31,907 research outputs found
Lanthanide Ionization Energies and the Sub-Shell Break. Part 2. The Third and Fourth Ionization Energies
By interpolating a 4fq6s → 4fq7s transition within the sequence f1 → f14 rather than between f0 and f14, revised third and fourth ionization energies of the lanthanides have been obtained. The revised values, together with the second ionization energies calculated in a previous paper, are used to calculate values of the standard enthalpies of formation of the gaseous tripositive ions, ΔfHƟ(M3+,g), and of the lattice and hydration enthalpies of some lanthanide compounds and ions in the trivalent and tetravalent states. The displacements of f0 values from nearly smooth f1 → f14 variations exceed 30 kJ mol-1 and indicate substantial subshell breaks
Valencies of the lanthanides
The valencies of the lanthanides vary more than was once thought. In addition to valencies associated with a half-full shell, there are valencies associated with a quarter- and three-quarter-full shell. This can be explained on the basis of Slater’s theory of many-electron atoms. The same theory explains the variation in complexing constants in the trivalent state (the “tetrad effect”). Valency in metallic and organometallic compounds is also discussed
Thrifty swimming with shear-thinning
Microscale propulsion is integral to numerous biomedical systems, for example
biofilm formation and human reproduction, where the surrounding fluids comprise
suspensions of polymers. These polymers endow the fluid with non-Newtonian
rheological properties, such as shear-thinning and viscoelasticity. Thus, the
complex dynamics of non-Newtonian fluids presents numerous modelling
challenges, strongly motivating experimental study. Here, we demonstrate that
failing to account for "out-of-plane" effects when analysing experimental data
of undulatory swimming through a shear-thinning fluid results in a significant
overestimate of fluid viscosity around the model swimmer C. elegans. This
miscalculation of viscosity corresponds with an overestimate of the power the
swimmer expends, a key biophysical quantity important for understanding the
internal mechanics of the swimmer. As experimental flow tracking techniques
improve, accurate experimental estimates of power consumption using this
technique will arise in similar undulatory systems, such as the planar beating
of human sperm through cervical mucus, will be required to probe the
interaction between internal power generation, fluid rheology, and the
resulting waveform
Nitrogen abundances in giant stars of the globular cluster NGC 6752
We present N abundances for 21 bright giants in the globular cluster NGC 6752
based on high-resolution UVES spectra of the 3360A NH lines. We confirm that
the Stromgren c1 index traces the N abundance and find that the star-to-star N
abundance variation is 1.95 dex, at the sample's luminosity. We find
statistically significant correlations, but small amplitude variations, between
the abundances of N and alpha-, Fe-peak, and s-process elements. Analyses using
model atmospheres with appropriate N, O, Na, and Al abundances would
strengthen, rather than mute, these correlations. If the small variations of
heavy elements are real, then the synthesis of the N anomalies must take place
in stars which also synthesize alpha-, Fe-peak, and s-process elements. These
correlations offer support for contributions from both AGB and massive stars to
the globular cluster abundance anomalies.Comment: Accepted for publication in Ap
Big Data, Digitization, and Social Change (Ubiquity Symposium)
The term “big data” is something of a misnomer. Every generation of computers since the 1950s has been confronted with problems where data was way too large for the memory and processing power available. This seemed like an inconvenience of the technology that would someday be resolved when the next generation of computers came along. So what is different about big data today? The revolution is happening at the convergence of two trends: the expansion of the internet into billions of computing devices, and the digitization of almost everything. The internet gives us access to vast amounts of data. Digitization creates digital representations for many things once thought to be beyond the reach of computing technology. The result is an explosion of innovation of network-based big data applications and the automation of cognitive tasks. This revolution is introducing what Brynjolfsson and McAfee call the “Second Machine Age.” This symposium will examine this revolution from a number of angles
A Search for Binary Stars at Low Metallicity
We present initial results measuring the companion fraction of metal-poor
stars ([Fe/H]2.0). We are employing the Lick Observatory planet-finding
system to make high-precision Doppler observations of these objects. The binary
fraction of metal-poor stars provides important constraints on star formation
in the early Galaxy (Carney et al. 2003). Although it has been shown that a
majority of solar metallicity stars are in binaries, it is not clear if this is
the case for metal-poor stars. Is there a metallicity floor below which binary
systems do not form or become rare? To test this we are determining binary
fractions at metallicities below [Fe/H]. Our measurments are not as
precise as the planet finders', but we are still finding errors of only 50 to
300 m/s, depending on the signal-to-noise of a spectrum and stellar atmosphere
of the star. At this precision we can be much more complete than previous
studies in our search for stellar companions.Comment: To appear in conference proceedings,"First Stars III", eds. B.
O'Shea, A. Heger & T. Abel. 3 pages, 5 figure
The Effects of Anxiety Producing Stimuli on Visual Perceptual Thresholds: A Study in Perceptual Defense
The purpose of this investigation was to examine experimentally the phenomenon of perceptual defense as it is related to cigarette smoking behavior. In making this examination a population of undergraduate college students was divided into three groups according to their smoking habits. The three groups were identified as smokers, non-smokers, and quitters. A list of smoking related words was equated with a list of neutral words according to their frequency of appearance in print. These lists of words were then combined to form one list with a random distribution of smoking and neutral words, and this list was presented as stimuli to the subjects. The stimulus presentations were made by tachistoscopic projection, and the response thresholds were recorded in units of illumination of the stimulus required for correct identification. The hypothesis that persons who had recently stopped smoking would exhibit the greatest degree of perceptual defense, followed in order by smokers and non-smokers was not supported by the results. Neither was there any significant evidence to support the prediction that perceptual defense would be positively correlated with anxiety as measured by selected scales of the MMPI. A post hoc investigation of the data did reveal that the smoking group contained a significantly greater proportion of persons exhibiting perceptual defense than was found in either of the other groups. It was recommended that additional research of this nature be conducted using a larger sample of older subjects, and incorporating more highly refined tachistoscopic equipment
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