微波多普勒反射计数据分析的一种优化方法

结合对多普勒频谱的分析,提出一种基于双高斯拟合的轴对称-非对称谱(SAS)分析方法。在此方法下,功率谱主要由轴对称功率谱和非轴对称功率谱两部分组成。前者主要由等离子体截止层密度的扰动调制决定,后者主要由波数为k _⊥=2k₀sinθ 的湍流的极向密度扰动决定。在分析多普勒反射计的数据时,相较于常用的频谱重心(COG)分析方法和相位微分(δ-phase)法,SAS 谱分析不仅提高了求取多普勒频移的准确性,同时还可以获取等离子体中波数为k_⊥ 的极向湍流的密度扰动强度和截止层的密度扰动强度。     

The dependence of muon intensity on the geomagnetic latitude

The vertical momentum spectrum of cosmic-ray muons has been determined by a counter controlled neon-hodoscope in the spectral region (0.2–3) Bev/c at geomagnetic latitude 12 °N. The observed spectrum agrees satisfactorily with the calculated spectrum of Olbert for muon momentum above 1.8 Bev/c. Below about 1.8 Bev/c, the measured spectrum exceeds slightly the theoretical spectrum of Olbert, calculated for the same geomagnetic latitude. The measured spectrum agrees with the experimental spectrum of Allkofer at 9 °N, but is somewhat below the spectrum obtained by Hayman in the low momentum region at 57.5 °N. This shows that there exists a latitude dependence of the low momentum muon spectrum. The estimated integral intensity of muon of momentum ≧320 Mev/c is found to be 7.3×10^?3 cm^?2 sec^?1 str^?1 which agrees with the value of other investigators^1–9.     

On the electronic spectrum of low-dimensional structures with the symmetry of borders

The features of the electronic spectrum in low-dimensional (quasi-one-dimensional) structures with symmetry of borders have been considered. It has been shown that, in the spinless case, the conical massless (Dirac) form of the spectrum (ɛ(k) ∝ ± |k|) appears in groups with glide planes. This spectrum is a consequence of forced degeneracy, which appears due to the joint action of the lattice symmetry elements and time reversal invariance. For the spinor representations, the conical shape of the spectrum appears in all groups.     

Charged excitons at high magnetic fields: the effect of the surrounding electron gas

We study the photoluminescence (PL) spectrum of a two-dimensional electron system at the high magnetic field limit, where all electrons reside at the lowest Landau level (ν<2). Using a gated structure we tune the electron density from the dilute limit to a dense electron gas, and follow the changes in the emission spectrum. We find that the spectrum at the dilute limit consists of two bound triplets, whose behavior is consistent with that of the dark and bright triplets. We show that the spectrum undergoes critical changes at ν=1/3, from an isolated charged exciton-like spectrum at ν<1/3, to a spectrum that reflects the interactions with the surrounding electrons above this filling factor. This behavior is found to be robust, independent of the electron density and magnetic field. We compare our observations with other recent low temperature PL measurements of a two-dimensional electron gas at high magnetic field and find good agreement and consistency.     

团簇红外吸收谱的理论研究

根据时间关联函数理论，可以结合分子动力学模拟而计算团簇的红外吸收谱. 应用正交紧束缚分子动力学模拟，计算了C₆₀的红外吸收谱. 结果与实验相符，足以识别团簇 体系的红外吸收谱. 这将是研究纳米团簇体系的有力理论分析工具. 关键词： 红外吸收谱 团簇 时间关联函数     

Quantum corrections to the spectroscopy of a BTZ black hole via periodicity

Quantum corrections to the area spectrum and the entropy spectrum of a BTZ black hole are calculated by equaling the motion period of an outgoing wave coming from the quantum corrections of the semiclassical action to the period of gravitational system with respect to the Euclidean time. We find that the area spectrum and the entropy spectrum are independent of the properties of particles. Furthermore, in the presence of higher-order quantum corrections, the area spectrum is found to be corrected by inverse area terms while the entropy spectrum is found to have a universal form, $\varDelta S_{BH}=2\pi $ . Both results show that the entropy spectrum is independent of not only the BTZ black hole parameters but also the higher-order quantum corrections, which implies that the entropy spectrum is more natural than the area spectrum in quantum gravity theory.     

Influence of the substrate structure on the bonding of chemisorbed acetylene to transition metal surfaces

The electronic spectrum of acetylene adsorbed on various transition metals has been measured by ultraviolet photoemission spectroscopy in various laboratories. At low temperatures (T < 150 K), all measurements concur in finding an electron spectrum that differs only moderately from the gas phase spectrum of acetylene. At room temperature, the electron spectrum of acetylene is reported to be similar to the low-temperature form on Ir(100) and Pt(100), but acetylene is reported to form an olefinic surface complex on Pd(111) and Pt(111) surfaces. In order to examine whether the surface structure of the substrate is responsible for the difference, we have measured the electronic spectrum of acetylene adsorbed on the Pd(100) and Ru(0001) surfaces. At 120 K, the spectrum of adsorbed acetylene is again a distorted gas phase spectrum on both surfaces. At 330 K, we find the acetylenic form (with a splitting of 2.5 eV of the σ-orbitals) on Pd(100) and an olefinic form on the basal plane of Ru. We conclude that the olefinic complex is proper to the threefold symmetry of the (111) and (0001) surfaces and the gas-like form is favored on the (100) surfaces of the fcc crystals.     

On the influence of the trapping of particles on the beam-plasma interaction

Interaction of the trapped beam particles with spectrum is discussed in the paper. In models of particles in two waves and in a spectrum (with given amplitudes) we discuss partly well trapped particles (in the region of harmonic oscillations), partly weakly trapped particles near the separatrix; further, we discuss the range of resonances, the transport of energy and a possibility of transition of the trapped beam into the quasiergodic state. For the case of a discrete spectrum, conditions for the beam diffusion are given and, within the framework of system with mixing, conditions for existence of hf field-beam particles balance are discussed.Nademlýnská 600, Praha 9, Czechoslovakia.     

Characteristic features of the energy spectrum of icosahedral quasicrystals

The character of the energy spectrum of an icosahedral quasicrystal is investigated in the tight-binding approximation. It is found that the spectrum does not contain the hierarchical gap structure characteristic for a Cantor set. Investigation of the smoothness of the energy spectrum by the method of level statistics showed that the spectrum contains a singular part. Suggestions are made concerning the form of the wave functions. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 101–105 (25 January 1996)     

Magnetopolaron states of a spin-correlated antiferromagnet in the neighborhood of the spin-glass transition

The problem of the spectrum of magnetopolaron states of a strongly correlated conducting canted antiferromagnet is solved. The approach used to study the spectrum is based on an atomic representation and a diagram technique for Hubbard operators. This approach makes it possible to include strong intra-ion interactions in a first-principles way, and to obtain the dispersion equation for the magnetopolaron spectrum for arbitrary values of the magnitude of the spin, temperature, and magnetic field. In the vicinity of the spin-flip transition an analytic expression is obtained for the spectrum of magnetopolaron states that goes beyond the framework of the quasiclassical approximation. Fiz. Tverd. Tela (St. Petersburg) 40, 310–314 (February 1998)     

Influence of the humidity conditions on the reflectivity spectrum of a porous silicon microcavity

We have designed and fabricated a porous silicon (PS) microcavity that shows a reflectivity resonance around 3 μm in between two spectral regions with high reflectivity values. The microcavity has been simulated following the photonic crystals formalism, which results in good agreement with the measured spectrum. The reflectivity spectrum of the microcavity has been analyzed under different humidity conditions. We demonstrate that the reflectivity resonance shifts to higher wavelengths and that the reflectivity decreases when the humidity increases. In addition, the reflectivity spectrum of the as-prepared device is recovered when the humidity returns to the initial laboratory conditions. Finally, the effect on the reflectivity spectrum of a condensed water layer at the surface of the microcavity is also analyzed.     

Rotational spectroscopy of the first excited state of the acetylenic C-H stretch of 3-fluoropropyne performed by infrared-Fourier transform microwave-microwave triple-resonance spectroscopy

The rotational spectra of 3-fluoropropyne in the ground and first excited acetylenic C-H stretch vibrational state have been measured. The pure rotational spectrum of the normal species and the ¹³C isotopomers were measured using FTMW-cwMW double-resonance spectroscopy based on the Autler-Townes (AC Stark) effect. The lineshape properties of this measurement make it possible to determine the transition strength, ΔJ-selection rules, and the relative energy ordering of the quantum states. The frequency accuracy of this technique is tested against a previous pure rotational study of 3-fluoropropyne. The rotational spectrum of vibrationally excited state was obtained through IR-FTMW-cwMW methods. In this technique a single-longitudinal-mode pulsed infrared laser source vibrationally excites the acetylenic C-H stretch with J-selectivity. The rotational spectrum of the excited state is then obtained by FTMW and FTMW-cwMW double-resonance methods. The excited-state measurements have a signal-to-noise ratio comparable to the pure rotational spectrum. The residuals in the excited-state fit are larger than those obtained in the ground-state fit. This greater deviation from a standard asymmetric top spectrum is most likely due to weak perturbations to the acetylenic C-H spectrum.     

Interpretation of the soret band of porphyrins based on the polarization spectrum of N-methyltetraphenylporphin fluorescence

Low-temperature (77 K) absorption, fluorescence, and fluorescence-excitation spectra and the fluorescence polarization spectrum for N-methyl-meso-tetraphenylporphin (N-methyl-TPP) are measured. Based on the polarization spectrum the absorption spectrum in the visible region (a “generic” porphyrin spectrum) is interpreted. In particular, it is shown that the fifth absorption band (the “Longo band”) that manifests itself in some porphyrins is a Q_y(0–2) band and does not belong to the individual electron transition. Emphasis is placed on the region of the Soret band. It is inferred that at least two allowed electron transitions (G →B_x and G→B_y) polarized mutually perpendicularly manifect themselves in this region. The interpretation of the Soret band of porphyrins [2] that attributes this band to one electron transition G→B_x is thereby rejected. This interpretation is confirmed by computer modeling of the polarization spectrum. Special features of the experimental polarization spectrum are explained by a more developed vibrational structure and, possibly, a larger half-width of the B_x band than the half-width of the B_y band. The contribution of the states of intramolecular charge transfer to the formation of the Soret band is discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 65–72, January–February, 1999.     

On the finiteness of the discrete spectrum of four-particle lattice Schrödinger operators

A Hamiltonian describing four quantum mechanical particles (bosons) moving on a lattice is considered. The corresponding Fredholm's integral equations of the Faddeev-Yakubovskii and Weinberg type are obtained and the location and structure of the essential spectrum are studied. The finiteness of the discrete spectrum for all interactions and the absence of eigenvalues lying outside the essential spectrum for the case of “weak interactions” are proved.     

Neutron events in the underground monitor of the Tien Shan high-altitude station

The neutron multiplicity M spectrum was measured at the neutron monitor installed in the underground room of the Tien Shan high-altitude station (3340 m above sea level) of the Lebedev Physical Institute under a ground layer 20 m of water equivalent thick. To a first approximation, the differential multiplicity spectrum is power-law: dN/dM = 0.3 · M^−3.7m⁻²s⁻¹. The spectrum intensity is lower than the intensity of events in the ground-based NM64 supermonitor by a factor of 350–450. The spectrum slope exponent γ + 1 = 3.7 ± 0.1 is identical to the exponent of the energy spectrum of bremsstrahlung gamma-rays of energetic muons (above 1 TeV) generated in a lead absorber of the monitor. In this case, the experimental intensity is hundred times higher than the expected intensity of events from muon bremsstrahlung. The spatial distribution of neutrons in the monitor suggests that they are produced by single particles. The temporal distribution of neutrons in the monitor is exponential with lifetime constant τ = 360 − 390 μs. Difficulties are indicated in the interpretation of the multiplicity spectrum by electromagnetic and nuclear interactions of muons in the monitor without involving new penetrating particles. Original Russian Text ? A.P. Chubenko, A.L. Shchepetov, L.I. Vildanova, M.I. Vildanova, P.A. Chubenko, 2007, published in Kratkie Soobshcheniya po Fizike, 2007, Vol. 34, No. 4, pp. 21–31.     

Some Special Features of the Concentration Dependence of the Quasi-Line Spectrum Intensity

The nonlinearity mechanisms of the concentration dependence of the quasi-line spectrum intensity are investigated for 1,2-benzpyrene in n-hexane. It is established that redistribution of molecules over the energy levels, caused by the effect of internal filter created by substituted impurity molecules, can contribute significantly to changes in the spectrum intensity. It is demonstrated that this effect can cause redistribution of the quasi-line luminescence spectrum intensity for a multicomponent system.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–6, April, 2005.     

On the possibility of reconstructing an anisotropic wind wave spectrum by the method of double-position sonar

We investigate the possibility of reconstructing the wind wave spectrum, with anisotropy taken into account, by the method of ocean acoustic sounding, using horizontally deployed antennas in the continuous mode of operation. This method uses marrow-beam horizontally spaced antennas for radiating a monochromatic sound signal and receiving signals scattered by the surface. By this method, we can localize a definite area of the scattering surface and reconstruct the wind wave spectrum owing to the direct dependence of the wind wave harmonic, which forms the scattered signal, on the position of this area relative to the radiator and the receiver. Expressions that relate the energy spectrum of the scattered signal formed at the receiver output to the wind wave spectrum are found. On the basis of these expressions, an algorithm has been developed for gaining information both about the spatial isotropic spectrum of wind waves and about the dependence of the angular spectrum on the value of the wind wave vector and its direction relative to the wind velocity.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 139–145, January–February, 1995.     

The asymptotic spectrum of the EWMA covariance estimator

The exponentially weighted moving average (EWMA) covariance estimator is a standard estimator for financial time series, and its spectrum can be used for so-called random matrix filtering. Random matrix filtering using the spectrum of the sample covariance matrix is an established tool in finance and signal detection and the EWMA spectrum can be used analogously. In this paper, the asymptotic spectrum of the EWMA covariance estimator is calculated using the Mar?enko-Pastur theorem. Equations for the spectrum and the boundaries of the support of the spectrum are obtained and solved numerically. The spectrum is compared with covariance estimates using simulated i.i.d. data and log-returns from a subset of stocks from the S&P 500. The behaviour of the EWMA estimator in this limited empirical study is similar to the results in previous studies of sample covariance matrices. Correlations in the data are found to only affect a small part of the EWMA spectrum, suggesting that a large part may be filtered out.     

Effect of phasons and magnetic fields on the electronic spectrum of a three-dimensional quasicrystal

The effect of phasons and magnetic fields on the electronic spectrum of an icosahedral quasicrystal is investigated in the tight-binding approximation. Phasons smooth the singular spectrum and produce a greater delocalization of the critical wave functions. A magnetic field shifts the limits of the spectrum, smooths the spectrum, lifts the degeneracy, and also delocalizes the wave functions. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 659–661 (10 May 1999)     

Dependence of the energy spectrum of UHE cosmic rays on the latitude of an extensive air shower array

Several energy spectra of cosmic rays with energies E ₀ ≥ 10¹⁷ eV measured at the Yakutsk EAS, AGASA, Haverah Park, HiRes, Auger, and SUGAR arrays are considered. It is shown that the fairly good mutual agreement of the spectrum shapes can be achieved if the energy of each spectrum is multiplied by a factor K specific for each spectrum. These factors exhibit a pronounced dependence on the latitude of the above-mentioned arrays.