Active laser frequency stabilization using neutral praseodymium (Pr)

We present a new possibility for the active frequency stabilization of a laser using transitions in neutral praseodymium. Because of its five outer electrons, this element shows a high density of energy levels leading to an extremely line-rich excitation spectrum with more than 25000 known spectral lines ranging from the UV to the infrared. We demonstrate the active frequency stabilization of a diode laser on several praseodymium lines between 1105 and 1123 nm. The excitation signals were recorded in a hollow cathode lamp and observed via laser-induced fluorescence. These signals are strong enough to lock the diode laser onto most of the lines by using standard laser locking techniques. In this way, the frequency drifts of the unlocked laser of more than 30 MHz/h were eliminated and the laser frequency stabilized to within 1.4(1) MHz for averaging times >0.2 s. Frequency quadrupling the stabilized diode laser can produce frequency-stable UV-light in the range from 276 to 281 nm. In particular, using a strong hyperfine component of the praseodymium excitation line E = 16 502.616_7/2 cm^-1 -> E' = 25 442.742_9/2 cm^-1 at lambda = 1118.5397(4) nm makes it possible - after frequency quadruplication - to produce laser radiation at lambda/4 = 279.6349(1) nm, which can be used to excite the D2 line in Mg^+.Comment: 10 pages, 14 figure

Formation of Galactic Systems in Light of the Magnesium Abundance in Field Stars: The Thick Disk

The space velocities and Galactic orbital elements of stars calculated from the currently available high-accuracy observations in our summary catalog of spectroscopic magnesium abundances in dwarfs and subgiants in the solar neighborhood are used to identify thick-disk objects. The relative magnesium abundances in thick-disk stars are shown to lie within the range 0.0<[Mg/Fe]<0.5 and to decrease with increasing metallicity starting from [Fe/H]=-1.0. This is interpreted as evidence for a longer duration of the star formation process in the thick disk. We have found vertical gradients in metallicity (grad_Z[Fe/H]=-0.13\pm 0.04 kpc^{-1}) and relative magnesium abundance (grad_Z [Mg/Fe]=0.06\pm 0.02 kpc^{-1}), which can be present in the subsystem only in the case of its formation in a slowly collapsing protogalaxy. The large spread in relative magnesium abundance (-0.3<[Mg/Fe]<0.5) in the stars of the metal-poor "tail" of the thick disk which constitute 8% of the subsystem, can be explained in terms of their formation inside isolated interstellar clouds that interacted weakly with the matter of a single protogalactic cloud. We have found a statistically significant negative radial gradient in relative magnesium abundance in the thick disk (grad_R [Mg/Fe]=-0.03\pm 0.01 kpc^{-1}) instead of the expected positive gradient. The smaller perigalactic orbital radii and the higher eccentricities for magnesium-richer stars, which among other stars, are currently located in a small volume of the Galactic space near the Sun are assumed to be responsible for the gradient inversion. A similar but statistically less significant inversion is also observed in the subsystem for the radial metallicity gradient.Comment: Accepted for 2005, Astronomy Letters, Vol. 31, No. 8, P.515-527; 14 pages, 6 figure

Stars of extragalactic origin in the solar neighborhood

We computed the spatial velocities and the galactic orbital elements using Hipparcos data for 77 nearest main-sequence F-G-stars with published the iron, magnesium, and europium abundances determined from high dispersion spectra and with the ages estimated from theoretical isochrones. A comparison with the orbital elements of the globular clusters that are known was accreted by our Galaxy in the past reveals stars of extragalactic origin. We show that the relative elemental abundance ratios of r- and \alpha- elements in all the accreted stars differ sharply from those in the stars that are genetically associated with the Galaxy. According to current theoretical models, europium is produced mainly in low mass Type II supernovae (SNe II), while magnesium is synthesized in larger amounts in high mass SN II progenitors. Since all the old accreted stars of our sample exhibit a significant Eu overabundance relative to Mg, we conclude that the maximum masses of the SNII progenitors outside the Galaxy were much lower than those inside it are. On the other hand, only a small number of young accreted stars exhibit low negative ratios $[Eu/Mg] < 0$. The delay of primordial star formation burst and the explosions of high mass SNe II in a relatively small part of extragalactic space can explain this situation. We provide evidence that the interstellar medium was weakly mixed at the early evolutionary stages of the Galaxy formed from a single proto-galactic cloud and that the maximum mass of the SN II progenitors increased in it with time simultaneously with the increase in mean metallicity.Comment: Accepted for 2004, Astronomy Letters, Vol. 30, No. 3, P.148-158 15 pages, 3 figure

Localization of Acoustic Signals Used in Sound Emitters at Pedestrian Crosswalks

This study aimed at determining an optimal acoustic signal, which could be used in sound emitters at blind and visually impaired enabled pedestrian crosswalks. Two signals were identified from among groups of tested signals on the basis of psychoacoustic tests. These two signals met the following standard requirements: TR signal - a signal with a triangular temporal envelope and a sinusoidal carrier and RC signal - a signal with a rectangular temporal envelope and a rectangular carrier, both with a basic frequency of 880 Hz, repeated periodically with a frequency of 5 Hz. The ability to localize was tested by a modified method of angle of directional hearing acuity in which the two alternative forced choice adaptation procedure was used. The test signals were emitted against the background of traffic noise and the ratio of the useful signal (65 dB SPL) to noise (75 dB SPL) was (-10 dB). The tests were conducted on 8 subjects with normal hearing (5 women and 3 men), aged 22-37 years. Following statistical analysis it was found that: individual subjects' responses differed considerably with respect to angle of direction hearing acuity values, localization is most difficult at the angles of 90° and 270°, worse localization for trams noise were stated, RC signals are better localized than TR signals

Psychoacoustical Estimation of Selected Acoustic Signals Which Can Be Applied at Pedestrian Crosswalks

The paper presents a psychoacoustical evaluation of selected acoustic signals, which according to Polish and international recommendations can be applied at pedestrian crosswalks. The aim of the study was the optimal adjustment of parameters of the signals emitted at pedestrian crosswalks, and to meet the expectations of persons with vision impairments as well as nearby residents or workers working near the crossing. The psychoacoustical evaluation of acoustic signals consists of determination of the hearing threshold of signals in the quiet, detection of signals presented against a background of various types of traffic noises (estimated signal-to-noise ratio) and annoyance assessment of signals. Three types of intermittent sounds were analysed: signals with rectangular time pattern filled up with rectangular wave, signals with rectangular time pattern filled up with sinusoidal wave and signals with triangular time pattern filled up with sinusoidal wave. Four fundamental frequencies (550 Hz, 880 Hz, 1580 Hz and 2000 Hz) and two repetition rates (5 Hz and 9 Hz) were tested. The results of the study have shown that the most suitable signals which can be applied at pedestrian crosswalks are the intermittent sounds with rectangular time pattern filled up with rectangular wave of fundamental frequencies 880 Hz and 1580 Hz and repetition rate 5 Hz and the intermittent sounds with rectangular time pattern and triangular time pattern both filled up with sinusoidal wave of fundamental frequencies 1580 Hz and repetition rate 5 Hz

Localization of Acoustic Signals Used in Sound Emitters at Pedestrian Crosswalks

This study aimed at determining an optimal acoustic signal, which could be used in sound emitters at blind and visually impaired enabled pedestrian crosswalks. Two signals were identified from among groups of tested signals on the basis of psychoacoustic tests. These two signals met the following standard requirements: TR signal - a signal with a triangular temporal envelope and a sinusoidal carrier and RC signal - a signal with a rectangular temporal envelope and a rectangular carrier, both with a basic frequency of 880 Hz, repeated periodically with a frequency of 5 Hz. The ability to localize was tested by a modified method of angle of directional hearing acuity in which the two alternative forced choice adaptation procedure was used. The test signals were emitted against the background of traffic noise and the ratio of the useful signal (65 dB SPL) to noise (75 dB SPL) was (-10 dB). The tests were conducted on 8 subjects with normal hearing (5 women and 3 men), aged 22-37 years. Following statistical analysis it was found that: individual subjects' responses differed considerably with respect to angle of direction hearing acuity values, localization is most difficult at the angles of 90° and 270°, worse localization for trams noise were stated, RC signals are better localized than TR signals

The Concept of the Auditory Training for Blind and Visually Impaired Children and Teenagers

The paper was inspired by the hitherto published results concerning provision of efficient assistance to visually impaired persons by means of acoustic and vibratory signals. The aim of the auditory training is to shorten the time necessary for execution of auditory information processing, sensibilize blind persons to differences in sounds and teach them to focus auditory attention on small differences in parameters of acoustic waves, in order to achieve independent and correct interpretation of environment by hearing and listening. The basic concept of the auditory training addressed to blind or visually impaired children and teenagers is presented in detail. Preliminary verification of the effectiveness of training of young adults without vision impairments has not shown statistically significant differences in performance before and after the training. Possible reasons for such an effect are pointed out and solutions are suggested

Studies of Hyperfine Structure of LaI by Laser Spectroscopy on Atomic Beam

High-resolution Doppler-reduced laser spectroscopic investigations on an atomic beam of $\text{}^{139}$La were carried out to study hyperfine structure of 8 odd levels. The magnetic-dipole coupling constants A and the electric-quadrupole coupling constants B were determined and compared with the data from literature, if available