Dehydrogenation study of cosmic-dust analogue grains

Summary New infrared and optical-absorption measurements performed on hydrogenated amorphous-carbon grains are presented. In particular, the spectral modifications produced by dehydrogenation of the samples are analysed. We interpret the observed variations in terms of an increasing dimension of the graphitic clusters disordely arranged to form carbon grains. The results support the hypothesis that the behaviour of the interstellar extinction in the ultraviolet can be attributed to dehydrogenated amorphous-carbon grains. Paper presented a the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

An estimate of the secondary-proton spectrum at small atmospheric depths

Summary We have calculated the energy spectrum of secondary protons produced in the atmosphere as a function of the atmospheric depth and zenith angles at a location with zero geomagnetic cut-off. In this calculation, we have included all relevant energy losses and production processes. It is shown that the protons produced from the target nuclei through recoil and evaporation processes dominate the spectrum below 350 MeV. These calculations have been carried out over an energy region from 20 MeV to 40 GeV and up to a depth of 40 g/cm² of the atmosphere over a latitude with zero geomagnetic cut-off for both the periods of minimum and maximum solar modulation.     

Experimental determination of scattering matrices of dust particles at visible wavelengths: The IAA light scattering apparatus

We present a new apparatus for measuring the complete scattering matrix as a function of the scattering angle of dust irregular particles. The design is based on the well-known apparatus located in Amsterdam, The Netherlands. In this improved version we have extended the scattering angle ranging from 3° to 177°. Moreover, the measurements are performed with a tunable argon–krypton laser that emit at a wavelength (λ) of 483, 488, 520, 568, or 647 nm. The apparatus has been developed at the Instituto de Astrofísica de Andalucía (IAA), Granada, Spain. To measure the scattering matrix elements we use a number of different optical components such as polarizers, a quarter-wave plate, and an electro-optic modulator. These components are used to manipulate the polarization state of light. By using eight different combinations for the orientation angles of the optical components, all scattering matrix elements are obtained as functions of the scattering angle. The accuracy of the instrument is tested by comparing the measured scattering matrices of water droplets at 488, 520, and 647 nm with Lorenz–Mie calculations for a distribution of homogeneous water droplets.     

An analysis of pulsar timing irregularities: is it induced by a source of gravitational waves in the galaxy?

Summary A statistical analysis of the irregularities in the pulse arrival times for the some 30 pulsars, for which the timing noise measurements are available, indicates that, at a confidence level of 96%, the timing noise is induced by a hypothetical source within our Galaxy. The source would be located at 08 h 38 min right ascension, −3° declination and 0.9 kpc distance from the solar system. We suggest and discuss the possibility that the interaction between the ?source? and the pulsars is due to gravitational waves, emitted in bursts by the hypothetical source with yearly rate over the past 10⁵ years. Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983.     

Condensation of cosmic analog material in microgravity conditions: Preliminary analysis of a first set of flights

Summary In this paper we give a brief summary of the first results obtained in the frame of the STARDUST project. The aim of the experiment is to simulate the condensation of cosmic-dust analog materials under microgravity conditions. This approach will allow to reproduce actual condensation processes active in space better than in the laboratory experiments performed so far. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Derivation of muon spectrum at high energies from the recent JACEE primary cosmic-ray spectrum using Fermilab data on meson production

Summary The energy spectrum of sea level muons in the range (10²÷10⁴) GeV has been calculated from the latest directly measured JACEE primary spectrum using Fermilab results on pp→π^± X and pp→K^± X inclusive reactions. The conventional pion atmospheric diffusion equation after Bugaevet al. has been used in this analysis to account the flux of muons emerged from the multiple generation of mesons in air. The derived muon spectrum has been compared with the earlier magnetic spectrograph data of Durham and Kiel groups. The latest BAKSAN scintillator telescope data is well in agreement with the calculated integral spectrum originated from the meson decays in the range (1÷10⁴) GeV.     

Dust in the planetary system: Dust interactions in space plasmas of the solar system

Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust–plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust.     

An investigation into the sensitivity of various albedo neutron dosimeters aimed at correcting the readings

The results of an experimental determination of the sensitivity of three types of individual neutron albedo dosimeters in neutron reference fields on the basis of radionuclide sources and at the top concrete shielding of the U-70 accelerator are presented. The results show that the ratios between the responses of the albedo dosimeters designed earlier at the Joint Institute for Nuclear Research (the albedo dosimeter (AD) and the multicomponent dosimeter (MD)) and the currently used DVGN-01 dosimeter are constant within 25% in a wide range of neutron energy. This fact makes it possible to use the results of measuring the AD and MD responses obtained earlier in neutron fields of nuclear-physical installations at the Joint Institute for Nuclear Research (JINR) for the correction of DVGN-01 dosimeter measurement results to apply it to personal radiation monitoring (PRM) at these installations. The correction factors for DVGN-01 measurement results are found and recommended to be used in PRM for most JINR installations.     

On the biological effects of cosmic rays: Epidemiological studies

Summary Determining the biological effects of cosmic rays and other natural ionizing radiations, could possibly help us in shedding light on the more general problem of low-dose ionizing-radiation effects. In this work we provide a survey of the most recent studies available on epidemiological methods: we discuss the main difficulties in using these methods, as well as the discrepancies in their results. Work presented as a poster at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Primary cosmic-ray composition in the energy range of 1014 eV to 1016 eV and high-energy atmospheric cosmic rays observed with emulsion chambers at Mt. Kanbala

Summary We report on the results of the measurements of energy spectra of atmospheric cosmic rays in the energy around 10 TeV measured with emulsion chambers at Mt. Kanbala (5500 m above sea-level, atmospheric depth 520 g/cm²). The power indices of the integral spectra take the values of 2.00±0.08 for gamma-rays and 1.90±0.10 for hadrons, in the energy range from 5 TeV to 20 TeV. Their intensities are compatible with those expected from the primary cosmic rays containing fewer protons than in the lower energy region. The energy spectrum of family events is also discussed with reference to the composition of primary cosmic rays. It is concluded that the portion of protons in the primary cosmic rays gradually decreases in the energy range from 10¹³ eV to 10¹⁵ eV.

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Riassunto Si riportano i risultati delle misurazioni degli spetri di energia dei raggi cosmici atmosferici all'energia di circa 10 TeV misurata con camere d'emulsione a Mt. Kambala (5500 m sul livello del mare, profondità atmosferica 520 g/cm²). Gli indici di potenza degli spettri integrali assumono i valori di 2.00±0.08 per i raggi gamma e 1.90±0.10 per gli adroni, nell'intervallo di energia da 5 TeV a 20 TeV. Le loro intensità sono compatibili con quelle attese dai raggi cosmici primari che contengono meno protoni che nella regione d'energia inferiore. Lo spettro d'energia degli eventi della famiglia è discusso anche con riferimento alla composizione dei raggi cosmici primari. Si conclude che la porzione di protoni nei raggi cosmici primari diminuisce nell'intervallo d'energia da 10¹³ eV a 10¹⁵ eV.

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Резюме Мы приводим результаты измерений энергетических спектров атмосферных космических лучей при энергиях порядка 10 TeB, определенных с помощью змульсионных камер на г. Канбала (5500 м выше уровня моря, атмосферная глубина 520 r/cm²). Степенные показатели интегральных спектров имейт значения 2.00±0.08 для гамма-лучей и 1.90±0.10 для адронов, в области энергий от 5 ТэВ до 20 ТэВ. Полученные интенсивности оказывайтся совместимыми с ожидаемыми интенсивностями от первичных космических лучей, содержащих меньшее число протонов, чем в области меньших энергий. Также обсуждается энергетнческих спектр семейства событий относительно соства первичных космических лучей. Утверждается, что доля протонов в первичных космических лучах постепенно уменьшается в области энергий от 10¹³ зВ до 10¹⁵ эВ.

     

An experimental study on the characterization of electric charge in electrostatic dust removal

Automatic dust removal using the electrostatic forces of electrodynamic screen (EDS) is an emerging method for mitigation of energy yield losses caused by dust accumulation on solar collectors. Both electric field distribution and dust particles' charge acquired during the removal process play pivotal roles in thorough evaluation of EDS performance. Previous studies have comprehensively analyzed the electric field distribution in EDS. In this paper we have conducted a number of experiments to examine how two EDS design parameters, electrode width and inter-electrode spacing, and two operational parameters, applied voltage and relative humidity, affect dust particles' charge. Sixteen EDS prototypes in two sets were developed and tested in a laboratory environment to study the acquired charge by dust particles via charge-to-mass ratio measurements. It has been shown that the charge-to-mass ratio is directly affected by the electric field intensity on an EDS surface. Furthermore, we have shown the detrimental impact of relative humidity on EDS performance. The results are advantageous in the evaluation of EDS design and its optimization to attain maximum dust removal efficiency.     

Short-period variation of cosmic-ray intensity observed in the stratosphere

Summary To investigate the variation of the cosmic-ray intensity in the Earth atmosphere, stratospheric balloon soundings are performed weekly at Campinas (Brazil). During the flight of May 20th, 1988 short-period variations were detected. Through Fourier analysis it was identified a period of ∼2.5 min, with a confidence level of 99.6% between 23 g/cm² and 173 g/cm². Apparently these oscillations are not correlated either with the earth magnetic field or solar activity, suggesting their atmospheric origin, nevertheless it is difficult to explain the production mechanisms of these disturbances.

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Riassunto Per studiare le variazioni dell'intensità dei raggi cosmici nell'atmosfera terrestre sono messi in funzione palloni sonda stratosferici settimanalmente a Campinas (Brasile). Durante il volo del 20 Maggio 1988 sono state registrate variazioni a breve periodo. Mediante l'analisi di Fourier è stato identificato un periodo di ≈2.5 min con un livello di confidenza di 99.6% tra 23 g/cm² e 173 g/cm². Apparentemente queste oscillazioni non sono correlate né con il campo magnetico terrestre né con l'attività solare, il che suggerisce la loro origine atmosferica, nonostante sia difficile spiegare i meccanismi di produzione di queste perturbazioni.

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Резюме для исследования изменения интенсивности комсических лучей в земной атмосфере еженелельно запускайтся стратосферные шарызонды в лаборатории Кампинас (Бразилия). Во время подыта 20 мая 1988 года, были зарегистрированы изменения с коротким периодом. С помощью фурье-анализа определен период 2.5 минуты, с уровнем достоверности 99.6%, в области между 23 г/см² и 173 г/см². По-видимому, эти осцилляции не связаны ни с магнитным полем Земли, ни с солнечной активностью. Предполагается их атмосферное происхождение, тем не менее трудно обБяснить механизм образования этих возмущений.

     

An experimental study of the production of neutral pions in p̄p annihilations at 1.6 GeV/c

The heavy liquid bubble chamber Garamelle has been used to study the rate of production of neutral pions in the pionic annihilation of 1.6 GeV/c antiprotons on free protons. Preliminary results are presented on the relative cross-sections for most channels together with the mean π⁰ multiplicity and the first moments for annihilation into 0-prongs, 2-prongs, 4-prongs and 6-prongs.     

An experimental limit on production of axions in a fission reactor

We report on an experiment conducted at the ILL reactor aimed at searching for coincident gamma-ray events from axion decay. No such events are seen and our results are interpreted, using the calculations by Donnelly et al., as an upper limit of the axion mass of 280 keV.     

Simple leaky box model for cosmic-ray propagation, models for production of antiprotons at ultrahigh energies and the estimations of the [`(p)]/p\bar p/p ratiosratios

Summary Accepting the simple leaky box model as the basis for propagation of cosmic rays, the problematical ratio has been estimated theoretically by applying two versions of antiproton production models. The results have been compared with those from the experiments as well as from some other empirio-theoretical models. It has been emphatically pointed out that even within the premises of the simple leaky box model the discrepancies can be removed only by taking into account the contributions from the large-p _T antiproton production cross-sections and the role of theA-dependence of nuclear cross-sections in a much more pronounced way.

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Riassunto Accettando il modello semplice della scatola non isolata, è stato stimato il rapporto critico teoricamente applicando due versioni dei modelli di produzione degli antiprotoni. Sono stati confrontati i risultati con quelli degli esperimenti ed anche con quelli di altri modelli empirico-teorici. è stato evidenziato che anche nell’ambito delle premesse del modello semplice della scatola non isolata si possono eliminare le discrepanze tenendo maggiormente conto dei contributi delle sezioni d’urto di produzione di antiprotoni a grandep _T e del ruolo della dipendenza daA delle sezioni d’urto nucleare in modo molto più marcato.

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Простая модель распространения космических лучей, модели образования антипротонов при ультравысоких Энергиях и оценки отнощенийотнощений

Резюме Ha основе простой модели распространения космических лучей теоретически оценивается отнощение, используя две модели образования антипротонов. Полученные результаты сравниваются с результатами Экспериментов, а также с результатами других Эмпирико-теоретич еских моделей. Отмечается, что, используя только предположения простой модели, можно устранить расхождения, если учесть вклады поперечных сечений образования антипротонов с больщимир _T и более явно зависимость от А ядерных поперечных сечений.

     

An experimental determination of the critical exponents at the metal-insulator transition

This work deals with a determination of the magnitude of the critical exponents and their ratio from an analysis of the temperature dependence of the conductivity and magnetoresistivity of doped Ge 〈 As 〉 with an impurity concentration making it an insulator near the metal-insulator transition. The values found are $\text{?? = 0.60 ± 0.04}$, ξ = 1.38 ± 0.07, $\text{ξ}\text{??}\text{= 2.3 ± 0.2}$; neither the critical exponents nor their ratio depend on compensation within 0 < k < 60%.     

An experimental investigation on mixing enhancements in non-circular sharp-edged nozzles using the entropy production concept

An experimental study on mixing enhancement in free jets, issuing from sharp-edged nozzles of different geometry, is performed by using particle image velocimetry. The attention is focused on the jet near-field and interaction zones (0 < X/D < 18, where X is the axial coordinate and D the diameter of the equivalent circular jet). The mixing efficiency is evaluated and quantified using the definition of entropy production derived from the velocity field. The effect of Reynolds number is also discussed by performing measurements at Re = 8000 and Re = 35,000. The results are compared to circular nozzle data to evaluate the change in mixing efficiency among axisymmetric and non-symmetric nozzles. While the effect of Reynolds number on mixing is small, at least for the values tested here, the change in geometry is rather crucial. In terms of entropy production, the rectangular and elliptical nozzles show higher mixing for X/D< 7, whereas the other ones attain the best results for larger distances. This behaviour is basically related to the axis-switching phenomenon observed in elongated jets. Different variables are tested and compared as possible velocity and length scales to derive a meaningful non-dimensional entropy production.