R 《Physical review letters》2001,87(6):061802
We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson. 相似文献
125.
Bertram Huppert 《Mathematische Zeitschrift》1957,68(1):126-150
Ohne Zusammenfassung 相似文献
126.
In the setting of vector-valued quantum fields obeying a linear wave-equation in a globally hyperbolic, stationary spacetime,
it is shown that the two-point functions of passive quantum states (mixtures of ground- or KMS-states) fulfill the microlocal
spectrum condition (which in the case of the canonically quantized scalar field is equivalent to saying that the two-pnt function
is of Hadamard form). The fields can be of bosonic or fermionic character. We also give an abstract version of this result
by showing that passive states of a topological *-dynamical system have an asymptotic pair correlation spectrum of a specific
type.
Received: 9 February 2000 / Accepted: 7 June 2000 相似文献
127.
Manz B 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,169(1):60-67
A fast method for quantitative imaging of T2 and displacement (flow and diffusion) is presented. The pulse sequence combines multi-PGSE NMR with multi-echo acquisition and compensates for flow effects in the read gradient and diffusion during multi-echo trains. The impact of the gradient pulses in a multi-echo train on the signal phase and amplitude is discussed. It is shown that separate T2 and displacement images with microscopic resolution can be obtained within minutes. The capability for 3D flow imaging is demonstrated. The sequence is then used to investigate forced detachment of a biofilm in a tube. 相似文献
128.
A pulse sequence producing a second stimulated echo is suggested for the compensation of relaxation and residual dipolar interaction effects in steady gradient spin echo diffusometry. Steady field gradients of considerable strength exist in the fringe field of NMR magnets, for instance. While the absolute echo time of the second stimulated echo is kept constant throughout the experiment, the interval between the first two radiofrequency pulses is augmented leading to a modulation of the amplitude of that second stimulated echo by self-diffusion only. The unique feature of this technique is that it is of a single-scan/single-echo-signal nature. That is, no reference signals neither of the same pulse sequence nor of separate experiments are needed. The new method was tested with poly(ethylene oxide) melts and proved to provide reliable data for (time dependent) self-diffusion coefficients down to the physical limit (D approximately 10(-15)m(2)/s) when flip-flop spin diffusion starts to become effective. 相似文献
129.
Schmidt M Voth E Schneider CA Theissen P Wagner R Baer FM Schicha H 《Magnetic resonance imaging》2004,22(2):229-236
Identification of akinetic but viable myocardium is important for the selection of patients for coronary revascularization. In order to assess predictive values of end-diastolic wall thickness and dobutamine induced wall thickening obtained by magnetic resonance imaging (MRI) and [18F]Fluorodeoxyglucose uptake assessed by positron emission tomography (F-18-FDG-PET), these parameters were compared to recovery of left ventricular function after successful revascularization. Forty patients with chronic myocardial infarction and regional a- or dyskinesia by ventriculography underwent rest- and dobutamine-MRI studies (10 microg dobutamine/kg body weight/min) and F-18-FDG-PET. Viability of the infarct region was considered to be present if; 1) end-diastolic wall thickness was > or =5.5 mm; 2) dobutamine induced wall thickening > or =2 mm could be measured; and 3) normalized F-18-FDG-uptake was > or =50% in > or =50% of akinetic segments. Preserved end-diastolic wall thickness was found in 32/40 patients, functional improvement during dobutamine infusion in 26/40 patients and preserved F-18-FDG-uptake in 29/40 patients. After revascularization regional left ventricular function improved in 25/40 patients. Positive and negative predictive values and diagnostic accuracy were 78%, 100%, and 83% for preserved end-diastolic wall thickness, 92%, 93%, and 93% for dobutamine inducible contraction reserve and 86%, 100%, and 90% for preserved F-18-FDG-uptake. Quantitative assessment of dobutamine induced systolic wall thickening by MRI and F-18-FDG-uptake by PET are highly accurate techniques for the identification of viable myocardium and prediction of functional recovery after successful revascularization. Preserved end-diastolic wall thickness results in an overestimation of viable myocardium compared to functional improvement, but wall thickness <5.5 mm excludes recovery of regional function. 相似文献
130.