398 research outputs found
The Petrological Evolution of Garnet-Rich Meta-Igneous Bodies in the Southeastern Adirondack Mountains, New York.
THIRTY YEARS OF CHANGE IN THE PUBLICATION PROCESS
This essay considers changes in the publication process in sociology journals over the last thirty years. Decisions of accept or conditional accept on the first submission have almost disappeared, and the use of revise and resubmit decisions has expanded to cover a wide range of papers. Other important changes have been an increase in the typical number of reviewers and a less active role for editors. The changes have resulted in an improvement of the quality of published papers, but have also had some negative consequences. One is a slowdown in the process. Another is a dominance of one kind of publication â the full-scale research paper â and a decline of other types, including comments, research notes, and essays. The paper concludes by discussing some changes that might encourage a wider variety of publication types and facilitate commentary and debate on published paper
Correlation calculations for the reconstruction of the Si (100) surface
Ab initio multi-reference configuration interaction calculations are
performed for the Si(100) surface using a cluster approach. The convergence
with respect to the cluster size is checked and the final results are taken
from a cluster which models two dimers and six bulk layers. We
find for the ideal as well as for the p() reconstruction a singlet
ground state consisting of several configurations. The energy gain due to
forming the symmetric dimer in the p() structure is 1.75 eV, the
bond length of the dimer is 2.35 \AA which is very close to the bulk value. In
contradiction to the LDA results and in agreement with previous correlation
calculations we do not find an asymmetric p() structure.Comment: 6 pages, Revtex, 3 postscript figures, to appear in Surf. S
Comparative study of dimer vacancies and dimer-vacancy lines on Si(001) and Ge(001)
Although the clean Si(001) and Ge(001) surfaces are very similar, experiments
to date have shown that dimer-vacancy (DV) defects self-organize into vacancy
lines (VLs) on Si(001), but not on Ge(001). In this paper, we perform
empirical-potential calculations aimed at understanding the differences between
the vacancies on Si(001) and Ge(001). We identify three energetic parameters
that characterize the DVs on the two surfaces: the formation energy of a single
DV, the attraction between two DVs in adjacent dimer rows, and the strain
sensitivity of the formation energy of DVs and VLs. At the empirical level of
treatment of the atomic interactions (Tersoff potentials), all three parameters
are favorable for the self-assembly of DVs on the Si(001) surface rather than
on Ge(001). The most significant difference between the defects on Si(001) and
on Ge(001) concerns the formation energy of single DVs, which is three times
larger in the latter case. By calculating the strain-dependent formation
energies of DVs and VLs, we propose that the experimental observation of
self-assembly of vacancies on clean Ge(001) could be achieved by applying
compressive strains of the order of 2%.Comment: 3 tables, 4 figures, to appear in Surface Scienc
Carbon superatom thin films
Assembling clusters on surfaces has emerged as a novel way to grow thin films
with targeted properties. In particular, it has been proposed from experimental
findings that fullerenes deposited on surfaces could give rise to thin films
retaining the bonding properties of the incident clusters. However the
microscopic structure of such films is still unclear. By performing quantum
molecular dynamics simulations, we show that C_28 fullerenes can be deposited
on a surface to form a thin film of nearly defect free molecules, which act as
carbon superatoms. Our findings help clarify the structure of disordered small
fullerene films and also support the recently proposed hyperdiamond model for
solid C_28.Comment: 13 pages, RevTeX, 2 figures available as black and white PostScript
files; color PostScript and/or gif files available upon reques
Lattice-Imposed Geometry in Metal-Organic Frameworks: Lacunary Zn4O Clusters in MOF-5 Serve as Tripodal Chelating Ligands for Ni2+
The inorganic clusters in metalâorganic frameworks can be used to trap metal ions in coordination geometries that are difficult to achieve in molecular chemistry. We illustrate this concept by using the well-known basic carboxylate clusters in Zn[subscript 4]O(1,4-benzenedicarboxylate)3 (MOF-5) as tripodal chelating ligands that enforce an unusual pseudo-tetrahedral oxygen ligand field around Ni[superscript 2+]. The new Ni-based MOF-5 analogue is characterized by porosity measurements and a suite of electronic structure spectroscopies. Classical ligand field analysis of the Ni[superscript 2+] ion isolated in MOF-5 classifies the Zn3O(carboxylate)6 âtripodal ligandâ as an unusual, stronger field ligand than halides and other oxygen donor ligands. These results may inspire the widespread usage of MOFs as chelating ligands for stabilizing site-isolated metal ions in future reactivity and electronic structure studies.United States. Dept. of Energy. Office of Science (Award DE-SC0006937
Structural, optical and magnetic properties of Ni-doped ZnO micro-rods grown by the spray pyrolysis method
Undoped and Ni-doped ZnO micro-rod arrays were successfully synthesized by the spray pyrolysis method on glass substrates. Analysis of the samples with x-ray diffraction and scanning electron microscopy showed that these micro-rod arrays had a polycrystalline wurtzite structure with a highly c-axis preferred orientation. Photoluminescence studies at both 300 K and 10 K show that the incorporation of nickel leads to a relative increase in the visible blue light band intensity. Magnetic measurements indicated that Ni-doped ZnO samples exhibit ferromagnetic behavior at room temperature, which is possibly related to the presence of point defects
Drug interaction: focusing on response surface models
Anesthesiologists have been aware of the importance of optimal drug combination long ago and performed many investigations about the combined use of anesthetic agents. There are 3 classes of drug interaction: additive, synergistic, and antagonistic. These definitions of drug interaction suggest that a zero interaction model should exist to be used as a reference in classifying the interaction of drug combinations. The Loewe additivity has been used as a universal reference model for classifying drug interaction. Most anesthetic drugs follow the sigmoid Emax model (Hill equation); this model will be used for modeling response surface. Among lots of models for drug interaction in the anesthetic area, the Greco model, Machado model, Plummer model, Carter model, Minto model, Fidler model, and Kong model are adequate to be applied to the data of anesthetic drug interaction. A model with a single interaction parameter does not accept an inconsistency in the classes of drug interactions. To solve this problem, some researchers proposed parametric models which have a polynomial interaction function to capture synergy, additivity, and antagonism scattered all over the surface of drug combinations. Inference about truth must be based on an optimal approximating model. Akaike information criterion (AIC) is the most popular approach to choosing the best model among the aforementioned models. Whatever the good qualities of a chosen model, it is uncertain whether the chosen model is the best model. A more robust inference can be extracted from averaging several models that are considered relevant
Cycles in politics : wavelet analysis of political time-series
Spectral analysis and ARMA models have been the most common weapons of choice for
the detection of cycles in political time-series. Controversies about cycles, however, tend to
revolve about an issue that both techniques are badly equipped to address: the possibility
of irregular cycles without fixed periodicity throughout the entire time-series. This has led
to two main consequences. On the one hand, proponents of cyclical theories have often
dismissed established statistical techniques. On the other hand, proponents of established
techniques have dismissed the possibility of cycles without fixed periodicity. Wavelets allow the detection of transient and coexisting cycles and structural breaks in periodicity. In this paper, we present the tools of wavelet analysis and apply them to the study to two lingering puzzles in the political science literature: the existence to cycles in election returns in the United States and in the severity of major power wars.Fundação para a CiĂȘncia e a Tecnologia (FCT
Home media and science performance:A cross-national study
This study examines the effects of media resources in the parental home on the science performance of 15-year-old students. It employs data from the 2006 Programme for International Student Assessment (PISA) containing information on 345,967 respondents from 53 countries. Results show that media assets in the family home are indeed meaningful for childrenâs science performance, as a beneficial resource but also as a disadvantage. A positive reading climate in the parental home and the availability of computers benefits science performance. However, a television-rich home seems to hinder childrenâs school success. Furthermore, results indicate that, compared to less developed countries, in more modernized societies parental reading investments are even more beneficial to their childrenâs science performance, whereas a television-rich parental home is even more disadvantageous
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