Moderate Excitation Research Articles

Symbiotic Star as 201: a Planetary Nebula

AbstractOptical spectrum of AS 201 is presented: this object shows emission lines of moderate excitation (exc.class 5) and absorption spectrum of a G2III star. For the interstellar extinction and distance the values c=0.45 and d=1.5 kpc were estimated. The hot components of AS 2Ol, Cn 1–1 and M 1–2 are located on the Harman-Seaton sequence in the region of evolved central stars of PN. It is suggested that the hot components of some SS are evolved nuclei of PN; high el.density of their nebulae may be explained due to mass loss from the respective cool stars of the binaries.

Thermodynamics of strain-confined paraexcitons in Cu2O.

The thermodynamic behavior of long-lived paraexcitons confined to a parabolic potential well is examined. The potential well is produced by a Hertzian contact stress. A wavelength-tunable dye laser is used to create excitons directly in the potential well or at any other localized point inside the crystal. Spectral and spatial distributions of the exciton recombination luminescence are measured for cw and pulsed excitation. The possibility of Bose-Einstein condensation of these long-lived excitons is examined both theoretically and experimentally. We calculate the spectral and spatial distribution of luminescence from a gas of noninteracting particles in a three-dimensional harmonic-oscillator well. The results are markedly different for direct (no-phonon) and indirect (phonon-assisted) recombination. The calculated spectra are compared to the data for moderate cw excitation at ${T}_{\mathrm{bath}=2--}$4.2 K. Taken alone, the no-phonon spectra suggest that the excitonic gas is in the quantum regime; however, this conclusion is shown to be inconsistent with the estimated density of the gas. A consistent interpretation of all spectral and spatial distributions is possible, however, if one assumes Maxwell-Boltzmann statistics and takes into account the rapidly changing paraexciton intensity with applied stress. From time- and space-resolved studies of the orthoexciton and paraexciton luminescence, plausible causes for a saturation of paraexciton density in the strain well are deduced. First, an Auger-like recombination of colliding paraexcitons seems to limit their density---an idea supported by the observed power dependence of orthoexciton and paraexciton signals. Secondly, an anomalously slow thermalization of strain-confined paraexcitons is observed.

Photodissociation dynamics and potential surfaces of hydrogen peroxide

The dynamics of photodissociation of H2O2 from low lying excited electronic states was studied by classical trajectory calculations. Potential energy functions were constructed for both the ground and two excited states of H2O2. Parameters in the ground state function were chosen to fit vibrational frequencies, potential barriers, and the equilibrium structure. Parameters in the excited state functions were chosen to fit the observed OH rotational state distribution and to be consistent with the electronic spectrum. The moderate rotational excitation of the OH radicals is mostly explained by the fact that the repulsive O–O force exerts a small torque around the center of mass of the OH radicals. The results at 5.00 and 6.42 eV cannot both be fit with the same potential surface suggesting that at least two if not all three of the low lying excited states predicted by Evleth play a role in the electronic absorption. The importance sampling technique was used to weight the initial conditions with the Wigner distribution. As a consequence only a modest (103) number of trajectories were needed to generate a representative rotational distribution. One useful result which may be general is that the rotational distributions resulting from a given surface were little dependent on the photon energy but that use of a steeper potential gave rise to more rotational excitation.

Exciton-plasma Mott transition in CdSe at 77K

Photoluminescence spectra of CdSe obtained in conditions of moderate excitation densities show anomalies in the behavior of peak position and intensity. These anomalies, on the basis of the optical gain and in the shift of peak position to lower energy side, are ascribed to the onset of an exciton-plasma Mott-transition in the photoexcited semiconductor.

Level densities in mean-field theory versus the independent particle model

We point out that nuclear level densities at moderate excitation are systematically greater in mean-field theory than in the independent-particle model because self-consistency lowers the energies of excited states. We estimate the effect using a harmonic-oscillator model for 40Ca and find a 10% change in the level density parameter a, which is a disappointingly small effect. The main effect of self-consistent shapes is a substantial smearing of shell structure.

Laser-induced nonlinear absorption in silicon: Free-carrier absorption versus thermal effects

The optical-absorption coefficient of silicon has been determined under moderate ($\ensuremath{\lesssim}0.15$ J/${\mathrm{cm}}^{2}$) nanosecond laser excitation, between 2.0 and 2.6 eV. With respect to the cw low-power value, an enhancement under irradiation is observed on the whole range of fluence and wavelength. This enhancement builds up with the pump pulse and persists a long time after its end. It is shown that the features of the effect, i.e., dependences on time, fluence, and wavelength, can be interpreted by a thermally induced absorption enhancement. This mechanism is operative above 2.0 eV, whereas, under this value, the free-carrier absorption process is dominant.

Structure-taste relationship of glutamyl valine, the ‘sweet’ peptide for the fleshfly: The specific accessory site for the glutamyl moiety in the sugar receptor

l-Glutamyl- l-valine (Glu-Val) is one of the most stimulative dipeptides for the sugar receptor of the fleshfly. On the other hand, glutaryl- l-valine (Glt-Val) was almost ineffective. While N-acetylation of the α-amino group of the glutamyl (Glu) moiety in Glu-Val almost abolished responses, N-formylation of the group decreased the response appreciably but its effectiveness was clearly maintained. l-γ- O-Methyl-glutamyl- l-valine [Glu(γ- O Me)-Val] and l-glutaminyl- l-valine (Gln-Val) still gave moderate excitation, while l-glutamyl- l-valine methyl ester resulted in extremely decreased responses. Valeryl- l-valine, having neither the α-amino nor the γ-carboxyl group of the Glu moiety, was naturally ineffective in stimulating the sugar receptor. These results suggest the presence of a specific accessory site for the Glu moiety in Glu-Val located close to the aliphatic carboxylate (T) site in the sugar receptor.

Distribution of recombination lifetimes in amorphous silicon

Light-induced ESR (LESR) and luminescence in aSi:H are studied in order to resolve a recent controversy over whether the low temperature recombination is geminate or non-geminate. New transient measurements find that at moderate excitation intensities, luminescence is predominately monomolecular, whereas LESR is not. We show that the different behavior occurs because there is a very broad distribution of decay times for geminate electron-hole pairs. LESR is dominated by a small fraction of the pairs which have a very long decay time and which therefore slowly generate a non-geminate distribution. Luminescence is dominated by the closer geminate pairs that recombine quickly.

HOT ELECTRON EMISSION FROM SILICON UNDER PULSED LASER EXCITATION

Under moderate pulsed laser excitation, silicon is shown to emit electrons in the vacuum at photon energies well below the work function $. Two distinct processes are observed, 1) a two-quantum photoemission at low photon fluxes and high photon energies (> $/2) arid, 2) a thermoemission at high photon fluxes or low photon energies (< §/2). While the first effect yields information about the electronic structure of silicon under irradiation, the second one probes the properties of the carrier plasma. The temperature of this plasma has been evaluated to (1800 + 100) K for (0.04 Jem , 2 ns) irradiances.

Atomic iron transitions in the multiphoton ionization spectra of iron carbonyl and ferrocene near 300 nm

Atomic iron lines in the multiphoton ionization spectra (MPI) of ferrocene and iron carbonyl have been observed, showing that dissociation, preceding ionization, occurs under moderate laser excitation conditions.

Luminescence of highly excited ZnSe

Two-photon-resonant Raman scattering due to the excitonic molecule has been observed at LHeT, and its binding energy is found to be 2.2 meV for two triplet excitons. A luminescence band due to the excitonic molecule is confirmed under moderate power excitation (⪅50 kW/ cm 2) in very pure single crystals.

Compact emission regions and blue stellar objects in the northeast halo of NGC 5128

view Abstract Citations (45) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Compact emission regions and blue stellar objects in the northeast halo of NGC 5128. Osmer, P. S. Abstract Observations with an image-tube spectrograph and SIT vidicon system of compact H-alpha knots and blue stellar objects (BSOs) at distances between 13 and 24 kpc from the nucleus of the peculiar elliptical galaxy NGC 5128 are reported. The data for two BSOs are shown to be entirely consistent with the objects' being early-type supergiants having respective absolute magnitudes of -8.8 and -7.5. The brightest H-alpha knot is identified as a typical galactic H II region of moderate excitation. It is found that three other H-alpha condensations have quite complex spatial and velocity structure, exhibit properties typical of H II regions, but are characterized by unusually high degrees of ionization. The origin of the ionized gas is briefly considered. Publication: The Astrophysical Journal Pub Date: December 1978 DOI: 10.1086/182835 Bibcode: 1978ApJ...226L..79O Keywords: Early Stars; Galactic Structure; Microwave Emission; Radio Sources (Astronomy); Supergiant Stars; H Alpha Line; H Ii Regions; Hydrogen Ions; Nebulae; Peculiar Galaxies; Stellar Radiation; Ubv Spectra; Astronomy; Early-Type Supergiants:Galaxies; Galaxies:H II Regions; Galaxies:Radio Sources full text sources ADS | data products SIMBAD (6) NED (1)

Spectral evolution of Nova V400 Per (1974) and Nova V373 Sct (1975)

Photographic and spectroscopic observations of the two galactic novae, V400 Per and V373 Sct, which appeared in 1974 and 1975, have been carried out at Asiago. The light curves of the two novae were characterized by the presence of brightness oscillations during the early decline. The spectral evolution was quite normal: the spectra showed at first, over a relatively strong continuum, wide emission bands of moderate excitation, accompanied by blueshifted absorptions, with radial velocities of −1760 km s−1 (Nova Per) and −1260 km s−1 (Nova Sct). Later, after the novae entered the nebular stage, the continuum weakened, the absorption disappeared and the novae displayed the usual emission spectrum, with permitted and forbidden lines of high excitation ([Oiii], Niii, Hei, Heii). Forbidden lines of Fevi and Fevii-and in Nova Sct, also Fex and Ax-were present for a time, but they soon disappeared, so that at the end the spectrum was dominated by the [Oiii] nebular lines, even stronger than Hα.

Surface photoeffect for metals: Energy and angular electron distributions

The nonlocal theory of the author for the surface photoeffect produced in metals by $p$-polarized light is used to obtain energy and angular electron distributions for a range of low to moderate excitation energies. Considering only the effects from single-particle excitations, the energy distribution curves have, in general, a roughly triangular shape with the peak occurring for initial states near the Fermi energy. There is also a high-energy tail due to damping. Features in the angular distribution curves include confinement to decreasing angles with increasing light frequency and low-angle structure resulting from damping. Very striking structure appears in the energy-resolved angular distributions when the light frequency $\ensuremath{\omega}$ is such that $\ensuremath{\hbar}\ensuremath{\omega}g{E}_{F}+\ensuremath{\Phi}$ where ${E}_{F}$ is the Fermi energy and $\ensuremath{\Phi}$ the work function. A number of significant changes, including a sharp increase in the total yield, occur in the various distributions when Landau damping sets in, that is, when the plasmon enters the single-particle-excitation region. Arguments are presented that there is no reason to expect that the nonlocal surface contributions to the yield should vanish above the plasma frequency.

Effect of thyrotropin-releasing hormone (TRH) and antidepressant agents on brain stem and hypothalamic multiple unit activity in the cat

The EEG and MUA (multiple unit activity) of mesencephalic reticular formation (MRF), area hypothalami posterior (PH), and area hypothalami anterior (AH) were studied in chronically implanted freely moving cats. The effects of thyrotropin-releasing hormone (TRH) and some antidepressant agents were tested on neuronal activity. Desipramine and imipramine resulted in a dose-dependent decline of MUA of all structures with the most significant decrease of activity in PH. A single injection of TRH resulted in slight or moderate gross behavioral changes and vegetative excitation lasting for 30-50 min with variable MUA levels. In the course of repetitive TRH treatment on consecutive days the gross behavioral changes and the vegetative symptoms failed to develop by the 3rd or 4th day. By that time the MUA changes of PH and MRF showed similar characteristics in response to TRH administration which was observed following the injection of desipramine and imipramine. The drugs, except for TRH, induced a suppression of paradoxical sleep cycles.

Excited States in Odd Sn Nuclei, A = 109-125

Gamma-ray and internal conversion studies of the odd Sn isotopes investigated through (α,n) and (d,p) reactions are reported. A level scheme is proposed for each nucleus. An odd parity state at moderate excitation energy above the 1h11/2 single quasiparticle state is identified or proposed in each nucleus, some of which are observed for the first time. Individual level structure and the level systematics in the odd tin isotopes are discussed.

Measurement of pre- and post-fission neutron emission at moderate excitation energies

Fission fragment mass-energy distributions and the coincident neutron velocity distributions have been measured at 0\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} with respect to the fragment direction. The fissioning systems studied were $^{209}\mathrm{Bi}$, $^{232}\mathrm{Th}$, $^{233}\mathrm{U}$, $^{238}\mathrm{U}$, and $^{239}\mathrm{Pu}$ bombarded with 45 MeV $\ensuremath{\alpha}$ particles and $^{226}\mathrm{Ra}$ bombarded with 16 MeV protons. From the above measured quantities the number of pre-fission neutrons and the number of post-fission neutrons were obtained as a function of fragment mass and total fragment kinetic energy. The average number of pre-fission neutrons emitted is 2.9\ifmmode\pm\else\textpm\fi{}0.9 for the $^{232}\mathrm{Th}$ target, 3.3\ifmmode\pm\else\textpm\fi{}1.5 for $^{233}\mathrm{U}$, 3.6\ifmmode\pm\else\textpm\fi{}1.6 for $^{238}\mathrm{U}$, and 2.7\ifmmode\pm\else\textpm\fi{}0.8 for $^{239}\mathrm{Pu}$. The average number of post-fission neutrons emitted by these systems is 4.4\ifmmode\pm\else\textpm\fi{}0.3, 4.2\ifmmode\pm\else\textpm\fi{}0.7, 4.6\ifmmode\pm\else\textpm\fi{}0.7, and 5.1\ifmmode\pm\else\textpm\fi{}0.3, respectively. (The values reported for pre-fission neutrons include also contributions from scission neutrons.) The number of pre-fission neutrons from the $^{226}\mathrm{Ra}$ + 16 MeV proton system is 0.5\ifmmode\pm\else\textpm\fi{}0.3. The number of post-fission neutrons is 3.6\ifmmode\pm\else\textpm\fi{}0.4. The number of neutrons emitted from the $^{209}\mathrm{Bi}$+45 MeV $\ensuremath{\alpha}$ particle system is 3.6\ifmmode\pm\else\textpm\fi{}0.2. The number of post-fission neutrons as a function of fragment mass and total kinetic energy which were obtained by the direct neutron measurements of this work are lower and are more consistent with calculated total energy balances than the values obtained by the indirect method based on the simultaneous measurement of both the kinetic energy and the velocity of the fission fragments. Our results for the average number of pre-fission neutrons are compared with calculations based on the conventional expression for $\frac{{\ensuremath{\Gamma}}_{f}}{{\ensuremath{\Gamma}}_{n}}$. The agreement between the calculated results and our experimental results is satisfactory. However, the calculations predict spallation cross sections which are much larger than those obtained experimentally by radiochemical methods.NUCLEAR REACTIONS, FISSION $^{209}\mathrm{Bi}(\ensuremath{\alpha}, f)$, $^{232}\mathrm{Th}(\ensuremath{\alpha}, xnf)$, $^{233,238}\mathrm{U}(\ensuremath{\alpha}, xnf)$, $^{239}\mathrm{Pu}(\ensuremath{\alpha}, xnf)$, $E=45$ MeV; $^{226}\mathrm{Ra}(p, xnf)$, $E=16$ MeV; measured coin. fragment energy, neutron velocity at $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}$ with respect to fragment; deduced number of pre-fission, post-fission neutrons.

Extracellular potassium activity, intracellular and extracellular potential responses in the spinal cord.

1. Microcapillary electrode assemblies of two or three channels were used to record extracellular and intracellular potentials together with the extracellular activity of potassium ions, from essentially single locations within the substance of the decapitate spinal cord of cats. A liquid ion exchanger filled the tip of the potassium sensing microprobe. Activity was evoked by electrical stimulation of afferent peripheral nerves (ventral roots were cut). 2. Within the substance of the spinal grey matter increments of extracellular potassium activity evoked by repetitive afferent volleys were precisely correlated with magnitudes of sustained shifts of extracellular electric potential. Raising [K+]o from 3 to 4 mM was associated with a negative shift of potential of 2-5 +/- 0-5 mV, regardless of the position of the electrode in the tissue, and regardless of treatment by convulsant or depressant drugs. 3. The spatial distribution of the responses of potassium activity was mapped by the spatial distribution of the negative sustained potential shifts. 4. Depolarization shifts of potential recorded from within neuroglia cells ran parallel with changes of extracellular potassium potential. Even though the magnitude of extracellular sustained potential shifts was precisely correlated with the responses of both extracellular potassium and intracellular glial potentials, the trajectory of sustained potential shifts did not exactly mirror the two other variables. Onset and offset of sustained potential shifts were faster than those of glial potentials or of extracellular potassium. 5. The responses of the true transmembrane potential (intracellular less extracellular potential shifts) of neuroglia cells in the spinal grey matter can fully be described by the Nernst equation. 6. Membrane potentials of neurones, potentials recorded from dorsal root filaments, or from white matter, appeared unrelated to the activity of potassium ions in extracellular fluid. 7. The results are compatible with the suggestions that changes of the membrane potential of spinal neuroglia cells are fully determined by the change of the activity of extracellular potassium, and that glia cells supply most of the current which generates sustained shifts of the extracellular potential of spinal grey matter. The results are hard to reconcile with suggestions that under conditions of moderate excitation (i.e. in the absence of convulsive neuronal activity) changes of extracellular potassium would significantly influence the membrane potential of spinal neurones, or of primary afferent nerve fibres.

Statistical properties of excited fissioning nuclei

The phenomenon of the disappearance of the shell effects on the thermodynamic properties of nuclei with increasing excitation energy has been examined quantitatively on the basis of numerical calculations based on realistic shell model single particle level schemes. It is shown that shell effects disappear at moderate excitation energies and above these excitation energies, the thermodynamic behaviour of the nucleus is identical to that of the equivalent liquid drop model nucleus. Implications of the above feature in the interpretation of some aspects of fission of excited nuclei such as mass-asymmetry and angular anisotropy are examined. The relationship of the phenomenon of washing out of shell effects at high excitation energies with the temperature smearing method of determining ground state shell correction energies is also outlined.

Spectroscopic Observations of Nova Cephei 1971

Spectroscopic observations of Nova Cep 1971 in the visual and infrared regions were carried out at Asiago from July to December 1971. The spectra were characterized at first by the presence of wide emission bands of moderate excitation (H, OI, NI, FeII) accompanied by two absorption systems with mean radial velocity −1300 km s−1 and −2200 km s−1. The velocity was increasing with time. The absorption spectrum disappeared in September and soon the nova entered the nebular stage. The HeI flash was observed in mid-September. In the following months the degree of excitation was steadily increasing. The nebular [OIII] lines became outstanding, even stronger than Hα and the spectrum was characterized by forbidden and permitted lines of relatively high ionization potential (O II, O III, N II, N III, He II).The profiles of the emission bands were complex from the beginning, with a strong central peak. Later, most of the bands split into two separate components, with radial velocities ± 1360 km s−1.The light curve was that of a relatively fast nova. The minimum, B∼ 17.5, was attained in the first half of 1973.