共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary Infrared spectroscopy can greatly help in the understanding of the active galaxies phenomena, having the advantage over optical
and UV spectroscopy of penetrating those nuclei heavily obscured by absorbing dust. The standard photoionization code CLOUDY
by Ferland has been used to predict the intensities of the infrared ionic fine-structure lines. Examples of line ratio diagrams
are presented which constrain the two main free parameters of the models (gas density and ionization parameter), and separate
line emission in the different regions of active galaxies (Seyfert and LINER type nuclei, coronal emission region, starbursts).
Moreover, some line ratio diagrams can disentangle emission-line components from shock excited and photodissociated gas. Finally
we show that the observations of these infrared lines will be possible in the near future with the ISO (Infrared Space Observatory)
spectrometers.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献
2.
Summary We present the first results of an observational programme to identify star forming regions and to provide the near-infrared
energy distributions of embedded objects selected by their IRAS colours.
Based on data collected at the European Southern Observatory, La Silla, Chile. 相似文献
3.
Y. Apeloig D. Bravo-Zhivotovskii M. Yuzefovich M. Bendikov A. I. Shames 《Applied magnetic resonance》2000,18(3):425-434
Electron paramagnetic resonance (EPR) spectroscopy was fruitfully used for studying the formation and the reactions of the star polysilane radical (Me3SiMe2Si)3Si (1).1, which was successfully generated both thermally and photochemically from a variety of precursors, was found to be significantly more stable kinetically than the (Me3Si)3Si radical. Thus, (Me3SiMe2Si)3Si⋅ has a half-life time of ca. 6 min at 20°C, while (Me3Si)3Si⋅ can be observed only at −25°C. Density-functional quantum-mechanical calculations show that1 and (Me3Si)3Si⋅ have the same thermodynamic stability. The high kinetic stability of1 is attributed to its backfold “umbrella”-type conformation where the β-silyl groups point “inwards” towards the radical center. This conformation protects the radical center of1 from dimerization and other reactions. The EPR spectrum of1 and in particular the Si α-hyperfine coupling constant of 5.99 mT shows that1 is less pyramidal than (Me3Si)3Si⋅ but is more pyramidal than (i-Pr3Si)3Si⋅, with an estimated SiSiSi bond angle around the radical center of 118∘. Photolysis and thermolysis of [(Me3SiMe2Si)3Si]2 also involves the intermediacy of1. Photolysis of [(Me3SiMe2Si)3Si]2 leads to (Me3SiMe2Si)4Si, while thermolysis produced the less strained isomer of 1, (Me3SiMe2Si)3SiSi-Me2Si(Me3SiMe2Si)2SiMe3. In this study we provide the first direct evidence that silyl radicals are involved as intermediates in the reactions of silanes with di(tert-butyl)mercury. 相似文献
4.
文章简要叙述了有关大质量恒星形成的理论以及相关观测证据.目前大质量恒星形成的理论主要有两种,即吸积说和并合说.吸积说认为,大质量星可能与小质量星形成于相似的过程;并合说主张大质量星可能是由小质量年轻星碰撞合并而成.解决这两种理论争论的关键在于在大质量星附近能否观测到吸积盘的存在,最新的观测表明大质量星更有可能是通过吸积增加自身的质量,但最终解决这一问题可能还需要更多的观测证据.文章还提出了一些本领域尚未解决的问题,为感兴趣的研究者提供参考. 相似文献
5.
文章简要叙述了有关大质量恒星形成的理论以及相关观测证据。目前大质量恒星形成的理论主要有两种,即吸积说和并合说.吸积说认为,大质量星可能与小质量星形成于相似的过程;并合说主张大质量星可能是由小质量年轻星碰撞合并而成.解决这两种理论争论的关键在于在大质量星附近能否观测到吸积盘的存在,最新的观测表明大质量星更有可能是通过吸积增加自身的质量,但最终解决这一问题可能还需要更多的观测证据。文章还提出了一些本领域尚未解决的问题,为感兴趣的研究者提供参考。 相似文献
6.
Star formation lies at the center of a web of processes that drive cosmic evolution: generation of radiant energy, synthesis of elements, formation of planets, and development of life. Decades of observations have yielded a variety of empirical rules about how it operates, but at present we have no comprehensive, quantitative theory. In this review I discuss the current state of the field of star formation, focusing on three central questions: What controls the rate at which gas in a galaxy converts to stars? What determines how those stars are clustered, and what fraction of the stellar population ends up in gravitationally-bound structures? What determines the stellar initial mass function, and does it vary with star-forming environment? I use these three questions as a lens to introduce the basics of star formation, beginning with a review of the observational phenomenology and the basic physical processes. I then review the status of current theories that attempt to solve each of the three problems, pointing out links between them and opportunities for theoretical and numerical work that crosses the scale between them. I conclude with a discussion of prospects for theoretical progress in the coming years. 相似文献
7.
E. V. Korolik R. G. Zhbankov A. A. Ivanov G. K. Il’ich N. I. Insarova V. G. Leshchenko 《Journal of Applied Spectroscopy》1998,65(6):906-910
Use of low-temperature IR spectroscopy in studies of compounds with a developed system of hydrogen bonds such as DL-serine
revealed a complete set of vibrational frequencies. The region of manifestation of stretching vibrations of OH groups involved
in the formation of strong hydrogen bonds was found. It is shown experimentally that in a crystal some of the molecules of
SL-serine exist in the nonionized form. On the basis of analysis of experimental data, frequency ranges of stretching deformation
and torsional vibrations of NH
3
+
, COO−, and OH groups were determined more accurately. It is found that in the crystals there exist molecules of DL-serine with
different spatial orientation of NH
3
+
COO−, and COH groups. It is shown that conformational diversity of molecular structures is also preserved at T=18 K.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 864–868, November–December, 1998. 相似文献
8.
T. Nzeyimana E.A. Naji X. Urbain A. Le Padellec 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):315-325
Total cross-sections have been measured for the associative ionisation of C
+
+
O
-
, N
+
+
O
-
and O
+
+
O
-
by means of a merged-beam set-up operating with keV beams. These original measurements might be relevant to the understanding
of some astrophysical objects or laboratory-made plasmas (flames and etching plasmas). The magnitude of these cross-sections
is particularly large whatever the associating system, as these are in the range of 1×10
-14
cm2 at thermal energies. Their behaviour as a function of energy significantly differs from one system to another, and is characterised
by the Wigner law at low energy, and a rapid fall-off at higher energy due to competition with non-associative ionisation
processes.
Received 10 December 2001 and Received in final form 12 March 2002 相似文献
9.
I. Stenger B. Gallas L. Siozade S. Fisson G. Vuye S. Chenot J. Rivory 《Physica E: Low-dimensional Systems and Nanostructures》2007,38(1-2):176
SiOx films (1<x<2), 0.5 μm thick, have been elaborated by electron-gun evaporation. A thermal annealing of these films induced a phase separation leading to the formation of Si nanocrystals embedded in a SiO2 matrix. These films have been studied by infrared spectroscopic ellipsometry and by X-ray photoelectron spectroscopy (XPS). The effective dielectric function of the thin films has been extracted in the 600–5000 cm−1 range which allowed us to deduce the dielectric function of the matrix surrounding the Si-nc. A study of the Transverse Optical (TO) vibration mode has revealed the presence of SiOx into the matrix. Before XPS measurements, the films have been etched in fluorhydric acid to remove the superficial SiO2 layer formed during air exposure. The Si 2p core-level emission has been recorded. The decomposition of the Si 2p peak into contributions of the usual five tetrahedrons Si-(Si4−nOn) (n=0–4) has also revealed the presence of a SiOx phase. Consistency between infra-red and XPS results is discussed. 相似文献
10.
R. Le Parc A. Piarristeguy N. Frolet M. Ribes A. Pradel 《Journal of Raman spectroscopy : JRS》2013,44(7):1049-1057
Agx(Ge0.25Se0.75)100−x glasses with x varying from 0 to 25 have been shown to exhibit a conductivity threshold around x ~8–10. In this work, the structural changes induced by introduction of Ag in Ge25Se75 glass have been investigated using Raman and infra‐red spectroscopies. In ambient conditions, changes are observed in position, width and intensity for vibrations assigned to Ge–Se bonds, showing that the tetrahedral network is relaxed and gains flexibility as Ag is introduced. High pressure experiments on two glasses containing 5 and 25 at.% Ag confirm that Ag‐rich (25%) glasses clearly exhibit higher compressibility than Ag‐poor (5%) glasses. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
11.
A. J. Barger 《Contemporary Physics》2017,58(2):160-175
Our primary means of studying how galaxies form and evolve over cosmic time is through measurements of the rate at which massive stars are born in galaxies per unit comoving volume of the universe. Only recently have the most distant, most massively star-forming galaxies in the universe even been discovered, and these discoveries are challenging the standard cosmological scenario in which galaxies form hierarchically, with low-mass objects collapsing first and then merging to form larger and larger systems over cosmic time. We now know that these incredibly luminous galaxies, which have all but vanished in the local universe, are cocooned in dust, hiding them from optical view. They can only be detected at long wavelengths where the dust reradiates the starlight that it has absorbed. In this review, I trace the spectacular progress that has been made over the last decade towards understanding the cosmic history of star formation, with a particular emphasis on the important role of dusty sources in that history. 相似文献
12.
E. Buixaderas D. Nuzhnyy S. Veljko M. Savinov P. Vaněk S. Kamba 《Phase Transitions》2013,86(6-7):415-426
The dielectric behaviour of tetragonal PLZT x/40/60 ceramics doped with lanthanum (x?=?5,?12 and 15%) has been investigated at 100–1014?Hz. Dielectric, THz and infrared spectra were measured from 500 to 20?K. For x?≥?12 relaxor ferroelectric behaviour was observed. All three samples showed an additional relaxational mode below phonons. Analysis of the phonon modes for ferroelectric PLZT 5/40/60 is presented together with the complete dielectric behaviour. 相似文献
13.
A. Maignan C. Martin M. Hervieu B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):41-45
The substitution of manganese for cobalt in the perovskite La
0.8
Sr
0.2
CoO
3
has been studied. A significant increase of the magnetoresistance (MR) is obtained, reaching 60% at 5 K under 7 T for . This behavior originates from a spectacular increase of the resistivity correlated to a significant decrease of ferromagnetism
by Mn doping. This enhancement of magnetoresistance can be interpreted by the growth of ferromagnetic clusters in the insulating
matrix, by applying a magnetic field.
Received 7 May 1999 相似文献
14.
D. Barba S. Jandl A.A. Martin C.T. Lin M. Cardona T. Wolf 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):277-281
Infrared reflectance, and transmission measurements as well as Raman scattering have been used to study the RE1+xBa2-xCu3O6 (RE = Nd, Sm) and YBa2Cu3O6 absorption bands in the 1100-1500 cm-1 infrared range as a function of temperature and beam polarization. In addition to two-phonon absorption between 1100 and
1170 cm-1, we observe excitations around 1400 cm-1, occurring in oxygen rich enclosures within the samples, and assign them to an excitation involving two-phonons plus the
270 cm-1 local mode related to Cu-O broken chains. Thus, the previously reported possible magnetic origin of the 1436 cm-1 sharp absorption band in YBa2Cu3O6 is contested.
Received 14 February 2001 and Received in final form 12 April 2001 相似文献
15.
Humans have always dreamt about the possibility of existence of planets in solar systems other than our own. After flying by, dropping probes, and even landing devices on most planets within our own solar system, the search for extra-solar planet is included in every proposal to either build a larger and better earth-, space-, or moon-based telescope, or observatory facility. The preliminary analysis seems to indicate that wavelength band from 25 μm to 30 μm is most promising in solving this problem. A number of IR technological challenges are to be overcome before the actual detection system can even be considered in a detailed design. The significant technical challenges of finding a planet will be described. Then details are given on the feasibility of detecting a planet with an instrument concept designed specifically for this purpose, a space-based, rotating rotationally shearing interferometer. 相似文献
16.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
17.
J. Dec W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):627-632
The complex dielectric susceptibility of Sr
0.61
Ba
0.39
Nb
2
O
6
:Ce
3+
(SBN61:Ce) has been measured at frequencies and temperatures before and after poling. The relaxor behaviour with large polydispersivity observed above the ferroelectric phase transition
temperature, T
c
= 360 and 340 K for x
(Ce) = 0 and 0.0066, respectively, is perfectly modeled within the framework of Chamberlin's dynamically correlated domain approach.
Below T
c
the dynamic nanodomain state crosses over into a ferroelectric state with polydispersive domain wall dynamics at very low
frequencies. Presumably SBN61:Ce belongs to the three-dimensional random field Ising rather than to the dipole glass universality
class.
Received 1 October 1999 相似文献
18.
M. Gaudry J. Lermé E. Cottancin M. Pellarin B. Prével M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):201-204
Optical properties of mixed clusters (AuxAg
1 - x
)
n
and (NixAg
1 - x
)
n
, produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different
concentrations (x
= 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg
1 - x
)
n
of a given size an almost linear evolution of the surface plasmon frequency ω
s
with the concentration is observed (between those of pure gold and pure silver clusters). Moreover the blue-shift and the
damping of the resonance with decreasing size is all the more important as the gold concentration in the particles increases.
Such results are in agreement with theoretical calculations carried out in the frame of the time-dependent local-density-approximation
(TDLDA) including an inner skin of ineffective screening and the porosity of the matrix. The optical response of (NixAg
1 - x
)
n
clusters exhibits a surface plasmon resonance in the same spectral range as the one observed for pure silver clusters, but
considerably damped and broadened. For a given mean cluster size 3.0 nm, a blue-shift of the resonance is observed when increasing
the nickel concentration (between x
= 0.25 and x
= 0.75). The results are in good qualitative agreement with classical predictions in the dipolar approximation, assuming a core-shell
geometry.
Received 21 November 2000 相似文献
19.
The influence of boron (B)/arsenic (As) on X-ray photoelectron spectroscopy (XPS) study of NiSi formation on shallow junctions is investigated in this paper. The Ni-silicide film was formed after 30 s soak anneal at 450 °C on ultra shallow p+/n or n+/p junctions. The atomic ratio of Ni/Si profile in depth was probed by XPS and the results show that a uniform NiSi layer forms on B-doped p+/n junction while a non-uniform, Ni-rich silicide layer forms on As-doped n+/p junction. It does not agree with the results of other independent phase identification methods such as X-ray diffraction, Rutherford backscattering spectroscopy, and Raman scattering spectroscopy, which all demonstrate the formation of NiSi on both n+/p and p+/n junctions. Comparing the raw binding energy spectra of Ni and Si for each silicide film, the similar spectra for Ni signals are revealed. But the Si signals with an obviously smaller intensity is found to be responsible for the apparent Ni rich silicide formation on As-doped n+/p junction. It indicates that As atoms in the silicide film can affect the sputtering yield of Ni and Si, while no noticeable effect is observed for B atoms. More As atoms than B atoms segregation into the silicide layer is indeed verified by secondary ion mass spectroscopy. And micro-Raman scattering spectroscopy further confirms that the degree of crystallinity for NiSi on n+/p junction is inferior to that on p+/n junction. 相似文献
20.
F.S. da Rocha G.L.F. Fraga D.E. Brand?o C.M. Granada C.M. da Silva A.A. Gomes 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):307-311
The magnetic moment of the Mn impurities was obtained from magnetization measurements of Y
(
Ni
1 - x
Mn
x
)
2
B
2
C as a function of the concentration x less than 0.15. Using the coherent potential approximation and starting from 3
d density of states, obtained from the first principles calculations, the magnetic moments are obtained within a two sublattice
model. For adequately estimated values of the Coulomb interactions U, the position of the energy level of Mn and adopting values for the intersublattice hybridization term, a qualitative agreement
with the observed experimental data is obtained.
Received 23 April 2001 and Received in final form 29 October 2001 相似文献