bluuebunny/crossref_metadata_2025 huggingface dataset:
The APSA Congressional Fellowship: Value for Faculty from Teaching Colleges
and Universities
Authors: Rose Roger P.
Published: June 2008

During its 55-year history, the APSA Congressional Fellowship Program (CFP) has influenced
much of the best work written about Congress. Top congressional and legislative scholars
like David Mayhew, Alan Rosenthal, David Rohde, Lawrence Dodd, and Barbara Sinclair, to name
just a few, were strongly influenced by their experience as legislative fellows on Capitol
Hill. To cite the most prominent example, David Mayhew remarked that his fellowship year was
integral to his writing of Congress: the Electoral Connection: “Absent my
experience as an APSA Congressional Fellow in 1967–1968, there is not the slightest chance I
would have conceived or written The Electoral Connection” (quoted in Biggs
2003, 143).
Family correlates of fruit and vegetable consumption in children and adolescents: a systematic review
Authors: Pearson Natalie , Biddle Stuart JH , Gorely Trish
Published: June 2008

Objectives

To review associations between the family environment and young people’s fruit and vegetable consumption.

Design

A systematic review. Published English-language (n60) papers were identified using electronic databases and manual searches of personal files and reference lists. Observational research reporting a measure of fruit/vegetable intake for children (aged 6–11 years) and/or adolescents (aged 12–18 years) and at least one potential family correlate of dietary intake was included.

Results

Parental modelling and parental intake were consistently and positively associated with children’s fruit and fruit, juice and vegetable (FJV) consumption. There were also positive associations between home availability, family rules and parental encouragement and children’s fruit and vegetable consumption. Parental intake was positively associated with adolescents’ fruit and vegetable consumption. There were also positive associations between parental occupational status and adolescent fruit consumption and between parental education and adolescents’ FJV consumption.

Conclusions

Our findings highlight the importance of targeting the family environment for the promotion of healthy eating behaviours among children and adolescents. Future interventions should encourage parents to be positive role models by targeting parental intake and to create a supportive home environment through increased encouragement and availability of fruits and vegetables and employing rules to govern eating behaviours. For adolescents, indicators of family circumstances (e.g. parental education) should be used to identify target groups for interventions aimed at promoting healthy eating.
Effectiveness of a community-based intervention to improve nutrition in young children in Senegal: a difference in difference analysis
Authors: Alderman Harold , Ndiaye Biram , Linnemayr Sebastian , Ka Abdoulaye , Rokx Claudia , Dieng Khadidiatou , Mulder-Sibanda Menno
Published: June 2008

There are few studies of community growth promotion as a means of addressing malnutrition that are based on longitudinal analysis of large-scale programmes with adequate controls to construct a counterfactual. The current study uses a difference in difference comparison of cohorts to assess the impact on the proportion of underweight children who lived in villages receiving services provided by the Senegal Nutrition Enhancement Project between 2004 and 2006. The project, designed to extend nutrition and growth promotion intervention into rural areas through non-governmental organisation service providers, significantly lowered the risk of a child having a weight more than 2 sd below international norms. The odds ratio of being underweight for children in programme villages after introduction of the intervention was 0·83 (95% CI 0·686, 1·000), after controlling for regional trends and village and household characteristics. Most measured aspects of health care and health seeking behaviour improved in the treatment relative to the control.
Extending Energy-Filtered Transmission Electron Microscopy (EFTEM) into Three Dimensions Using Electron Tomography
Authors: Weyland Matthew , Midgley Paul A.
Published: June 2008

The length scales on which materials microstructures are being formed, grown, and even designed are becoming increasingly small and increasingly three-dimensional. For such complex structures two-dimensional transmission electron microscopy (TEM) analysis is often inadequate and occasionally misleading. One approach to this problem is the modification of electron tomography techniques, developed for structural biology, for use in materials science. Energy-Filtered (EF) TEM elemental distribution images approximate to true projections of structure, and, as such, can be used to reconstruct the three-dimensional distribution of chemical species. A sample holder has been modified to allow the high tilt (±60°) required for tomography and a semiautomatic acquisition script designed to manage energy-loss acquisition. Tilt series data sets have been acquired from two widely different experimental systems, Cr carbides in 316 stainless steel and magnetite nanocrystals in magnetotactic bacteria, demonstrating single- and multiple-element tomography. It is shown that both elemental maps and jump-ratio images are suitable for reconstruction, despite the effects of diffraction contrast in the former and thickness changes in the latter. It is concluded that the image contrast, signal, and signal-to-noise ratio (SNR) are key to the achievable reconstruction quality and, as such, the technique may be of limited value for high energy loss/small inelastic cross section edges.
Analysis of Orientations of Collagen Fibers by Novel Fiber-Tracking Software
Authors: Wu Jun , Rajwa Bartłomiej , Filmer David L. , Hoffmann Christoph M. , Yuan Bo , Chiang Ching-Shoei , Sturgis Jennie , Robinson J. Paul
Published: June 2008

Recent evidence supports the notion that biological functions of extracellular matrix (ECM) are highly correlated to not only its composition but also its structure. This article integrates confocal microscopy imaging and image-processing techniques to analyze the microstructural properties of ECM. This report describes a two- and three-dimensional fiber middle-line tracing algorithm that may be used to quantify collagen fibril organization. We utilized computer simulation and statistical analysis to validate the developed algorithm. These algorithms were applied to confocal images of collagen gels made with reconstituted bovine collagen type I, to demonstrate the computation of orientations of individual fibers.
Angioarchitecture of Tumors Induced by Two Different Cloned Cell Lines Established from a Transplantable Rat Malignant Fibrous Histiocytoma
Authors: Tsunenari Ichiro , Yamate Jyoji , Iwaki Masae , Kuwamura Mitsuru , Kotani Takao , Sakuma Sadashige
Published: June 2008

Angiogenesis, a biologic process whereby endothelial cells divide and migrate to form new blood vessels, is a key step in tumor growth, invasion, and metastasis. In the present study, we investigated the differences in angioarchitecture between two different tumors induced by cloned cell lines (MT-8 and MT-9), derived from a transplantable rat malignant fibrous histiocytoma, by scanning electron microscopy of vascular corrosion casts. During a 3-week observation period after implantation, the growth of MT-8 tumors appeared to be faster than that of MT-9 tumors. Histologically, MT-8 tumors were of the uniformly undifferentiated sarcoma type arranged in characteristic organoid structures, and MT-9 tumors showed a storiform growth pattern. In MT-8 tumors, neovascularization occurred by sprouting at postimplantation (PI) week 1, and the newly formed capillaries gradually became more tortuous. In MT-9 tumors, at PI week 1, the corrosion casts of newly formed capillaries mainly showed a wavy course but no fingerlike outgrowths of capillaries were seen. At PI weeks 2 and 3, the sprouting was seen specifically in MT-9 tumors, forming basketlike structures and glomeruloid structures of capillaries. These results indicate that angiogenesis or angioarchitecture of MT-8 tumors is different from that of MT-9 tumors, depending on the differences in their tumor histology and by the features like absence or presence of basketlike structures and glomeruloid structures of capillaries.
Electron Beam Coater for Reduction of Charging in Ice-Embedded
Biological Specimens using Ti88Si12 Alloy
Authors: Sherman Michael B. , Chiu Wah
Published: June 2008

Biological macromolecules embedded in vitreous ice are known to
suffer from charging while being imaged in an electron transmission
cryomicroscope. We developed an electron beam coater that deposits
conductive films onto the surface of frozen-hydrated specimens. The
conductive films help to dissipate charge during electron irradiation
of poorly conductive ice-embedded biological samples. We observed
significant reduction in charging of ice-embedded catalase crystals
suspended over holes in a holey carbon film after coating them with a
30-Å-thick layer of an amorphous alloy,
Ti88Si12. Images of the crystals after coating
showed diffraction spots of up to 3 Å resolution.
Using Fluctuation Microscopy to Characterize Structural Order in
Metallic Glasses
Authors: Li Jing , Gu X. , Hufnagel T.C.
Published: June 2008

We have used fluctuation microscopy to reveal the presence of
structural order on length scales of 1–2 nm in metallic glasses.
We compare results of fluctuation microscopy measurements with high
resolution transmission electron microscopy and electron diffraction
observations on a series of metallic glass samples with differing
degrees of structural order. The agreement between the fluctuation
microscopy results and those of the other techniques is good. In
particular, we show that the technique used to make thin specimens for
electron microscopy affects the structure of the metallic glass, with
ion thinning inducing more structural order than electropolishing. We
also show that relatively minor changes in the composition of the alloy
can have a significant effect on the medium-range order; this increased
order is correlated with changes in mechanical behavior.
Object Oriented Database and Electronic Notebook for Transmission
Electron Microscopy
Authors: Ludtke Steven J. , Nason Laurie , Tu Haili , Peng Liwei , Chiu Wah
Published: June 2008

As high-resolution biological transmission electron microscopy (TEM)
has increased in popularity over recent years, the volume of data and
number of projects underway has risen dramatically. A robust tool for
effective data management is essential to efficiently process large
data sets and extract maximum information from the available data. We
present the Electron Microscopy Electronic Notebook (EMEN), a portable,
object-oriented, web-based tool for TEM data archival and project
management. EMEN has several unique features. First, the database is
logically organized and annotated so multiple collaborators at
different geographical locations can easily access and interpret the
data without assistance. Second, the database was designed to provide
flexibility to the user, so it can be used much as a lab notebook would
be, while maintaining a structure suitable for data mining and direct
interaction with data-processing software. Finally, as an
object-oriented database, the database structure is dynamic and can be
easily extended to incorporate information not defined in the original
database specification.
The Use of High Pressure Freezing and Freeze Substitution to Study Host–Pathogen Interactions in Fungal Diseases of Plants
Authors: Mims C.W. , Celio Gail J. , Richardson Elizabeth A.
Published: June 2008

This article reports on the use of high pressure freezing followed by freeze substitution (HPF/FS) to study ultrastructural details of host–pathogen interactions in fungal diseases of plants. The specific host–pathogen systems discussed here include a powdery mildew infection of poinsettia and rust infections of daylily and Indian strawberry. The three pathogens considered here all attack the leaves of their hosts and produce specialized hyphal branches known as haustoria that invade individual host cells without killing them. We found that HPF/FS provided excellent preservation of both haustoria and host cells for all three host–pathogen systems. Preservation of fungal and host cell membranes was particularly good and greatly facilitated the detailed study of host–pathogen interfaces. In some instances, HPF/FS provided information that was not available in samples prepared for study using conventional chemical fixation. On the other hand, we did encounter various problems associated with the use of HPF/FS. Examples included freeze damage of samples, inconsistency of fixation in different samples, separation of plant cell cytoplasm from cell walls, breakage of cell walls and membranes, and splitting of thin sections. However, we believe that the outstanding preservation of ultrastructural details afforded by HPF/FS significantly outweighs these problems and we highly recommend the use of this fixation protocol for future studies of fungal host-plant interactions.
Thin Dielectric Film Thickness Determination by Advanced Transmission Electron Microscopy
Authors: Diebold A.C. , Foran B. , Kisielowski C. , Muller D.A. , Pennycook S.J. , Principe E. , Stemmer S.
Published: June 2008

High-resolution transmission electron microscopy (HR-TEM) has been used as the ultimate method of thickness measurement for thin films. The appearance of phase contrast interference patterns in HR-TEM images has long been confused as the appearance of a crystal lattice by nonspecialists. Relatively easy to interpret crystal lattice images are now directly observed with the introduction of annular dark-field detectors for scanning TEM (STEM). With the recent development of reliable lattice image processing software that creates crystal structure images from phase contrast data, HR-TEM can also provide crystal lattice images. The resolution of both methods has been steadily improved reaching now into the sub-Ångstrom region. Improvements in electron lens and image analysis software are increasing the spatial resolution of both methods. Optimum resolution for STEM requires that the probe beam be highly localized. In STEM, beam localization is enhanced by selection of the correct aperture. When STEM measurement is done using a highly localized probe beam, HR-TEM and STEM measurement of the thickness of silicon oxynitride films agree within experimental error. In this article, the optimum conditions for HR-TEM and STEM measurement are discussed along with a method for repeatable film thickness determination. The impact of sample thickness is also discussed. The key result in this article is the proposal of a reproducible method for film thickness determination.
Letter to the Editor: Comments on “Compositional Averaging of
Backscatter Intensities in Compounds,” with a Response from
Donovan
Authors: Reed S.J.B.
Published: June 2008

The electron backscatter coefficient (η) and the related
correction factor for X-ray intensity (R) are both strongly
dependent on atomic number and although quite good data are available
for pure elements, the derivation of values for compounds is
problematic. This issue is addressed by Donovan, Pingitore, and
Westphal (Microscopy and Microanalysis, Vol. 9, No. 3, June
2003, pp. 202–215), in which an “electron fraction”
averaging method is advocated as an improvement on
“traditional” mass fraction averaging, which is known to be
only an approximation. (The difference, according to Table 3, is only
significant, however, for samples containing heavy elements such as Pb
and Th.) New thinking on this topic is welcome, but I believe this
proposal should be treated with caution pending more rigorous
testing.
1st INCF Workshop on Sustainability of Neuroscience Databases
Authors: Van Horn Jack , van Pelt Jaap
Published: June 2008

The goal of the workshop was to discuss issues related to the sustainability of neuroscience databases, identify problems and propose solutions, and formulate recommendations to the INCF. The report summarizes the discussions of invited participants from the neuroinformatics community as well as from other disciplines where sustainability issues have already been approached. The recommendations for the INCF involve rating, ranking, and supporting database sustainability.
Which in vitro models could be best used to study hepatocyte polarity?
Authors: Decaens Catherine , Durand Marjorie , Grosse Brigitte , Cassio Doris
Published: June 2008

The correct functioning of the liver is ensured by the setting and the maintenance of hepatocyte polarity. The complex polarity of the hepatocyte is characterized by the existence of several basolateral and apical poles per cell. Many in vitro models are available for studying hepatocyte polarity, but which are the more suitable? To answer this question, we aimed to identify criteria which determine the typical hepatocyte polarity. Therefore, we compiled a range of protein markers of membrane domains in rat hepatocytes and investigated their involvement in hepatocytic functions. Then, we focused on the relationship between hepatic functions and the cytoskeleton, Golgi apparatus and endoplasmic reticulum. Subsequently, we compared different cell lines expressing hepatocyte polarity. Finally, to demonstrate the usefulness of some of these lines, we presented new data on endoplasmic reticulum organization in relation to polarity.
Ability of PknA, a mycobacterial eukaryotic-type serine/threonine kinase, to transphosphorylate MurD, a ligase involved in the process of peptidoglycan biosynthesis
Authors: Thakur Meghna , Chakraborti Pradip K.
Published: June 2008

Eukaryotic-type serine/threonine protein kinases in bacteria have been implicated in controlling a host of cellular activities. PknA is one of eleven such protein kinases from Mycobacterium tuberculosis which regulates morphological changes associated with cell division. In the present study we provide the evidence for the ability of PknA to transphosphorylate mMurD (mycobacterial UDP-N-acetylmuramoyl-L-alanine:D-glutamate-ligase), the enzyme involved in peptidoglycan biosynthesis. Its co-expression in Escherichia coli along with PknA resulted in phosphorylation of mMurD. Consistent with these observations, results of the solid-phase binding assays revealed a high-affinity in vitro binding between the two proteins. Furthermore, overexpression of m-murD in Mycobacterium smegmatis yielded a phosphorylated protein. The results of the present study therefore point towards the possibility of mMurD being a substrate of PknA.
PKCβII modulates translation independently from mTOR and through RACK1
Authors: Grosso Stefano , Volta Viviana , Sala Leonardo A. , Vietri Marina , Marchisio Pier Carlo , Ron Dorit , Biffo Stefano
Published: June 2008

RACK1 (receptor for activated C kinase 1) is an abundant scaffolding protein, which binds active PKCβII (protein kinase C βII) increasing its activity in vitro. RACK1 has also been described as a component of the small ribosomal subunit, in proximity to the mRNA exit channel. In the present study we tested the hypothesis that PKCβII plays a specific role in translational control and verified whether it may associate with the ribosomal machinery. We find that specific inhibition of PKCβI/II reduces translation as well as global PKC inhibition, but without affecting phosphorylation of mTOR (mammalian target of rapamycin) targets. These results suggest that PKCβII acts as a specific PKC isoform affecting translation in an mTOR-independent fashion, possibly close to the ribosomal machinery. Using far-Western analysis, we found that PKCβII binds ribosomes in vitro. Co-immunoprecipitation studies indicate that a small but reproducible pool of PKCβII is associated with membranes containing ribosomes, suggesting that in vivo PKCβII may also physically interact with the ribosomal machinery. Polysomal profiles show that stimulation of PKC results in an increased polysomes/80S ratio, associated with a shift of PKCβII to the heavier part of the gradient. A RACK1-derived peptide that inhibits the binding of active PKCβII to RACK1 reduces the polysomes/80S ratio and methionine incorporation, suggesting that binding of PKCβII to RACK1 is important for PKC-mediated translational control. Finally, down-regulation of RACK1 by siRNA (small interfering RNA) impairs the PKC-mediated increase of translation. Taken together the results of the present study show that PKCβII can act as a specific PKC isoform regulating translation, in an mTOR-independent fashion, possibly close to the ribosomal machinery.
CD36 N-terminal cytoplasmic domain is not required for the internalization of oxidized low-density lipoprotein
Authors: McDermott-Roe Chris , Martin Juliette , Collot-Teixeira Sophie , McGregor John L.
Published: June 2008

The uptake of OxLDLs (oxidized low density lipoproteins) by CD36-expressing macrophages in the arterial intima and the subsequent ‘foam cell’ formation represents a crucial step in the initiation and development of atherosclerotic plaques. The present study has addressed the function of the CD36 N-terminal cytoplasmic domain in the binding and internalization of OxLDL. A selection of CD36 N-terminal cytoplasmic domain mutants were generated and stably expressed in HEK-293 (human embryonic kidney) cells. The capacity of three mutants [CD36_C3/7-A (CD36-C3A/C7A), CD36_D4/R5-A (CD36-D4A/R5A) and CD36_nCPD− (CD36 lacking the N-terminal cytoplasmic domain)] to bind and endocytose OxLDL was then studied using immunofluorescence microscopy and quantitative fluorimetry. Each of the CD36 constructs was expressed at differing levels at the cell surface, as measured by flow cytometry and Western blotting. Following incubation with DiI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate)–OxLDL, cells bearing the CD36_wt (wild-type CD36), CD36_C3/7-A, CD36_D4/R5-A and CD36_nCPD− constructs all internalized DiI–OxLDL into endosomal structures, whereas empty-vector-transfected cells failed to do so, indicating that, unlike the C-terminal cytoplasmic domain, the N-terminal cytoplasmic domain is not essential for the endocytosis of OxLDL. In conclusion, the uptake of OxLDL by CD36 is not reliant on the presence of the CD36 N-terminal cytoplasmic domain. However, the N-terminal cytoplasmic domain may conceivably be implicated in the maturation of CD36.
Tyrosine kinase signalling in embryonic stem cells
Authors: Annerén Cecilia
Published: June 2008

Pluripotent ES (embryonic stem) cells can be expanded in culture and induced to differentiate into a wide range of cell types. Self-renewal of ES cells involves proliferation with concomitant suppression of differentiation. Some critical and conserved pathways regulating self-renewal in both human and mouse ES cells have been identified, but there is also evidence suggesting significant species differences. Cytoplasmic and receptor tyrosine kinases play important roles in proliferation, survival, self-renewal and differentiation in stem, progenitor and adult cells. The present review focuses on the role of tyrosine kinase signalling for maintenance of the undifferentiated state, proliferation, survival and early differentiation of ES cells.
Periodic orbit analysis demonstrates genetic constraints, variability, and switching in Drosophila courtship behavior
Authors: Stoop Ruedi , Arthur Benjamin I.
Published: June 2008

We use symbolic dynamics to describe Drosophila courtship communication. We posit that behavior should be defined in terms of irreducible periodic orbits of fundamental acts. This leads to a first operational definition of behavior, which allows for a fine grained quantitative analysis of behavior. We obtain evidence that during Drosophila courtship, individual characteristics of the protagonists are exchanged (predominantly from the male to the female) and that males in the presence of fruitless males perform a behavioral switch from male to female behavior.
Amorphous Ge quantum dots embedded in SiO2 formed by low energy ion implantation
Authors: Zhao J. P. , Huang D. X. , Chen Z. Y. , Chu W. K. , Makarenkov B. , Jacobson A. J. , Bahrim B. , Rabalais J. W.
Published: June 2008

Under ultrahigh vacuum conditions, extremely small Ge nanodots embedded in SiO2, i.e., Ge–SiO2 quantum dot composites, have been formed by ion implantation of Ge+74 isotope into (0001) Z-cut quartz at a low kinetic energy of 9keV using varying implantation temperatures. Transmission electron microscopy (TEM) images and micro-Raman scattering show that amorphous Ge nanodots are formed at all temperatures. The formation of amorphous Ge nanodots is different from reported crystalline Ge nanodot formation by high energy ion implantation followed by a necessary high temperature annealing process. At room temperature, a confined spatial distribution of the amorphous Ge nanodots can be obtained. Ge inward diffusion was found to be significantly enhanced by a synergetic effect of high implantation temperature and preferential sputtering of surface oxygen, which induced a much wider and deeper Ge nanodot distribution at elevated implantation temperature. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. Cross-sectional TEM observation and the depth profile of Ge atoms in SiO2 obtained from x-ray photoelectron spectra revealed a critical Ge concentration for observable amorphous nanodot formation. The mechanism of formation of amorphous Ge nanodots and the change in spatial distribution with implantation temperature are discussed.
Identifying almost invariant sets in stochastic dynamical systems
Authors: Billings Lora , Schwartz Ira B.
Published: June 2008

We consider the approximation of fluctuation induced almost invariant sets arising from stochastic dynamical systems. The dynamical evolution of densities is derived from the stochastic Frobenius–Perron operator. Given a stochastic kernel with a known distribution, approximate almost invariant sets are found by translating the problem into an eigenvalue problem derived from reversible Markov processes. Analytic and computational examples of the methods are used to illustrate the technique, and are shown to reveal the probability transport between almost invariant sets in nonlinear stochastic systems. Both small and large noise cases are considered.
Photodissociation and collisional cooling of rhodamine 575 cations in a quadrupole ion trap
Authors: Sassin Nicholas A. , Everhart Stephanie C. , Cline Joseph I. , Ervin Kent M.
Published: June 2008

The photodissociation of rhodamine 575 cations held in a quadrupole ion trap is studied using 514nm light as a function of buffer gas pressure, irradiation time, and laser fluence. The laser-induced photodissociation decays of rhodamine ions have lifetimes on the order of seconds for the range of pressures and powers investigated and exhibit strong nonlinear pressure dependence. Dissociation mechanisms are considered that involve the sequential absorption of multiple photons and several collisional deactivation steps.
Resonant tunneling as a dominant transport mechanism in n-GaAs∕p-GaAs tunnel diodes
Authors: Jandieri K. , Baranovskii S. D. , Rubel O. , Stolz W. , Gebhard F. , Guter W. , Hermle M. , Bett A. W.
Published: June 2008

Current-voltage characteristics of Ga0.99In0.01As tunnel diodes are studied experimentally and theoretically. Three possible tunneling mechanisms are considered: direct band-to-band tunneling, phonon-assisted tunneling through defects, and resonant tunneling through defects. Comparison between theoretical results and experimental data reveals resonant tunneling through oxygen-related defects as the dominant transport mechanism at voltages corresponding to the peak current in diodes with doping level about 1019cm−3.
Single beam optical tweezers setup with backscattered light detection for three-dimensional measurements on DNA and nanopores
Authors: Sischka Andy , Kleimann Christoph , Hachmann Wiebke , Schäfer Marcus M. , Seuffert Ina , Tönsing Katja , Anselmetti Dario
Published: June 2008

We introduce a versatile and high precision three-dimensional optical tweezers setup with minimal optical interference to measure small forces and manipulate single molecules in the vicinity of a weak reflective surface. Our tweezers system integrates an inverted optical microscope with a single IR-laser beam that is spatially filtered in an appropriate way to allow force measurements in three dimensions with remarkably high precision when operated in backscattered light detection mode. The setup was tested by overstretching a λ-DNA in x and z directions (perpendicular and along the optical axis), and by manipulating individual λ-DNA molecules in the vicinity of a nanopore that allowed quantitative single molecule threading experiments with minimal optical interference.
Quantum efficiency improvement in anthracene-based organic light-emitting diodes codoped with a hole-trapping material
Authors: Jarikov Viktor V.
Published: June 2008

We focus on organic light-emitting diodes having an N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB) hole-transport layer, a doped light-emitting layer (LEL) based on a 9,10-diarylanthracene (DAA), and a tris(8-quinolinolato)aluminum (Alq) electron-transport layer. The addition of a hole-trapping codopant, e.g., NPB, to the LEL can triple the external quantum efficiency (EQE), which can reach 3%–6%. We discuss (a) the magnitude of the effect and the causes, (b) the effect on the drive voltage, emission spectrum, and operating lifetime, and (c) the approaches to higher EQEs of 5%–10%. We compare (a) various blue and green LEL dopants, (b) NPB codopant with aminated polycyclic aromatic hydrocarbons, which reduce the EQE, and (c) the DAA-based cells with their Alq-based counterparts.
Large reversible magnetocaloric effect in Tb3Co compound
Authors: Li B. , Du J. , Ren W. J. , Hu W. J. , Zhang Q. , Li D. , Zhang Z. D.
Published: June 2008

A large reversible magnetocaloric effect has been observed in Tb3Co compound. Under a magnetic field change of 5T, the maximum value of magnetic entropy change ΔSM is −18Jkg−1K−1 at 84K and the relative cooling power is 738Jkg−1 with no hysteresis loss. In particular, the large reversible ΔSMmax, −8.5Jkg−1K−1, is achieved for a low magnetic field change of 2T. The magnetic anisotropy and the texture of the material greatly affect ΔSM. The large reversible magnetocaloric effect (both the large ΔSM and the high relative cooling power) indicates that Tb3Co could be a promising candidate for magnetic refrigeration.
Optical cavity modes in gold shell colloids
Authors: Penninkhof J. J. , Sweatlock L. A. , Moroz A. , Atwater H. A. , van Blaaderen A. , Polman A.
Published: June 2008

Core-shell colloids composed of a dielectric core surrounded by a metal shell show geometric cavity resonances with optical properties that are distinctly different than those of the collective plasmon modes of the metal shell. We use finite-difference time domain calculations on silica colloids with a core diameter of 456nm, surrounded by a 38nm thick Au shell, to study the temporal evolution of the mode field intensity inside the cavity upon pulsed excitation. Calculations using Mie theory and the T-matrix method are used to analytically determine the dipolar cavity resonance spectrum, which is found superimposed on the broad collective dipolar plasmonic resonance modes. We characterize resonance wavelength and linewidth in terms of a geometric mode confined inside the cavity. Cavity linewidth can be controlled by metal shell thickness and quality factors Q>150 are observed. Due to the small cavity mode volume V=0.2(λ∕n)3, a Purcell factor as high as P=54 is calculated. Introducing shape anisotropy lifts the cavity mode degeneracy, yielding blue- and redshifted longitudinal and transverse resonant modes, respectively. The relatively large volume over which the field enhancement is observed in these spherical and anisotropic metal shell cavities, combined with cavity quality factors that are much higher than that of the collective plasmonic modes, makes them attractive for application in nanoscale light sources, sensors, or lasers.
Giant random telegraph signal generated by single charge trapping in submicron n-metal-oxide-semiconductor field-effect transistors
Authors: Prati Enrico , Fanciulli Marco , Ferrari Giorgio , Sampietro Marco
Published: June 2008

We report on the current fluctuations of random telegraph signal experimentally observed at cryogenic temperatures in ordinary submicron Si∕SiO2 metal-oxide-semiconductor field-effect transistors (MOSFETs). A giant drain current fluctuation ΔI∕I up to 55% is observed at sub-Kelvin temperature in samples with a large channel width. The current variation is compatible with predictions for decanano MOSFETs at room temperature. The similarity suggests the formation of a quasi-one-dimensional conduction channel at gate voltages sufficiently close to the threshold voltage.
CdTeO
x
to CdTeO3 structural phase transition in as-grown polycrystalline films by reactive sputtering
Authors: Carmona-Rodríguez J. , Lozada-Morales R. , Jiménez-Sandoval O. , Rodríguez-Melgarejo F. , Meléndez-Lira M. , Jiménez-Sandoval S. J.
Published: June 2008

Polycrystalline thin films of CdTeOx (x<3) and CdTeO3 were grown at 400 °C by rf-reactive sputtering. The CdTe oxide films were elaborated in an Ar–O2 atmosphere using different oxygen flow rates in the 5–11 SCCM (SCCM denotes cubic centimeter per minute at STP) range. The structural properties of the samples were studied by x-ray diffraction and micro-Raman spectroscopy. The diffraction patterns show that the films grown with oxygen flows between 5 and 10.5 SCCM present a crystalline structure similar to that of pure CdTe films, that is, a mixture of cubic zinc-blende-type and hexagonal wurtzite-type structures. However, the diffraction patterns of samples grown under an oxygen flow rate of 11 SCCM are strikingly different and in agreement with that of cubic CdTeO3, indicating that a structural phase transition was achieved. These results are in accordance with those obtained by micro-Raman spectroscopy, where the spectra of the CdTeOx samples grown with oxygen flows below 11 SCCM show an intense LO CdTe-like peak at 166 cm−1, which is no longer observable for the CdTeO3 sample. Instead, the Raman spectrum in this case is dominated by two broad bands in the 550–800 cm−1 range, which have been ascribed to the vibrational modes of TeO3 structural subunits. The optical properties, as determined by optical absorption and photoreflectance spectroscopies, are in correspondence with the structural and chemical changes induced by the incorporation of oxygen. The band gap varied between 1.55 and 3.3 eV, the last value corresponding to CdTeO3 films.
How hole defects modify vortex dynamics in ferromagnetic nanodisks
Authors: Moura-Melo W. A. , Pereira A. R. , Silva R. L. , Oliveira-Neto N. M.
Published: June 2008

Defects introduced in ferromagnetic nanodisks may deeply affect the structure and dynamics of stable vortexlike magnetization. Here, analytical techniques are used for studying, among other dynamical aspects, how a small cylindrical cavity modifies the oscillatory modes of the vortex. For instance, we have realized that if the vortex is nucleated out from the hole, its gyrotropic frequencies are shifted below. Modifications become even more pronounced when the vortex core is partially or completely captured by the hole. In these cases, the gyrovector can be partially or completely suppressed, so that the associated frequencies increase considerably, say, from some times to several powers. Possible relevance of our results for understanding other aspects of vortex dynamics in the presence of cavities and/or structural defects are also discussed.
First-principles effective Hamiltonian for ferroelectric polarization inBaTiO3/SrTiO3 superlattices
Authors: Lee Jun Hee , Waghmare Umesh V. , Yu Jaejun
Published: June 2008

We present an effective Hamiltonian for the description of ferroelectric polarizations in perovskite oxide superlattices. To understand the ferroelectric behavior of (BaTiO3)n/(SrTiO3)m superlattices, we constrained the local distortion modes along the c direction only and set up the effective Hamiltonian based on the local modes that capture the physics of long-wavelength acoustic modes (strain) and lowest energy transverse optical phonon modes (soft modes) as prescribed by the localized Wannier functions. All the parameters in this effective Hamiltonian were predetermined from the first-principles density-functional theory calculations of each BaTiO3 and SrTiO3 components. As an application of the model parameters, we calculated the polarizations of (BaTiO3)n/(SrTiO3)m with n+m=5, the results of which are in good agreement with those of the previous first-principles calculations of average polarizations as well as local polarizations. This effective Hamiltonian procedure can provide guidance for developing ferroelectric model of other kinds of oxide superlattices.
Transmission electron microscopy studies and simulation of the indentation response of superelastic fullerenelike carbon nitride thin films
Authors: Neidhardt J. , Walter C. , Molina-Aldareguia J. M. , Herrmann M. , Clegg W. J. , Hultman L.
Published: June 2008

The highly elastic behavior of fullerenelike carbon nitride thin films on single crystal Si (001) substrates has been studied by nanoindentation. The films exhibit a microstructure of frequently bent and intersecting graphene sheets. Transmission electron microscopy of indented areas revealed no tendency to plastic deformation in the highly elastic and compliant film. Also, a unique deformation pattern in the Si substrate is observed, where a {111} facetted inverted pyramid of untransformed Si remained intact under the indenter with a retained CNx/Si(001) interface. Analytical approaches using the effective indenter method, supported by finite element methods, are employed to understand the nonlinear but fully elastic behavior of the coatings as well as to describe the critical parameters for the deformation and phase transformation of the Si substrate.
Elimination of dimethyl methylphosphonate by plasma flame made of microwave plasma and burning hydrocarbon fuel
Authors: Cho S. C. , Uhm H. S. , Hong Y. C. , Park Y. G. , Park J. S.
Published: June 2008

Elimination of dimethyl methylphosphonate (DMMP) in liquid phase was studied by making use of a microwave plasma burner, exhibiting a safe removal capability of stockpiled chemical weapons. The microwave plasma burner consisted of a fuel injector and a plasma flame exit connected in series to a microwave plasma torch. The burner flames were sustained by injecting hydrocarbon fuels into the microwave plasma torch in air discharge. The Fourier transform infrared spectra indicated near perfect elimination of DMMP in the microwave plasma burner. This was confirmed by gas chromatography spectra as supporting data, revealing the disappearance of even intermediary compounds in the process of DMMP destruction. The experimental results and the physical configuration of the microwave plasma burner may provide an effective means of on-site removal of chemical warfare agents found on a battlefield.
First principles site occupation and migration of hydrogen, helium, and oxygen in β-phase erbium hydride
Authors: Wixom R. R. , Browning J. F. , Snow C. S. , Schultz P. A. , Jennison D. R.
Published: June 2008

First principles density functional methods were used to investigate the atomistic behavior of hydrogen, helium, and oxygen in β-phase ErH2. The ground state for hydrogen was indeed determined to be the tetrahedral position as commonly assumed, but if the surrounding tetrahedral sites are filled, any additional hydrogen will occupy the octahedral site. Only a small amount of thermally generated tetrahedral-vacancy octahedral-occupancy pairs are predicted at equilibrium since the formation energy is 1.21 eV. Other possible scenarios that result in octahedral hydrogen occupation include a H/Er ratio >2.0 and the presence of oxygen in the lattice. Our calculations indicate that oxygen impurities will reside in tetrahedral sites, even if that site is already occupied and hydrogen must be displaced into a neighboring octahedral site. Oxygen will migrate at moderate temperatures by jumping between tetrahedral and octahedral sites. The extent of hydrogen self-diffusion will depend on the concentration of tetrahedral vacancies and/or octahedral hydrogen and therefore can be modified by changing the H/Er ratio or by impurities (such as oxygen) that create octahedral hydrogen occupation. In samples where some of the hydrogen is replaced with tritium, helium generated by tritium decay will favor a tetrahedral site left vacant by a transmuted tritium. The barrier to helium migration between two unoccupied neighboring tetrahedral sites is 0.49 eV, where the path maximum corresponds to the octahedral site. If an extended network of neighboring vacancies exists, the relatively small barrier provides that helium may move throughout that network at room temperature. Given enough energy to escape the tetrahedral site(s), 1.31 eV, helium may continue to migrate by a 0.88 eV concerted-motion mechanism—temporarily displacing hydrogen as it moves between empty octahedral sites and filled tetrahedral sites.
Absolute calibration of imaging plate for GeV electrons
Authors: Nakanii N. , Kondo K. , Yabuuchi T. , Tsuji K. , Tanaka K. A. , Suzuki S. , Asaka T. , Yanagida K. , Hanaki H. , Kobayashi T. , Makino K. , Yamane T. , Miyamoto S. , Horikawa K.
Published: June 2008

An imaging plate has been used as a useful detector of energetic electrons in laser electron acceleration and laser fusion studies. The absolute sensitivity of an imaging plate was calibrated at 1GeV electron energy using the injector Linac of SPring-8. The sensitivity curve obtained up to 100MeV in a previous study was extended successfully to GeV range.
Extremal covariant positive operator valued measures: The case of a compact symmetry group
Authors: Carmeli Claudio , Heinosaari Teiko , Pellonpää Juha-Pekka , Toigo Alessandro
Published: June 2008

Given a unitary representation U of a compact group G and a transitive G-space Ω, we characterize the extremal elements of the convex set of all U-covariant positive operator valued measures.
Kondo effect in single cobalt phthalocyanine molecules adsorbed on Au(111) monoatomic steps
Authors: Zhao Aidi , Hu Zhenpeng , Wang Bing , Xiao Xudong , Yang Jinlong , Hou J. G.
Published: June 2008

The Kondo effect in single dehydrogenated cobalt phthalocyanine (CoPc) molecules adsorbed on Au(111) monoatomic steps was studied with a low temperature scanning tunneling microscope. The CoPc molecules adsorbed on Au(111) monoatomic steps show two typical configurations, which can be dehydrogenated to reveal Kondo effect. Moreover, the Kondo temperatures (TK) measured for different molecules vary in a large range from ∼150to∼550K, increasing monotonically with decreasing Co–Au distance. A simple model consisting of a single Co 3dz2 orbital and a Au 6s orbital is considered and gives a qualitative explanation to the dependence. The large variation of TK is attributed to the variation of the interaction between the magnetic-active cobalt ion and the Au substrate resulted from different Co–Au distances.
Nonmagnetic compensation in ferromagnetic Ga1−xMnxAs and Ga1−xMnxP synthesized by ion implantation and pulsed-laser melting
Authors: Scarpulla M. A. , Stone P. R. , Sharp I. D. , Haller E. E. , Dubon O. D. , Beeman J. W. , Yu K. M.
Published: June 2008

The electronic and magnetic effects of intentional compensation with nonmagnetic donors are investigated in the ferromagnetic semiconductors Ga1−xMnxAs and Ga1−xMnxP synthesized using ion implantation and pulsed-laser melting. It is demonstrated that compensation with nonmagnetic donors and MnI have similar qualitative effects on materials properties. With compensation TC decreases, resistivity increases, and stronger magnetoresistance and anomalous Hall effect attributed to skew scattering are observed. Ga1−xMnxAs can be controllably compensated with Te through a metal-insulator transition through which the magnetic and electrical properties vary continuously. The resistivity of insulating Ga1−xMnxAs:Te can be described by thermal activation to the mobility edge and simply activated hopping transport. Ga1−xMnxP doped with S is insulating at all compositions but shows decreasing TC with compensation. The existence of a ferromagnetic insulating state in Ga1−xMnxAs:Te and Ga1−xMnxP:S having TC’s of the same order as the uncompensated materials demonstrates that localized holes are effective at mediating global ferromagnetism in ferromagnetic semiconductors through the percolation of ferromagnetic “puddles” at low temperatures.
Spin dynamics triggered by subterahertz magnetic field pulses
Authors: Wang Zhao , Pietz Matthäus , Walowski Jakob , Förster Arno , Lepsa Mihail I. , Münzenberg Markus
Published: June 2008

Current pulses of up to 20 A and as short as 3 ps are generated by a low-temperature-grown GaAs photoconductive switch and guided through a coplanar waveguide, resulting in a 0.6 T subterahertz magnetic field pulse. The pulse length is directly calibrated using photocurrent autocorrelation. Magnetic excitations in Fe microstructures are studied by time-resolved Kerr spectroscopy. An ultrafast response time (within less than 10 ps of the magnetization) to the subterahertz electromagnetic field pulse is shown.
Observation of femtosecond carrier thermalization time in indium nitride
Authors: Sun Shih-Ze , Wen Yu-Chieh , Guol Shi-Hao , Lee Hong-Mao , Gwo Shangjr , Sun Chi-Kuang
Published: June 2008

Ultrafast carrier thermalization in n-type indium nitride (InN) with an electron concentration of 3.8×1018 cm−3 was investigated by femtosecond transient transmission measurements at room temperature with different wavelengths. An extremely fast carrier external thermalization time on the order of 400 fs was observed, which is much faster than all previous reports. This observed femtosecond thermalization time is consistent with a prediction based on a Coulomb screening effect. Through wavelength dependent and power dependent studies, even with a 400 fs thermalization time, we did not observe any evidence of the existence of the hot phonon effect, which agrees with a recent report that a longitudinal optical phonon lifetime could be shorter than 300 fs in specific InN samples.
Photoluminescence study of AgGaSe2, AgGa0.9In0.1Se2, and AgGa0.8In0.2Se2 crystals grown by the horizontal Bridgman technique
Authors: Cui Yunlong , Roy Utpal N. , Burger Arnold , Goldstein Jonathan T.
Published: June 2008

AgGaSe 2 , AgGa0.9In0.1Se2, and AgGa0.8In0.2Se2 single crystals grown by the horizontal Bridgman technique were investigated using photoluminescence (PL) at temperatures varied from 8 to 300 K. For the AgGaSe2 crystals, free exciton (FE), exciton bound to neutral donor (D0, X), and edge emissions including donor-acceptor pair (DAP) and free electron to neutral acceptor (e, A0) transitions were observed. Two donor levels with binding energies of 18 and 39 meV and two acceptor levels with 61 and 117 meV were observed. The FE peak positions of the AgGaSe2 were found to be blueshifted when the samples were illuminated with higher laser intensity. This behavior was more pronounced at higher temperature when the peaks were also significantly broadened. For the AgGa0.9In0.1Se2 crystals, three DAP emission peaks at 1.673, 1.570, and 1.545 eV were observed at 8 K. The excitonic peaks were not observed below 100 K because they were overshadowed by the 1.673 eV DAP emission. For the AgGa0.8In0.2Se2 crystal, the excitonic peak was barely resolved in the PL spectra at 9 K, and only two shallow defect levels were shown. The temperature coefficients of the band-gap energies of the crystals were measured. The thermal expansion effect of the AgGa0.8In0.2Se2 crystal was found to be much larger than that of AgGaSe2. The PL study showed that the AgGa0.8In0.2Se2 crystal had advantages over the AgGa0.9In0.1Se2 crystal for their use as potential radiation detectors.