An Empirical Titrimetric Method for the Determination of Beryllium

Recently, in connection with a study of the metallurgy of beryllium, a rapid and accurate method was needed for the determination of this metal. A review of the literature revealed that the existing titrimetric methods are based on hydrolysis, neutralization or precipitation reactions. These methods are outlined briefly below. 1. Direct titration of a beryllium salt with sodium hydroxide using phenolphthalein as the indicator (3). 2. An iodometric titration of the acid resulting from the hydrolysis of a beryllium salt (3, 10). 3. Hydrolysis of a fluoberyllate in the presence of calcium chloride followed by titration with sodium hydroxide using phenolphthalein as the indicator (4, 17). 4. Hydrolysis of a fluoberyllate in the presence of calcium chloride followed by an iodometric titration of the resulting acid (11). 5. Precipitation of beryllium hydroxide followed by dissolution in excess hydrochloric acid and the iodometric determination of the excess acid (7). 6. Precipitation of small amounts of beryllium by titration with a standard quinalizarin solution (8, 9). 7. Potentiometric titration of beryllium solutions with standard sodium fluoride solution (16). 8. Titration of beryllium solutions with sodium hydroxide, ammonium hydroxide or triammonium phosphate. The progress of the titration is followed by means of a high frequency titrimeter (13)

Zinc - 1,10-phenanthroline complexes and their analytical application

The use of ultraviolet spectrophotometry for quantitative inorganic analytical purposes has long remained unexploited. An extremely large number of complexes of metals have characteristic absorption properties in the visible portion of the spectrum and many colorimetric methods of analysis depend upon this fact. With the present availability of ultraviolet spectrophotometric equipment the charachteristic absorption properties of many colorless metallic complexes in the ultraviolet region of the spectrum should as conveniently be capable of similar utilization

¿Podem as estruturas escolares melhorar as relações entre alunos e professores? A relação entre os períodos de orientação, atenção individualizada e o desempenho acadêmico dos estudantes

In this paper, we present findings from a three-year study of students' perceptions of personalization and, specifically, advisory as a reform strategy and its relationship to students' academic progress at 14 recently converted small high schools in a large, urban school district in California. This study examined the degree to which students' sense of personalization (connections to the school and to adults at the school) interacted with students' academic achievement, as measured by standardized test scores and weighted grade-point averages. In particular, we examined the relationship between students' perceptions of formal structures to enhance personalization -- such as advisory periods -- and students' academic achievement.Este estudio se centr en las relaciones entre las percepciones de estudiantes sobre niveles de personalizacin, sus opiniones sobre los periodos de asesoramiento, y los resultados acadmicos. Durante tres aos consecutivos se administraron 10.044 encuestas a estudiantes en 14 escuelas pequeas y re-estructuradas. Las respuestas fueron vinculadas a los promedios generales de las notas de los estudiantes ponderadas durante un solo ao y a los resultados de las pruebas normalizadas en Artes del Lenguaje Ingls. Los resultados de una serie de modelos de niveles mltiples indicaron que las percepciones ms positivas sobre la personalizacin pronosticaron mejores resultados acadmicos. Las percepciones de los estudiantes sobre el perodo de asesoramiento tambin fueron relacionados con el logro acadmico, pero en direccin opuesta: sentimientos positivos acerca de los perodos de asesoramiento se asociaron con peores resultados acadmicos. Estos resultados son consistentes con un trabajo cualitativo que sugiere que niveles ms altos de personalizacin son asociados con niveles ms altos de logros acadmicos, mejoras en la cultura escolar y ms compromiso de los estudiantes. Sin embargo, estos resultados tambin sugieren que las relaciones entre perodos de asesoramiento, personalizacin y resultados acadmicos no son tan sencillas como se haba pensado anteriormente.Este estudo focalizou as relaes entre as percepes dos alunos sobre os nveis de ateno individualizada e suas opinies sobre os perodos de orientao, com resultados acadmicos. Por trs anos consecutivos foram administrados 10.044 questionrios a alunos em 14 pequenas escolas que passaram for reformas. As respostas foram relacionadas com as mdias globais das notas dos alunos durante um nico ano ponderado e os resultados de testes padronizados na disciplina Lngua Inglesa. Os resultados de uma srie de modelos multi-nvel indicaram que as percepes mais positivas sobre a ateno individualizada prognosticaram melhores resultados acadmicos. As percepes dos alunos sobre o perodo de orientao tambm foram relacionadas com os resultados acadmicos, mas na direo oposta: sentimentos positivos sobre os perodos de orientao foram associados com piores resultados acadmicos. Estes resultados coincidem com um trabalho qualitativo que sugere que nveis mais elevados de ateno individualizada esto associados com nveis mais elevados de rendimento acadmico, melhorias na cultura escolar e mais engajamento dos alunos. No entanto, esses resultados tambm sugerem que as relaes entre perodos de orientao, ateno individualizada e os resultados acadmicos no so to simples quanto se pensava anteriormente

Fitting Together the HI Absorption and Emission in the SGPS

In this paper we study 21-cm absorption spectra and the corresponding emission spectra toward bright continuum sources in the test region (326deg< l < 333 deg) of the Southern Galactic Plane Survey. This survey combines the high resolution of the Australia Telescope Compact Array with the full brightness temperature information of the Parkes single dish telescope. In particular, we focus on the abundance and temperature of the cool atomic clouds in the inner galaxy. The resulting mean opacity of the HI, , is measured as a function of Galactic radius; it increases going in from the solar circle, to a peak in the molecular ring of about four times its local value. This suggests that the cool phase is more abundant there, and colder, than it is locally. The distribution of cool phase temperatures is derived in three different ways. The naive, ``spin temperature'' technique overestimates the cloud temperatures, as expected. Using two alternative approaches we get good agreement on a histogram of the cloud temperatures, T(cool), corrected for blending with warm phase gas. The median temperature is about 65 K, but there is a long tail reaching down to temperatures below 20 K. Clouds with temperatures below 40 K are common, though not as common as warmer clouds (40 to 100 K). Using these results we discuss two related quantities, the peak brightness temperature seen in emission surveys, and the incidence of clouds seen in HI self-absorption. Both phenomena match what would be expected based on our measurements of and T(cool).Comment: 50 pages, 20 figure

Effects of light and group size on the activity of wood frog tadpoles (Rana sylvatica) and their response to a shadow stimulus

Tadpoles are known to behaviorally respond to cues from aquatic predators. However, there are several additional factors that might affect tadpole behavior. We examined the influence of light conditions and group size on the activity of wood frog (Rana sylvatica) tadpoles and their response to a simulated non-aquatic predator (i.e., a shadow stimulus). Activity levels of undisturbed wood frog tadpoles were higher in larger groups (15 tadpoles) than in the smaller groups (5 tadpoles). Activity following exposure to a simulated aerial predator (i.e., a shadow stimulus) was also higher in the larger groups of tadpoles than in the smaller groups. Light conditions did not influence activity level in undisturbed tadpoles, but did affect the response to the shadow stimulus, with the greatest responses being observed under bright light conditions. Our results suggest that the factors influencing tadpole activity can include a diverse range of factors and cues, including lighting conditions and group size

The Southern Galactic Plane Survey: The Test Region

The Southern Galactic Plane Survey (SGPS) is a project to image the HI line emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high resolution using the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope. In this paper we describe the survey details and goals, present lambda 21-cm continuum data, and discuss HI absorption and emission characteristics of the SGPS Test Region (325.5 deg < l < 333.5 deg; -0.5 deg < b < +3.5 deg). We explore the effects of massive stars on the interstellar medium (ISM) through a study of HI shells and the HI environments of HII regions and supernova remnants. We find an HI shell surrounding the HII region RCW 94 which indicates that the region is embedded in a molecular cloud. We give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0 of 4.3 kpc and 4.9 kpc, respectively. We find evidence of interaction with the surrounding HI for both of these remnants. We also present images of a possible new SNR G328.6-0.0. Additionally, we have discovered two small HI shells with no counterparts in continuum emission.Comment: 17 pages, 7 embedded EPS figures, 10 low-res jpeg figures, uses emulateapj5.sty. Accepted for publication in the Astrophysical Journal. Version with all full resolution figures embedded is available at http://www.astro.umn.edu/~naomi/sgps/papers/SGPS.ps.g

Crystal structure of mixed fluorites Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) and luminescence of Eu(2+) in the crystals

Within the framework of the virtual crystal method implemented in the shell model and pair potential approximation the crystal structure of mixed fluorites Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) has been calculated. The impurity center Eu(2+) and the distance Eu(2+)-F in this crystals have been also calculated. The low level position of excited 4f65d configuration of the Eu(2+) ion has been expressed using phenomenological dependence on distance E(2+)-F. The dependences of Stokes shift and Huang-Rhys factor on concentration x have been received for yellow luminescence in Sr(1-x)Ba(x)F(2):Eu(2+). The value x, for which the eg -level of Eu(2+) ion will be in conduction band in Sr(1-x)Ba(x)F(2):Eu(2+) has been calculated.Comment: 8 pages, 3 figures. The manuscript is sent to journal 'Physics of the solid state'. The results will be submitted on inernational conference SCINTMAT'2002 in oral session (june,20-22,2002,Ekaterinburg,Russia). Corresponding author e-mail: [email protected]

Optical spectrum of the post-AGB star HD56126 in the region 4010-8790 AA

We studied in detail the optical spectrum of the post-AGB star HD56126 (IRAS07134+1005). We use high resolution spectra (R=25000 and 60000) obtained with the echelle spectrographs of the 6-m telescope. About one and a half thousand absorptions of neutral atoms and ions, absorption bands of C_2, CN, and CH molecules, and interstellar bands (DIBs) are identified in the 4010 to 8790 AA wavelength region, and the depths and radial velocities of these spectral features are measured. Differences are revealed between the variations of the radial velocities measured from spectral features of different excitation. In addition to the well-known variability of the Halpha profile, we found variations in the profiles of a number of FeII, YII, and BaII lines. We also produce an atlas of the spectrum of HD56126 and its comparison staralpha Per. The full version of the atlas is available in electronic form from Web-address: http://www.sao.ru/hq/ssl/Atlas/Atlas.htmlComment: 42 pages, 6 figure

Photoproduction of Long-Lived Holes and Electronic Processes in Intrinsic Electric Fields Seen through Photoinduced Absorption and Dichroism in Ca_3Ga_{2-x}Mn_xGe_3O_{12} Garnets

Long-lived photoinduced absorption and dichroism in the Ca_3Ga_{2-x}Mn_xGe_3O_{12} garnets with x < 0.06 were examined versus temperature and pumping intensity. Unusual features of the kinetics of photoinduced phenomena are indicative of the underlying electronic processes. The comparison with the case of Ca_3Mn_2Ge_3O_{12}, explored earlier by the authors, permits one to finally establish the main common mechanisms of photoinduced absorption and dichroism caused by random electric fields of photoproduced charges (hole polarons). The rate of their diffusion and relaxation through recombination is strongly influenced by the same fields, whose large statistical straggling is responsible for a broad continuous set of relaxation components (observed in the relaxation time range from 1 to about 1000 min). For Ca_3Ga_{2-x}Mn_xGe_3O_{12}, the time and temperature dependences of photoinduced absorption and dichroism bear a strong imprint of structure imperfection increasing with x.Comment: 20 pages, 10 figure