770 research outputs found
Nonperturbative approach to the Hubbard model in C60 cluster
We propose a computational scheme for the Hubbard model in the C60 cluster in
which the interaction with the Fermi sea of charges added to the neutral
molecule is switched on sequentially. This is applied to the calculation of the
balance of charging energies, within a low-energy truncation of the space of
states which produces moderate errors for an intermediate range of the
interaction strength.Comment: 5 pages, Revtex, 2 figure
Raman Scattering Study of Ba-doped C60 with t1g States
Raman spectra are reported for Ba doped fullerides, BaxC60(x=3,4,and 6). The
lowest frequency Hg modes split into five components for Ba4C60 and Ba6C60 even
at room temperature, allowing us a quantitative analysis based on the
electron-phonon couping theory. For the superconducting Ba4C60, the density of
states at the Fermi energy was derived as 7 eV-1, while the total value of
electron-phonon coupling \lambda was found to be 1.0, which is comparable to
that of K3C60. The tangential Ag(2) mode, which is known as a sensitive probe
for the degree of charge transfer on C60 molecule, shows a remarkable shift
depending on the Ba concentration, being roughly consistent with the full
charge transfer from Ba to C60. An effect of hybridization between Ba and C60
\pi orbitals is also discussed.Comment: 15 pages, 6 figures submitted to Phys. Rev. B (December 1,1998
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Characterization of the chemical signatures of air masses observed during the PEM experiments over the western Pacific
Extensive observations of tropospheric trace species during the second NASA Global Tropospheric Experiment Western Pacific Exploratory Mission (PEM-West B) in February-March 1994 showed significant seasonal variability in comparison with the first mission (PEM-West A), conducted in September-October 1991. In this study we adopt a previously established analytical method, i.e., the ratio C2H2/CO as a measure of the relative degree of atmospheric processing, to elucidate the key similarities and variations between the two missions. In addition, the C2H2/CO ratio scheme is combined with the back-trajectory-based and the LIDAR-based air mass classification schemes, respectively, to make in-depth analysis of the seasonal variation between PEM-West A and PEM-West B (hereinafter referred to as PEM-WA and PEM-WB). A large number of compounds, including long-lived NMHCs, CH4, and CO2, are, as expected, well correlated with the ratio C2H2/CO. In comparison with PEM-WA, a significantly larger range of observed C2H2/CO values at the high end for the PEM-WB period indicates that the western Pacific was more impacted by "fresher" source emissions, i.e., faster or more efficient continental outflow. As in the case of PEM-WA, the C2H2/CO scheme complements the back-trajectory air mass classification scheme very well. By combining the two schemes, we found that the atmospheric processing in the region is dominated by atmospheric mixing for the trace species analyzed. This PEM-WB wintertime result is similar to that found in PEM-WA for the autumn. In both cases, photochemical reactions are found to play a significant role in determining the background mixing ratios of trace gases, and in this way the two processes are directly related and dependent upon each other. This analysis also indicates that many of the upper tropospheric air masses encountered over the western Pacific during PEM-WB may have had little impact from eastern Asia's continental surface sources. NOx mixing ratios were significantly enhanced during PEM-WB when compared with PEM-WA, in the upper troposphere's more atmospherically processed air masses. These high levels of NOx resulted in a substantial amount of photochemical production of O3. A lack of corresponding enhancements in surface emission tracers strongly implies that in situ atmospheric sources such as lightning are responsible for the enhanced upper tropospheric NOx. The similarity in NOx values between the northern (higher air traffic) and southern continental air masses together with the indications of a large seasonal shift suggests that aircraft emissions are not the dominant source. However, photochemical recycling cannot be ruled out as this in situ source of NOx. Copyright 1999 by the American Geophysical Union
Education in the working-class home: modes of learning as revealed by nineteenth-century criminal records
The transmission of knowledge and skills within the working-class household greatly troubled social commentators and social policy experts during the first half of the nineteenth century. To prove theories which related criminality to failures in working-class up-bringing, experts and officials embarked upon an ambitious collection of data on incarcerated criminals at various penal institutions. One such institution was the County Gaol at Ipswich. The exceptionally detailed information that survives on families, literacy, education and apprenticeships of the men, women and children imprisoned there has the potential to transform our understanding of the nature of home schooling (broadly interpreted) amongst the working classes in nineteenth-century England. This article uses data sets from prison registers to chart both the incidence and ‘success’ of instruction in reading and writing within the domestic environment. In the process, it highlights the importance of schooling in working-class families, but also the potentially growing significance of the family in occupational training
In-Situ Infrared Transmission Study of Rb- and K-Doped Fullerenes
We have measured the four IR active molecular vibrations in
as a function of doping . We observe
discontinuous changes in the vibrational spectra showing four distinct phases
(presumably , and 6). The and modes
show the largest changes shifting downward in frequency in four steps as the
doping increases. Several new very weak modes are visible in the phase
and are possibly Raman modes becoming weakly optically active. We present
quantitative fits of the data and calculate the electron-phonon coupling of the
IR mode.Comment: 3 pages, Figure 1 included, 3 more figures available by request.
REVTEX v3.0 IRC60DO
Northern Bobwhite Demographics and Resource Selection Are Explained by Prescribed Fire with Grazing and Woody Cover in Southwest Missouri
Understanding the effects of landscape management on northern bobwhite (Colinus virginianus; hereafter, bobwhite) population growth requires information about seasonal- and stage-specific demographic parameters linked across the annual cycle. We review results to date from 3 years (2016–2018) of an intensive field study evaluating drivers of bobwhite population dynamics and resource selection during the breeding and non-breeding season in southwest Missouri, USA using data from adult and juvenile bobwhite fitted with radio-transmitters. Land cover of our study sites ranged from large blocks of native grasslands maintained with prescribed fire and grazing to more traditional management resulting in small patches of grasslands interspersed with food plots, disked idle areas, and woody cover. During the breeding season, relative probability of selection by broods increased in relation to proportion of native grass managed by grazing and burning and proportion of cropland. Brood survival was also greatest on native grasslands burned and grazed within the past 2 growing seasons. During the fall and winter, relative probability of selection by adults increased as woody edge density increased. Fall and winter survival increased as distance from trees increased and decreased as distance to shrubs increased. Our integrated population model indicated that the number of young hatched per female and adult breeding season survival were greatest on sites with the most native grassland managed by prescribed fire with grazing. However, non-breeding season survival was greater on sites with more agriculture or food plots and woody cover. Abundance declined across all sites from 2016 to 2019. Our work suggests that native grasslands managed by prescribed fire with grazing can provide quail habitat superior to traditional management that strived for a mixture of agriculture, woody cover, and grassland. The combination of conservation grazing and fire in native grasslands interspersed with shrubs may provide the greatest chance for bobwhite populations to persist in southwest Missouri and similar landscapes
Electron--Vibron Interactions and Berry Phases in Charged Buckminsterfullerene: Part I
A simple model for electron-vibron interactions on charged
buckminsterfullerene C, , is solved both at weak and
strong couplings. We consider a single vibrational multiplet interacting
with electrons. At strong coupling the semiclassical dynamical
Jahn-Teller theory is valid. The Jahn-Teller distortions are unimodal for
=1,2,4,5 electrons, and bimodal for 3 electrons. The distortions are
quantized as rigid body pseudo--rotators which are subject to geometrical Berry
phases. These impose ground state degeneracies and dramatically change zero
point energies. Exact diagonalization shows that the semiclassical level
degeneracies and ordering survive well into the weak coupling regime. At weak
coupling, we discover an enhancement factor of for the pair binding
energies over their classical values. This has potentially important
implications for superconductivity in fullerides, and demonstrates the
shortcoming of Migdal--Eliashberg theory for molecular crystals.Comment: 29 pages (+7 figures, 3 available upon request), LATEX,
report-number: BM515
Nutrition aspects in children receiving maintenance hemodialysis: impact on outcome
Children with end-stage renal disease (ESRD) have rates of mortality estimated to be 30-times higher than expected for age compared with those of healthy children. Physical manifestations of under-nutrition, such as body mass index (BMI) and low height standard deviation score (SDS), have been associated with increased risk of mortality. Traditional measures, such as height, weight and serum albumin concentration, may not be accurate indicators to assess the nutritional status of children receiving maintenance hemodialysis. Normalized protein catabolic rate (nPCR) has emerged as a better marker of nutritional status of such children. Meeting the special nutritional needs of these children often requires nutritional supplementation, by either the enteral or the parenteral route. Recently, in children receiving maintenance hemodialysis who are malnourished, intradialytic parenteral nutrition (IDPN) has been utilized as a means to provide additional protein and calories. This article is a state-of-the-art review of malnutrition in children receiving maintenance hemodialysis, with special focus on outcome, nPCR and IDPN
Insulating and Conducting Phases of RbC60
Optical measurements were performed on thin films of RbC,
identified by X-ray diffraction as mostly material. The samples were
subjected to various heat treatments, including quenching and slow cooling from
400K. The dramatic increase in the transmission of the quenched samples, and
the relaxation towards the transmission observed in slow cooled samples
provides direct evidence for the existence of a metastable insulating phase.
Slow cooling results in a phase transition between two electrically conducting
phases.Comment: Minor revisions. Submitted to PRB, RevTeX 3.0 file, 2 postscript
figures included, ir_dop
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