Pressure effects on 2p5 3p - 2p5 3d transitions in neon

The collisional broadening and shift of four spectral lines of neon (747.2, 748.8, 753.5, 754.4 nm) arising from 2p⁵ 3p - 2p⁵ 3d transitions, emitted from a low-pressure glow discharge in pure neon and neon-helium mixtures have been measured using a Fabry-Perot interferometer. The values of pressure broadening and shift coefficients are determined and analyzed in terms of the impact theory.     

Resonant raman effect of hematoporphyrin IX in the α, β absorption band of the Q(π→π*) electronic transition

Summary Resonant Raman spectra of hematoporphyrin IX have been obtained in methanol, acetone and acetic acid. Excitation RR profiles show that intensity enhancements, due to the vibronic excitation process, are active for some normal vibrations of the macrocycle and for motions of the lateral groups. Line-width-lifetime correlations and molecular-association processes are discussed.

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Riassunto Gli spettri di risonanza Raman di ematoporfirina IX sono stati ottenuti in soluzioni di metanolo, acetone e acido acetico. I profili di eccitazione di risonanza Raman mostrano che aumenti d'intensità, dovuti al processo di eccitazione degli stati vibronici, sono osservabili per alcuni modi normali del ?macrociclo? e per alcune vibrazioni di gruppi appartenenti ai sostituenti laterali nel macrociclo. Le correlazioni tra ampiezza di riga e tempo di vita dello stato vibronico, nonché i processi di associazione molecolare, sono discussi nel presente lavoro.

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Резюме Получаются резонансные рамановские спектры для гематопорфирина IX в метаноле, ацетоне и уксусной кислоте. Профили резонансного рамановского возбуждения обнаруживают, что увеличение интенсивности, обусловленные процессами вибрационного возбуждения, являются наблюдаемыми для некоторых нормальных мод ?макроцикла? и для движений поперечных групп. Обсуждаются корреляции между шириной линии и временем жизни и процессы объединения молекул.

     

ROSETTA and FIRST: Two cornerstone missions of ESA long-term space science programme

Summary The paper reviews the objectives and status of definition of ROSETTA (Comet Nucleus Sample Return) and FIRST (Far Infrared Space Telescope), which are two cornerstone missions of the ESA long-term scientific programme. ROSETTA is a joint ESA/NASA programme and it will address problems centered on the origin of planetary material and the pre-biotic evolution of organic matter. The ROSETTA spacecraft will be launched in 2001; it will land into the nucleus of comet Churyumov-Gerasimenko, take about 10 kg of cometary samples (ice, dust, organics) and will return the Earth in 2008. FIRST will explore the 10 μm to 1 mm region of the electromagnetic spectrum, where a large number of very important atomic and molecular spectral lines are hosted. The major scientific objectives are the physics of the interstellar medium of the star formation and cosmological studies. The mission is based on a 4.5 to 8 m telescope equipped with imaging spectrometers and operating as a near-real-time observatory from a high elliptical orbit of 24 h period. Low operating temperatures for the payload will be achieved by using a combination of mechanical coolers and a liquid helium cryostat. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Coherent hyper-raman scattering: An application to amorphous materials

Summary Coherent Hyper-Raman scattering from hot polaritons gives conspicuous advantages with respect to thermal Hyper-Raman scattering. It allows a precise study of polar modes in liquids and amorphous materials, where they are forbidden in Raman scattering. We give a classical theory for this nonlinear process and the results are applied to the study of the polariton at 1065 cm⁻¹ in amorphous quartz. The experimental data, having a precision two orders of magnitude better than in previous studies, show that the polaritons propagate in the glass with a well-defined wave vector. The dispersion curve of the polariton and its width in the wave vector space can be described by means of a multioscillator model taking into account the inhomogenous width of the levels originated from disorder.

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Riassunto La diffusione Hyper-Raman coerente da polaritoni eccitati mediante assorbimento di un impulso laser infrarosso offre notevoli vantaggi rispetto alla diffusione Hyper-Raman termica. Essa consente uno studio preciso dei modi polari negli amorfi e nei liquidi dove risultano proibiti nelle transizioni Raman. Viene formulata una teoria classica per questo tipo di diffusione coerente ed i risultati vengono applicati allo studio sperimentale del polaritone a 1065 cm⁻¹ nel quarzo amorfo. I dati sperimentali, con una precisione di due ordini di grandezza migliore che nei precedenti studi, mostrano che il polaritone si propaga nel vetro con un ben definito vettore d’onda. La curva di dispersione del polaritone e la sua larghezza nello spazio dei vettori d’onda può essere descritta mediante un modello a più oscillatori, tenendo conto dell’allargamento inomogeneo dei livelli derivante dal disordine.

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Резюме Когерентное гипер-рамановское рассеяние на горячих поляритонах дает явные преимущества по сравнению с тепловым гиперрамановских рассеянием. Этот подход поэволяет исследовать полярные моды в жидкостях и аморфных материалах, где они эапрешены при рамановском рассеянии. Мы раэвиваем классическую теорию для этого нелинейного процесса и полученные реэультаты применяются к иоследованию псляритона при 1065 cm⁻¹ в амопфном кварце. Эксперименталвные данные, имеюшие точносты на два порядка лучше предыдуших реэультатов, покаэывают, что поляритоны распространяются в стекле с хорошо определенным волновым вектором. Дисперсионная кривая поляритона и ее шириина в пространстве волновых векторов может быты олисана с помощью многоосцилляторной модели, которая учитывает неоднородную ширину уровней, воэникющую иэ-эа неупорядоченности.

     

FEL gain in the pulsed regime: a comparison between numerical and analytical results

Summary In this paper we present simple and general formulae for the FEL gain in the pulsed regime including both the longitudinal mode coupling and the lethargy effect. Such relations, obtained from a numerical integration of the pulse propagation equations, are then compared to similar expressions obtained analitycally in the limiting case of the long bunch approximation and the agreement is shown to be excellent.

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Riassunto In questo lavoro vengono derivate formule semplici e generali relative al guadagno FEL in regime impulsato. Tali formule tengono conto dell'accoppiamento tra i modi longitudinali e dell'effetto di letargia. Le relazioni di cui sopra sono ottenute nell'ambito di una trattazione numerica delle equazioni di propagazione degli impulsi e sono poi comparate ad analoghe espressioni ottenute per via analitica nel caso limite di pacchetto di elettroni lungo. Si dimostra come l'accordo sia particolarmente buono.

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Резюме В зтой статье мы приводим простые и общие формулы для усиления для лазера на свободных злектронах в импульсном режиме, учитывая связь продольных мод и зффект летаргии. Зти соотношения, полченные с помощью численного интегрирования уравнений распространения импульса, затем сравниваются с аналогичными выражениями, полученными аналитически в предельном случае приближения длинного сгустка, и получается хорошее согласие.

     

The atmosphere of Titan and the Huygens atmospheric structure instrument

Summary The Huygens Atmospheric Structure Instrument (HASI) is a multisensor package which has been designed to measure the physical quantities characterizing the atmosphere of Titan. After a short summary of the available information on Titan's atmosphere, the HASI is described as well as its capabilities to improve our knowledge of the larger Saturnian satellite. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Raman scattering in defect chalcopyrite crystals

Summary Raman-scattering measurements on the defect chalcopyrite compounds CdGa₂Se₄, CdGa₂S₄, ZnGa₂S₄ are reported. The phonon picture is consistent with the space group. A comparison between corresponding phonons suggests a simple model for the vibrational dynamics. Preliminary Raman results in the mixed compound Cd _x Zn_1−x Ga₂S₄ and in resonance conditions in CdGa₂Se₄ are presented. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Decrease in frequency of maximum far-infra-red power absorption of polar fluids with temperature

Summary It is shown how the inherent nonlinearity of the equations of motion of coupled dipoles qualitatively explains a number of features of the observed far-infra-red spectrum of polar fluids. These include the almost linear increasing temperature and the temperature independence of the band width.

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Riassunto Si mostra come l'inerente non linearità delle equazioni di moto di dipoli accoppiati spiega qualitativamente un numero di comportamenti dello spettro osservato nel lontano infrarosso di fluidi polari. Questi includono il decremento quasi lineare della posizione del picco del coefficiente di assorbimento di potenza FIR con l'aumento della temperatura e l'indipendenza della temperatura dell'ampiezza di banda.

     

Raman scattering by hot and thermal polaritons in crystal quartz

Summary Nonlinear mixing of IR and visible radiation,i.e. coherent Raman scattering by polaritons driven by a CO₂ laser, has been used to obtain the dispersion curve and its width inq-space of the polariton associated to theE-phonon at 1065 cm⁻¹ in crystal quartz. It is shown in this paper that a direct method to determine indipendently, with high precision, the refractive index and absorbance of a crystal can be obtained in this way. The results are compared with accurate data obtained from Raman scattering by polaritions in thermal equilibrium and very good agreement is found between the two measurements. It is finally shown that nonlinear-mixing techniques turn out to be completely consistent with the simple picture of scattering of light by hot polaritons. This work was supported by the Italian Consiglio Nazionale delle Ricerche del Ministero della Pubblica Istruzione.     

A simple method for the optogalvanic detection of argon ion transitions in hollow-cathode lamps

Summary We describe a simple method for the observation of argon ion transitions in hollow-cathode lamps, using the optogalvanic effect, and report the first optogalvanic detection of the six ArII transitions: 457.9 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm and 514.5 nm. We also study the optogalvanic signal as a function of the incident laser power and the lamp current. Partial financial support of CNPq and FINEP (Brazil).     

Electrolyte interaction with DPPC vesicles: An ESR study

Summary The partition of the spin probe TEMPO between the fluid lipid phase of single-walled vesicles of dipalmitoylphosphatidylcholine and the aqueous bulk solution have been used to investigate the interaction of monovalent ions with polar head of neutral phospholipids. The study has been performed by electron spin resonance (ESR) spectroscopy in the temperature range of (20÷60)°C and in the presence of (0÷3) M 1∶1 electrolyte. In the absence of electrolyte the spin probe TEMPO reveals the characteristic order→disorder DPPC main phase transition atT _m≈37°C, while the pretransition occurs atT _p≈27.5°C. On increasing the ionic strength of the dispersion medium it results for the partition coefficient,P _C, that, at each temperature,P _C(3)>P _C(2)>P _C(1)>P _C(0). Correspondingly, the pretransition disappears and theT _m value downshifts from ≈37°C with 0 M electrolyte to ≈34°C with 3M salt in the order:T _m(3)>T _m(2)>T _m(1)>T _m(0). The results suggest an increase in the net surface charge density of vesicles due to high ionic-strength values. The alteration of the electric interactions occurring into the polar zone of DPPC bilayer reduces the hindrances which, in turn, favour the enhancement of TEMPO partitioning in the hydrophobic core of phospholipid bilayers. The authors of this paper have agreed to not receive the proofs for correction.     

Raman scattering by hot polaritons in NaClO3

Summary By nonlinear mixing of IR and visible radiation,i.e. coherent Raman scattering by polaritons driven by a CO₂ laser, it has been possible to get high-resolution spectra for theF-modes of a NaClO₃ crystal in the region (907÷957) cm⁻¹, where several isotopic modes are present. The obtained independent measurement of the refractive index and absorbance allows an accurate determination of the polariton dispersion curve and its width inq-space. The experimental data confirm the existence of a localized isotopic mode at 931 cm⁻¹ and a strongly damped isotopic mode near 960 cm⁻¹. Finally, an accurate measurement of the dispersion of the second-order nonlinear polarizability in the same energy region has been obtained for the first time. This work was supported by the Italian Consiglio Nazionale delle Ricerche and Ministero della Pubblica Istruzione.     

Inhomogeneous broadening effects in high-gain free electron laser operation: A simple parametrization

Summary In this paper we present a simple parametrization of the effects of gain degradation induced in high-current FELs by the inhomogeneous broadenings due to the energy spread and emittances of the electron beam. The parametrization is based on a fitting procedure of the numerical data. The accuracy of the fit is better than 1%.

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Riassunto In questo lavoro si analizzano gli effetti di allargamento inomogeneo in FEL operanti nel regime di alto guadagno. Si presenta una semplice formula che permette di parametrizzare il guadagno in funzione dei parametri inomogenei dovuti allo spread di energia ed alle emittanze. La parametrizzazione è basata su una procedura di interpolazione dei dati numerici. L'accuratezza della interpolazione è migliore dell'1%.

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Резюме В этой работе анлизируется влияние эффектов неоднородного уширения на действие лазера на свободных электронах с высоким усилением. Предлагается простая формула для параметризации коэффициента усиления в зависимости от параметров неоднородного уширения, связанных с разбросом энергии и эмиттанса электронного пучка. Параметризация основана на интерполяции численных данных. Точность интерполяции оказывается лучше 1%.

     

Effect of the incoherent emission on the FEL pulse width

Summary In this paper we discuss the effect of the incoherent spontaneous emission on the FEL pulse width. We analyse the dependence of the laser spatial width on the number of round trips, within the framework of the supermodes’ theory. We also study the distortion induced in the supermode spectrum by the incoherent emission.

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Riassunto Gli autori discutono l’effetto della emissione spontanea incoerente sull’ampiezza dell’impulso laser in un FEL nel corso dell’evoluzione del segnale. Le espressioni riportate sono derivate nel contesto della teoria dei supermodi precedentemente sviluppata relativamente al regime di basso guadagno e piccolo segnale e nell’ipotesi di pacchetto di elettroni lungo.

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Резюме В этой статье мы обсуждаем влияние некогерентного спонтанного нзлучения на ширину импульса в лазере на свободных электронах. Мы анализируем зависимость пространственной ширины импульса лазера от числа пролетов в рамках теории супер-мод. Мы также исследуем дисторсию, индуцированную в спектре супермод из-за некогерентного излучения.

     

Raman spectroscopy in GaS: Zone boundary phonon interactions

Summary A complete polarization analysis of the GaS Raman spectrum, for excitation energies below the indirect energy gap, is reported. In order to assign second-order combinations and defect-induced forbidden modes, that appear in the spectra besides the six well-known Γ-phonons, also IR transmittance and reflectance measurements, for bothE⊥c andE‖c, have been performed. All the available selection rules are applied to both Raman and IR data, allowing to identify the high-symmetry points of phonons involved in the scattering and, when possible, to ascribe the main non-Γ structures of the spectra to the knownK andM point modes. This analysis brings to several new attributions, also ruling out some previous assignments, based on the separate study of either Raman or IR spectra. Work partially supported by M.P.I.     

Dispersed lyotropic phases as carriers for active substances

Summary Smectic mesophases of water-insoluble compounds can be dispersed to form multilayered structures (liposomes). These provide different siters for the solubilization or entrapment of active compounds such as drugs. The specific advantages and drawbacks of these systems are discussed in comparison with those of other carriers for what concerns the aspects of feasibility, versability, encapsulating ratio, shelf life and fatein vivo. The tendency of liposomes to be taken up by particular cells can be exploited in passive targeting. Much effort is devoted now to active targeting of these particles by gearing them with specific ligands. This is still a far cry from the applications of lyotropics in systemic therapy. Topical administration of vesicles offers several advantages which have been identified in the field of skin care products. Experimental data are provided to substantiate this view. Finally it is worthwhile mentioning that vesicles of adequate chemical composition are stable in oil-amphiphile-water systems. This fact raises theoretical questions and at the same time opens new avenues to the development of multicompartment carriers. Paper presented at the ?Meeting on Lyotropics and Related Fields?, held in Rende, Cosenza, September 13–18, 1982.     

Preparation and Raman spectroscopy of Zn x Cd1−x In2S4 mixed cation layered compounds

Summary We report on the growth and the structural and dynamical analysis of the layered phases which are formed in Zn _x Cd_1−x In₂S₄ quaternary mixed compounds. The experiments show that two polytypic phases are formed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Structural properties of aqueous electrolyte solutions from i.r. absorption spectra

Summary Results are reported on near-i.r. absorption spectra of H₂O in the presence of a variety of electrolytes, in the temperature range of liquid state. Spectra are analysed by using a deconvolution method, presented and discussed in previous works, thus obtaining a new level of detail and completeness of information. This allows for the first time the separation of solute perturbation on the solvent structure in terms of electric-field effects (common to all solutes), steric effects (mainly determined by the ionic radius) and more subtle effects due to the electronic structure of the specific ion. The quantitative set of spectroscopical parameters obtained for the different solutions in the whole explored temperature range offers a potentially useful ground for comparison with results of computer simulation.

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Riassunto In questo lavoro sono riportati risultati sugli spettri di assorbimento di H₂O nel vicino infrarosso in presenza di una varietà di elettroliti, nell'intervallo di temperatura dello stato liquido. Gli spettri sono analizzati usando un metodo di deconvoluzione, presentato e discusso in precedenti lavori, ottenendone un nuovo grado di risoluzione e completezza d'informazione. Questo ha permesso per la prima volta la separazione della perturbazione indotta dai soluti sulla struttura del solvente in termini di effetti di campo elettrico (comune a tutti gli ioni), effetti sterici (in media dipendenti dai raggi ionici) ed effetti piú fini dovuti alla struttura elettronica dei singoli ioni. Il quadro quantitativo dei parametri spettroscopici ottenuti per le differenti soluzioni nell'intervallo di temperature esplorato offre una base potenzialmente utile per un confronto con i risultati di simulazione al computer.

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Резюме Приводятся результаты для слектров инфракрасного поглошения H₂O в присутствии различных электролитов в области температуп жидкого состояния. Полученные спектры анализируются, используя метод ?развертывания?, предложенный в предыдуших работах с целью получения нового уровня полноты информации. Этот подход впервые позволил разделить возмушение, обусловленное растворенным вешеством на структуру растворителя, на эффекты электрического поля (обшие для всех растворенных вешеств), на сферические эффекты (зависяшие от радиуса иона) и на более тонкие эффекты, обусловленные электронной структурой отдельного иона. Количественная система спектроскопических параметров, полученных для различных растворов во всей исследованной области температур, представляет потенциально полезную основу для сравнения с результатами машинного моделирования.

     

Raman spectra of CuGaS2-x Se x (x=0, 0.5, 1.0)

Summary Raman spectra on the CuGaS_2-x Se _x system (x=0, 0.5, 1.0) are described for the first time. The observed structures are assigned on the basis of the analogies with binary solid solutions. The broadening of theA ₁ sulphur mode seems to indicate the effect of substitutional disorder. Paper presented at the ?V. International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Anomalies in the polarized raman spectrum of crystal quartz

Summary By means of coherent Raman scattering we have measured in quartz the dispersion of the elements of the Raman tensor in the range (900÷1070) cm⁻¹. The results determine with good accuracy the relative contribution of the various modes to the second-order nonlinear susceptibility. For some elements of the Raman tensor the present results greatly improve the precision of data already known; for others the dispersion and the relative strengths have been measured for the first time. In particular, a strong, frequency-dependent, asymmetry of the Raman tensor has been evidentiated; this asymmetry is interpreted in terms of optical Raman activity.