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1

Digitale Medien

Characteristic modes of oscillatory chemical reactions (1990)

Sørensen, P. Graae ; Hynne, F. ; Nielsen, K.

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

The Journal of Chemical Physics 92 (1990), S. 4778-4785

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We show how eigenvectors of the Jacobi matrix @sJ and its transpose @sJT at a supercritical Hopf bifurcation can be used for quantitative characterization and analysis of models of oscillatory chemical reactions. Eigenvectors of @sJ determine the oscillations and the principal transients and can be expressed in terms of concentrations or reaction currents. Important reactions of a system can be easily identified this way. A pair of complex conjugate eigenvectors of @sJT associated with the bifurcation determines all independent quenchings of the oscillations. It can be used for quantitative comparison with experiment and in systematic search for better models. We combine the two sets of eigenvectors in a quantitative analysis of the effect of using a phase space of reduced dimension as an approximation to the full phase space. The analysis is illustrated by an explicit reduction of a five-dimensional Oregonator based model of the Belousov–Zhabotinskii reaction to a four-dimensional phase space involving a "quasi-species.'' The reduced phase space is tangent to a slow manifold at the bifurcating stationary point. Reconstruction of amplitudes and phases of the oscillations from incomplete quenching data is explained in terms of the reduced phase space.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.457695

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2

Digitale Medien

Quenching of chemical oscillations: General theory (1990)

Hynne, F. ; Sørensen, P. Graae ; Nielsen, K.

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

The Journal of Chemical Physics 92 (1990), S. 1747-1757

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We develop the theoretical basis for quenching analysis of small-amplitude chemical oscillations near a Hopf bifurcation in a concentration space of arbitrary dimension. (Quenching of a limit-cycle oscillation is carried out experimentally by instantaneously changing the concentrations of chemical species in a definite phase of the oscillation.) It is shown that quenching by addition of a species determines the reciprocal of the corresponding component of an eigenvector of the transposed Jacobi matrix. The set of all independent quenchings determines the tangent space of the stable manifold at the associated saddle focus even if only one species is monitored. Reconstruction of the oscillations from quenching data in an n-dimensional concentration space requires additional information if n〉3. We show that if n−2 chemical species are monitored the oscillatory parts of the remaining two (unknown) concentrations can be exactly calculated from the result of n quenchings. In this case one additional quenching by dilution suffices to determine also the two unknown average concentrations. Reconstruction from m quenchings with m−2 species monitored may still be possible with m less than the dimension; it will be exact if the species tested by quenching are the only ones oscillating, and an accurate approximation if the remaining n−m species oscillate with sufficiently small amplitudes. Experimental quenching data can be used for quantitative tests of models of an oscillatory system, and we show how quenching data can be calculated from models.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.458056

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3

Digitale Medien

Hopf bifurcation in chemical kinetics (1991)

Nielsen, K. ; Hynne, F. ; Sørensen, P. Graae

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

The Journal of Chemical Physics 94 (1991), S. 1020-1029

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: We study Hopf bifurcations in chemical reaction systems for their potential use in quantitative experimental analysis of the kinetics of oscillatory reactions. Three models of the Belousov–Zhabotinsky reaction are investigated as examples. For these we have determined and characterized the sub- and supercritical Hopf bifurcations in their dependence on parameters of the models. For supercritical bifurcations we calculate a number of parameters that can be used for quantitative comparison of models and experiment. In particular, we calculate expansion coefficients of the flow rate, the frequency of oscillation, and a Floquet exponent; the small parameter of the expansions is the square of the amplitude of the fundamental Fourier component of the oscillations. We also calculate quenching amplitudes from an adjoint eigenvector of the Jacobi matrix of the kinetics. They determine the conditions under which the small amplitude oscillations can be quenched by addition of the species participating in the reaction. The model properties are compared with experiment. They show qualitative, but not quantitative agreement.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.460057

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4

Digitale Medien

Prognostic factors and adjuvant treatment in early epithelial ovarian cancer (1993)

Bertelsen, K. ; Hølund, B. ; Andersen, J.E. ; [weitere]

238 Main Street, Cambridge, Massachusetts 02142, USA : Blackwell Scientific Publications

International journal of gynecological cancer 3 (1993), S. 0

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ISSN: 1525-1438

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Four hundred and ten patients with epithelial ovarian cancer FIGO stages I and II were registered by a Danish multicenter study group (The Danish Ovarian Cancer Group - DACOVA). Two-thirds were stage I, the most frequent substage was Iai which was the classification in 27%. Five-year survival for stage I was 72%, and 38% for stage II. Multivariate analysis showed that age, stage, residual tumor, histologic grade and adjuvant treatment had prognostic value. For stage, three significantly different groups could be identified: (1) stage Iai, (2) stage Iaii-Ic, and (3) stage II. Histologic grade showed a significant survival difference between all grades. Adjuvant treatment had a moderate but significant impact on survival. Patients in stage Iai had a good survival with surgery alone and will probably not benefit from adjuvant therapy. Adjuvant treatment improved survival for the remaining patients in stages I and II without residual tumor. A difference between treatment modalities was not observed. However, the data need to be confirmed by a randomized trial. Patients in stage II with residual tumor should be treated as stage III.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1525-1438.1993.03040211.x

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5

Digitale Medien

Laser conization for microinvasive carcinoma of the cervix. Short-term results (1993)

Andersen, E.S. ; Husth, M. ; Joergensen, A. ; [weitere]

238 Main Street, Cambridge, Massachusetts 02142, USA : Blackwell Scientific Publications

International journal of gynecological cancer 3 (1993), S. 0

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ISSN: 1525-1438

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Thirty-one patients with microinvasive carcinoma of the uterine cervix (less than 3.0 mm invasion, no lymph vascular involvement), were treated with combination laser conization. The mean follow-up period was 36 months. No cases of invasive disease have been diagnosed during follow-up. Examination during follow-up revealed atypical columnar epithelium in one case, but the hysterectomy specimen was normal. Based on these short-term results, combination laser conization for microinvasive carcinoma of the cervix seemed a sufficient therapy. A precise and careful histopathologic evaluation, and the patient acceptance of a strict follow-up schedule are mandatory to a decision to employ conservative management of microinvasive cervical carcinoma. Only long-term follow-up in patients treated by conservative therapy will be able to finally justify this approach.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1525-1438.1993.03030183.x

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6

Digitale Medien

Crystal structure and infrared and Raman spectra of potassium vanadyl sulfate (K4(VO)3(SO4)5) (1989)

Fehrmann, R. ; Boghosian, S. ; Papatheodorou, G. N. ; [weitere]

s.l. : American Chemical Society

Inorganic chemistry 28 (1989), S. 1847-1853

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ISSN: 1520-510X

Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/ic00309a018

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7

Digitale Medien

Spatial confinement and saturation of substitutional platinum by diffusion into ion-beam damaged silicon (1995)

Holm, B. ; Bonde Nielsen, K.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 78 (1995), S. 5970-5974

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The diffusion of platinum into lightly damaged regions of ion-implanted silicon has been investigated using deep-level transient spectroscopy and capacitance-voltage profiling. The samples consisted of PtSi/Si n-type Schottky diodes which had been implanted with O, F, or Cl to an intermediate depth between the zero-bias and reverse-bias depletion boundaries, and subsequently annealed at a temperature of 700 °C. The distribution of in-diffused Pt was obtained by monitoring the electron emission from the acceptor level (EC−ET=0.23 eV) previously assigned to Pt in a distorted substitutional configuration. The Pt was found to be distributed approximately congruous with the vacancy distribution generated during implantation. For a typical implantation dose (≈1011 cm−2) we recorded an enhanced accumulation of Pt by about two orders of magnitude as compared to diffusion into nonimplanted material. This apparent decoration of the primary damage profile occurs without the simultaneous introduction of other electrically active defects on a comparable scale. We infer that the residual damage present during annealing is sufficient to promote accumulation to saturation of substitutional Pt in the region of primary implantation damage. This rather remarkable property of guided in-diffusion, a kind of gettering phenomenon, may have potential applications in Si-device engineering. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.360600

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8

Digitale Medien

Significance of blackbody radiation in deep-level transient spectroscopy (1996)

Bonde Nielsen, K. ; Andersen, E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 9385-9387

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Deep-level transient spectroscopy has been combined with ion implantation in low-temperature investigations of deep centers in silicon. We demonstrate that thermal radiation, originating from vacuum chamber walls, can influence in situ recording of emission rates significantly. As an example, the emissivity (en) of the hydrogen E3′ center was found to be dominated by an optical contribution at temperatures below ≈65 K. A typical value, en(op)≈5.5 s−1, has been recorded in measurements with unshielded Au Schottky diodes. This effect of thermal radiation vanishes when a diode is fully encapsulated and thereby in thermal equilibrium with the radiation field. The optically induced emissivity is particularly large for the hydrogen center used here to illustrate the effect but has been observed for other deep centers as well. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.362571

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9

Digitale Medien

Nielsen, K. Bonde ; Holm, B.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 78 (1995), S. 5824-5826

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A process-induced metastable defect in n-type silicon is reported. The defect is found close to the wafer surface after combination of ambient gas-flow annealing at ≈900 °C depending on subsequent cleaning procedure. The defect gives rise to a band-gap level Ec−Et=0.25 eV observed by deep-level transient spectroscopy after reverse-bias cooling of the sample. Both annealing and generation of the defect proceed by 1st order processes. The activation enthalpies (ΔE) and pre-exponential factors (v) have been determined from Arrhenius analyses; the results are ΔE=0.63 eV and ν=1⋅1012 s−1 for annealing, and ΔE=0.65 eV and ν=6⋅1014 s−1 for generation. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.359647

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10

Digitale Medien

Formation of shallow donor in fluorine-implanted silicon (1996)

Holm, B. ; Nielsen, K. Bonde

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 1807-1809

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A shallow fluorine-related donor is reported. The donor has been revealed by capacitance–voltage profiling applied to furnace-annealed, fluorine-implanted silicon samples. The implantations were carried out at high energy, in the range 5–7 MeV. The assignment of the donor structure to fluorine results from a detailed examination of the effective space-charge distribution around the implantation range (≈4 μm) in comparison with data obtained for similar oxygen-implanted samples. The depth-integrated density of the donors formed after annealing at 700 °C is ≈3×1010 cm−2 corresponding to ≈1% of the implantation dose. The density increases by more than one order of magnitude for samples annealed only at 600 °C. In addition to the shallow donor level (or levels) a fluorine-specific level at Ec−Et≈0.15 eV has been assigned by application of deep-level transient spectroscopy. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.360973

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