bluuebunny/crossref_metadata_2025 huggingface dataset:
Snowmelt detection over the Greenland ice sheet from SSM/I brightness temperature daily variations
Authors: Tedesco Marco
Published: January 2007

We propose a technique for monitoring snowmelt over the Greenland ice sheet between 1992 and 2005 based on the difference between ascending and descending brightness temperatures (DAV) measured either at 19.35‐ or 37‐ GHz by the Special Sensor Microwave Imager (SSM/I). Wet snow is detected when both brightness temperatures and DAV values exceed fixed thresholds. Differently from existing techniques, a multi‐frequency approach allows detection of wet snow at different depths and intensities, providing a tool for improving climatological and hydrological applications. Air temperature values either recorded by ground based stations or derived from model are used for calibrating and validating the technique. Results are compared with those obtained using backscattering coefficients recorded by the NASA's Quick Scatterometer (QuikSCAT) during an extreme melting event occurring on June 2002. Long‐term results show that snowmelt extent has been increasing at a rate of ∼40,000 Km2 per year for the past 14 years.
Ionospheric plasma blobs observed by OI 630 nm all‐sky imaging in the Brazilian tropical sector during the major geomagnetic storm of April 6–7, 2000
Authors: Pimenta A. A. , Sahai Y. , Bittencourt J. A. , Rich F. J.
Published: January 2007

This paper presents first observations of plasma blobs (localized plasma density enhancements) associated with large‐scale plasma density depletions (plasma bubbles) in the nighttime low‐latitude F‐region during a major geomagnetic disturbance. Ground‐based observations of the OI 630 nm all‐sky images obtained at Cachoeira Paulista (22.7°S, 45.0°W), Brazil, in the Appleton anomaly region, showed the presence of plasma blobs during the major geomagnetic storm of April 6–7, 2000 (ΣKp = 38 −/40+; ∣Dst∣max = 288 nT). The OI 630 nm emission images were used to map the spatial and temporal locations of plasma blobs and bubbles in the bottomside of the F‐region. The F‐region parameters, presented in this work, were obtained from ionosondes operating near the same site and also at Sao Luis (2.6°S, 44.4°W), Brazil. Ionospheric plasma blobs and bubbles zonal drift velocities, measured by the all‐sky imaging system, showed that both the plasma blobs and the bubbles moved westward (normally the plasma drift is eastward during nighttime) on this magnetically disturbed night. Furthermore, the plasma blobs showed typically east‐west and north‐south extensions in the range of 110–160 km and 200–450 km, respectively. It appears that the DMSP‐15 satellite, orbiting at about 850 km altitude, passed through one of the blobs detected by the ground‐based observations on this night while crossing the Brazilian sector. This indicates the enormous altitude extent [from about 275 km (OI 630.0 nm emission) to 850 km (DMSP satellite) altitude] of the localized plasma density enhanced regions. In this work, we present and discuss several features related to the dynamics of the localized plasma density enhancements and large‐scale plasma density depletions during this major geomagnetic disturbance.
Magnetic conjugate observation of the F3 layer using the SEALION ionosonde network
Authors: Uemoto Jyunpei , Ono Takayuki , Maruyama Takashi , Saito Susumu , Iizima Masahide , Kumamoto Atsushi
Published: January 2007

Results from the meridional ionosonde network located in Southeast Asia (SEALION) demonstrate the interesting nature of the F3 layer, showing its generation mechanism. Ionograms obtained on 16 November 2004 and 31 March 2005 at Chiang Mai (CMU; geographic latitude 18.8°N, geographic longitude 98.9°E, and magnetic latitude 13.2°N), Chumphon (CPN; 10.7°N, 99.4°E, and 3.2°N) and Kototabang (KTB; 0.2°S, 100.3°E, and 10.1°S) showed significant differences between CPN near the magnetic equator, and CMU and KTB in the magnetic low‐latitude region. The simultaneous magnetic conjugate observations of the F3 layer achieved using the SEALION ionosonde network data showed clear dependences of the F3 layer on the magnetic latitude. It is suggested that these magnetic latitude dependences of the F3 layer can be explained by considering the plasma diffusion effects along the magnetic field lines in the magnetic low‐latitude region.
Alkyl nitrate (C1‐C3) depth profiles in the tropical Pacific Ocean
Authors: Dahl E. E. , Yvon‐Lewis S. A. , Saltzman E. S.
Published: January 2007

This paper reports the first depth profile measurements of methyl, ethyl, isopropyl and n‐propyl nitrates in the tropical Pacific Ocean. Depth profile measurements were made at 22 stations during the Project Halocarbon Air Sea Exchange cruise, in warm pool, equatorial, subequatorial, and gyre waters. The highest concentrations, up to several hundred pM of methyl nitrate, were observed in the central Pacific within 8 degrees of the equator. In general, alkyl nitrate levels were highest in the surface mixed layer, and decreased with depth below the mixed layer. The spatial distribution of the alkyl nitrates suggests that there is a strong source associated with biologically productive ocean regions, that is characterized by high ratios of methyl:ethyl nitrate. However, the data do not allow discrimination between direct biological emissions and photochemistry as production mechanisms. Alkyl nitrates were consistently detectable at several hundred meters depth. On the basis of the estimated chemical loss rate of these compounds, we conclude that deep water alkyl nitrates must be produced in situ. Possible sources include free radical processes initiated by radioactive decay or cosmic rays, enzymatically mediated reactions involving bacteria, or unidentified chemical mechanisms involving dissolved organic matter.
Summertime carbonaceous aerosols collected in the marine boundary layer of the Arctic Ocean
Authors: Xie Zhouqing , Blum Joel D. , Utsunomiya Satoshi , Ewing R. C. , Wang Xinming , Sun Liguang
Published: January 2007

The chemistry, morphology, and microscale to nanoscale structures of carbonaceous aerosols from the marine boundary layer of the Arctic Ocean were investigated by a variety of electron microscopy techniques, including scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), and energy‐dispersive X‐ray spectroscopy (EDS). The relative levels of particles of black carbon (BC) were determined by electron paramagnetic resonance (EPR). Polycyclic aromatic hydrocarbons (PAHs) absorbed onto BC particles were extracted by the soxhlet extraction method and analyzed by gas chromatography mass spectrometry (GC‐MS). The results show that the dominant particles of BC are char particles with spherical shape, porous structure, and high sulfur content, which are typically derived from residual oil combustion on ships. The spatial distribution of BC from ship emissions was found to be concentrated around the periphery of the Arctic Ocean, suggesting relatively intensive contamination by ships in the Russian and Canadian Arctic. The abundance of PAHs on BC particles ranges from 142 to 2672 pg/m3 (mean = 702 pg/m3), which is significantly higher than values previously measured by land‐based observation. Thus we find that ship emissions are a potentially important contributor to the PAH levels at some locations in the Arctic Ocean during the summer.
Long‐term observations of Schumann resonances at Modra Observatory
Authors: Ondrášková A. , Kostecký P. , Ševčík S. , Rosenberg L.
Published: January 2007

The paper presents a summary of more than 4 years of continuous Schumann resonance (SR) monitoring of the vertical electric component at Modra Observatory. Principal parameters (peak frequency, amplitude, and quality factor) are determined for four resonances from 7 to 30 Hz, i.e., for modes one through four. Attention is also given to the less frequently compiled mode four. The resonance parameters are computed from 48 daily measurements and are represented as the mean monthly values for each time of the detection. Fitting of spectral peaks by Lorentz function is the main method used in data postprocessing. Diurnal, seasonal variations and the indication of interannual variations of these parameters (especially peak frequency) are discussed. The results are compared with other observatory measurements. Our observations confirm that variations in peak frequency of the lower‐SR modes can be attributed mainly to the source‐observer distance effect.
Analysis of Q burst waveforms
Authors: Ogawa Toshio , Komatsu Masayuki
Published: January 2007

The electric field changes in ELF to VLF were observed with a ball antenna in fair weather at Kochi (latitude 33.3°N, longitude 133.4°E) during 2003–2004. Some 376 Q bursts were obtained, seven examples of which are analyzed in the present study. The continuous frequency spectra of the Q bursts and the background noises from 1.0 Hz to 11 kHz are compared, and it was found that the Q bursts prevail over the background in the frequency range from 1 to 300 Hz. The surplus is 20 dB (in amplitude) near the fundamental mode frequency. The “W”‐type changes found in the initial portion of the Q burst waveforms are interpreted as the combined electromagnetic waveform of direct and antipodal waves from the causative lightning strokes. From the time intervals between the two waves, the source‐receiver distances are estimated as far as 19 Mm. The pulses to excite the Schumann resonances in the Q bursts are clearly identified.
Challenges to macromolecular drug delivery
Authors: Juliano R.
Published: January 2007

The use of macromolecules, particularly monoclonal antibodies, as therapeutic agents has come to the forefront in recent years. The biodistribution and delivery issues for protein drugs are shared to a substantial degree with other emerging therapeutic approaches including pharmacologically active nucleic acids and nanoparticles. A generalized approach to these issues involves consideration of the multiple biological barriers that stand between the macromolecular drug or nanoparticle at its site of administration and its ultimate biological target. Considerations of size, stability, non-specific versus specific associations and potency versus toxicity all play a role. The creation of delivery approaches that combine high specificity for the target cell or tissue, high therapeutic payload and modest toxicity remains a challenge, although some very promising examples have emerged recently. A variety of sophisticated targeting strategies, based primarily on combinatorial library methods, when used in combination with new technologies to identify cell-surface receptor ‘signatures’ of specific tissues, will facilitate advances in targeted delivery of macromolecules and nanoparticles. The challenges to contemporary macromolecule drug delivery are complex, thus new research paradigms are emerging that combine the talents of physical and biological scientists to address this key issue for modern pharmacology and therapeutics.
A non-covalent peptide-based strategy for siRNA delivery
Authors: Crombez L. , Charnet A. , Morris M.C. , Aldrian-Herrada G. , Heitz F. , Divita G.
Published: January 2007

The major obstacle to clinical development of siRNAs (short interfering RNAs), like for most of the nucleic-acid-based strategies, is their poor cellular uptake and bioavailability. Although several viral and non-viral strategies have been proposed to improve siRNA delivery, their applications in vivo remain a major challenge. We have developed a new strategy, based on a short amphipathic peptide, MPG, that is able to form stable nanoparticles with siRNA. MPG-based particles enter the cell independently of the endosomal pathway and can efficiently deliver siRNA in a fully biologically active form into a variety of cell lines and in vivo. This short review will discuss the mechanism and the potency of the MPG strategy for siRNA delivery both in vitro and in vivo.
Combinatorial selection and delivery of thioaptamers
Authors: Thiviyanathan V. , Somasunderam A.D. , Gorenstein D.G.
Published: January 2007

Oligonucleotide-based agents are emerging as potential therapeutic agents that can be attractive alternatives for the small-molecule chemical drugs. Monothiophosphate-backbone-modified DNA aptamers (thioaptamers) that specifically and tightly bind to the RNase H domain of the HIV RT (reverse transcriptase) have been isolated from nucleic acid libraries using combinatorial selection methods. The selected thioaptamer inhibited RNase H activity of the HIV RT in in vitro studies. In cell cultures, the transfected thioaptamer markedly reduced HIV production in a dose-dependent manner. Gel electrophoretic mobility-shift assays and NMR spectroscopy showed that the selected thioaptamer binds to the isolated RNase H domain, but did not bind to a structurally similar RNase H from Escherichia coli. In cell cultures, the transfected thioaptamer showed a dose-dependent inhibition of HIV replication, with a maximal inhibition of 83%. Using various liposome-delivery agents, the DNA thioaptamer was transfected into HIV-infected astrocytoma adherent cells with greater than 70% efficiency.
Designing polymer conjugates as lysosomotropic nanomedicines
Authors: Duncan R.
Published: January 2007

Marriage of cell biology (the concept of ‘lysosomotropic drug delivery’) and the realization that water-soluble synthetic polymers might provide an ideal platform for targeted drug delivery led to the first synthetic polymer–drug conjugates that entered clinical trials as anticancer agents. Conceptually, polymer conjugates share many features with other macromolecular drugs, but they have the added advantage of the versatility of synthetic chemistry that allows tailoring of molecular mass and addition of biomimetic features. Conjugate characteristics must be optimized carefully to ensure that the polymeric carrier is biocompatible and that the polymer molecular mass enables tumour-selective targeting followed by endocytic internalization. The polymer–drug linker must be stable in transit, but be degraded at an optimal rate intracellularly to liberate active drug. Our early studies designed two HPMA [N-(2-hydroxypropyl)methacrylamide] copolymer conjugates containing doxorubicin that became the first synthetic polymer–drug conjugates to be tested in phase I/II clinical trials. Since, a further four HPMA copolymer–anticancer drug conjugates (most recently polymer platinates) and the first polymer-based γ-camera imaging agents followed. Polymer–drug linkers cleaved by lysosomal thiol-dependent proteases and the reduced pH of endosomes and lysosomes have been used widely to facilitate drug liberation. It is becoming clear that inappropriate trafficking and/or malfunction of enzymatic activation can lead to new mechanisms of clinical resistance. Recent studies have described HPMA copolymer conjugates carrying a combination of both endocrine and chemotherapy that are markedly more active than individual conjugates carrying a single drug. Moreover, current research is investigating novel dendritic polymer architectures and novel biodegradable polymers as drug carriers that will provide improved drug delivery and imaging probes in the future. The present paper reviews the clinical status of polymeric anticancer agents, the rationale for the design of polymer therapeutics and discusses the benefits and challenges of lysosomotropic delivery.
The TRP channel superfamily: insights into how structure, protein–lipid interactions and localization influence function
Authors: Reaves B.J. , Wolstenholme A.J.
Published: January 2007

TRP (transient receptor potential) cationic channels are key molecules that are involved in a variety of diverse biological processes ranging from fertility to osmosensation and nociception. Increasing our knowledge of these channels will help us to understand a range of physiological and pathogenic processes, as well as highlighting potential therapeutic drug targets. The founding members of the TRP family, Drosophila TRP and TRPL (TRP-like) proteins, were identified within the last two decades and there has been a subsequent explosion in the number and type of TRP channel described. Although information is accumulating as to the function of some of the TRP channels, the activation and inactivation mechanisms, structure, and interacting proteins of many, if not most, are awaiting elucidation. The Cell and Molecular Biology of TRP Channels Meeting held at the University of Bath included speakers working on a number of the different subfamilies of TRP channels and provided a basis for highlighting both similarities and differences between these groups. As the TRP channels mediate diverse functions, this meeting also brought together an audience with wide-ranging research interests, including biochemistry, cell biology, physiology and neuroscience, and inspired lively discussion on the issues reviewed herein.
Subunit interaction in channel assembly and functional regulation of transient receptor potential melastatin (TRPM) channels
Authors: Jiang L.-H.
Published: January 2007

Functional TRPM (transient receptor potential melastatin) ion channels are multimers, thought to be tetramers. Subunit interaction is the prerequisite step in channel assembly, and the specificity of subunit interaction is crucial in assembling channels with distinct functional properties. In addition, expression of short non-functional subunits and their interaction with full-length subunits serve as one of the post-translational mechanisms regulating the channel activity. This paper aims to provide an overview of the current knowledge of TRPM subunit interactions and their roles in assembly and functional regulation of the TRPM channels.
TRP channels activated by extracellular hypo-osmoticity in epithelia
Authors: Harteneck C. , Reiter B.
Published: January 2007

TRP (transient receptor potential) channels comprise a superfamily of non-selective cation channels with at least seven subfamilies. The variety of subfamilies corresponds to the differences in the activation mechanisms and functions. TRPM3 (TRP melastatin 3) and TRPV4 (TRP vanilloid 3) have been characterized as cation channels activated by extracellular hypo-osmoticity. In addition, TRPV4 is activated by metabolites of arachidonic acid as well as α-isomers of phorbol esters known to be ineffective in stimulating proteins of the protein kinase C family. TRPM3 is responsive to sphingosine derivatives. The detection of splice variants with probably different activation mechanisms supports the idea that TRPM3 may have diverse cellular functions depending on the expression of a particular variant. The expression of TRPV4 in many epithelial cell types raised the question of the role of TRPV4 in epithelial physiology. Single-cell experiments as well as approaches using epithelial layers show that multiple cellular responses are triggered by TRPV4 activation and subsequent elevation of intracellular calcium. The TRPV4-induced responses increasing transcellular ion flux as well as paracellular permeability may allow the cells to adjust to changes in extracellular osmolarity. In summary, TRPV4 plays a central role in epithelial homoeostasis by modulating epithelial barrier function.
Bipolar phospholipid sensing by TRPC5 calcium channel
Authors: Beech D.J.
Published: January 2007

TRPC5 [TRP (transient receptor potential) canonical (or classical) 5] is a widely expressed mammalian homologue of Drosophila TRP, forming a calcium- and sodium-permeable channel in the plasma membrane either as a homomultimer or heteromultimer with other proteins (e.g. TRPC1). Although several factors are known to stimulate the channel, understanding of its endogenous activators and functions is limited. This paper provides a brief and focused review of our latest findings that show that TRPC5 is a sensor of important signalling phospholipids, including lysophosphatidylcholine and sphingosine 1-phosphate, acting extracellularly or intracellularly. Underlying mechanisms of action and biological relevance are discussed.
Concerted action of associated proteins in the regulation of TRPV5 and TRPV6
Authors: Schoeber J.P.H. , Hoenderop J.G.J. , Bindels R.J.M.
Published: January 2007

Ca2+ is an essential ion in all organisms and many physiological functions in the body rely on the exact maintenance of the Ca2+ balance. The epithelial Ca2+ channels TRPV5 [TRP (transient receptor potential) vanilloid 5] and TRPV6 are the most Ca2+-selective members of the TRP superfamily and are generally considered as the gatekeepers of Ca2+ entry across epithelia. TRPV5 is involved in Ca2+ reabsorption from pro-urine, while TRPV6 has an essential role in intestinal Ca2+ uptake. These channels are the prime targets of calciotropic hormonal regulation, including vitamin D and parathyroid hormone. In addition, extra- and intra-cellular signalling by associated proteins and Ca2+ itself play key roles in TRPV5 and TRPV6 regulation. In this paper, we describe the present understanding of the concerted action of calbindin-D28k, klotho and BSPRY (B-box and SPRY-domain-containing protein) at different levels throughout the epithelial cell to control Ca2+ influx at the luminal entry gate.
Differential role of TRP channels in prostate cancer
Authors: Prevarskaya N. , Flourakis M. , Bidaux G. , Thebault S. , Skryma R.
Published: January 2007

A major clinical problem with PC (prostate cancer) is the cell's ability to survive and proliferate upon androgen withdrawal. Indeed, deregulated cell differentiation and proliferation, together with the suppression of apoptosis, provides the condition for abnormal tissue growth. Here, we examine the differential role of TRP (transient receptor potential) channels in the control of Ca2+ homoeostasis and growth of PC cells.
Plasmodesmata and intercellular transport of viral RNA
Authors: Hofmann C. , Sambade A. , Heinlein M.
Published: January 2007

Cell-to-cell communication in plants involves the symplastic trafficking of informational protein and RNA macromolecules through cytoplasmic bridges in the plant cell wall known as plasmodesmata. Viruses exploit this route for the spread of infection and are used as a model to study the mechanisms by which macromolecules are targeted to the pore. Studies using tobacco mosaic virus have led to the identification of host components that participate in plasmodesmal targeting of viral RNA and movement protein.
Epidermal pattern formation in the root and shoot of Arabidopsis
Authors: Schellmann S. , Hülskamp M. , Uhrig J.
Published: January 2007

Root hair formation, stomata development on hypocotyls and trichome formation on leaves in Arabidopsis represent three model systems for epidermal patterning in plants that involve a common set of genes or corresponding homologues. The resulting pattern and the developmental readout are, however, strikingly different. Trichomes become regularly spaced on the leaf surface. Root hairs and stomata-bearing cells are formed in rows at specific locations with reference to the underlying cortex cells. In this review, we summarize the mechanistic similarities and discuss differences that might account for the different outcome of patterning in each system.
Reprogramming of root epidermal cells in response to nutrient deficiency
Authors: Perry P. , Linke B. , Schmidt W.
Published: January 2007

Post-embryonic development of the root system is highly plastic to environmental cues, compensating for the sessile lifestyle of plants. The fate of epidermal cells of Arabidopsis roots is particularly responsive to nutritional signals, leading to an increase in the root's surface area in the absence of the essential but immobile minerals iron, phosphate and manganese. The resulting phenotype is characteristic of the respective condition. Growth under nutrient starvation affects the expression of genes involved in cell specification, indicating that environmental signals are perceived at an early stage of cell development. Cell fate decisions are controlled at different levels, probably integrated at the level of chromatin organization.
To quantum averages through asymptotic expansion of classical averages on infinite-dimensional space
Authors: Khrennikov Andrei
Published: January 2007

We study asymptotic expansions of Gaussian integrals of analytic functionals on infinite-dimensional spaces (Hilbert and nuclear Frechet). We obtain an asymptotic equality coupling the Gaussian integral and the trace of the composition of scaling of the covariation operator of a Gaussian measure and the second (Frechet) derivative of a functional. In this way we couple classical average (given by an infinite-dimensional Gaussian integral) and quantum average (given by the von Neumann trace formula). We can interpret this mathematical construction as a procedure of “dequantization” of quantum mechanics. We represent quantum mechanics as an asymptotic projection of classical statistical mechanics with infinite-dimensional phase space. This space can be represented as the space of classical fields, so quantum mechanics is represented as a projection of “prequantum classical statistical field theory.”
Detection of hydrogen at localized regions by unoccupied electronic states in iron carbides: Towards high spatial resolution mapping of hydrogen distributions
Authors: Tatsumi Kazuyoshi , Muto Shunsuke , Yoshida Tomoko
Published: January 2007

We have shown in a previous study [S. Muto et al., Jpn. J. Appl. Phys., 44, 2061 (2005)] that a high hydrogen storage capacity in hydrogenated nanostructured graphite is partly ascribable to the formation of hydrogenated iron carbide particles. In the present study, we examined the effects of hydrogen on electron energy-loss and x-ray absorption spectra of the iron carbides. The experimentally obtained spectral changes were interpreted on the basis of first principles calculations for a model structure of the Fe–C–H system. Finally, we demonstrate high spatial resolution imaging of hydrogen distributions in iron-carbon systems by an energy-filtering transmission electron microscopy technique, utilizing the present spectral changes associated with hydrogen incorporation.
Dynamical behavior for the three-dimensional generalized Hasegawa-Mima equations
Authors: Zhang Ruifeng , Guo Boling
Published: January 2007

The long time behavior of solution of the three-dimensional generalized Hasegawa-Mima [Phys. Fluids 21, 87 (1978)] equations with dissipation term is considered. The global attractor problem of the three-dimensional generalized Hasegawa-Mima equations with periodic boundary condition was studied. Applying the method of uniform a priori estimates, the existence of global attractor of this problem was proven, and also the dimensions of the global attractor are estimated.
Note on Z2 symmetries of the Knizhnik-Zamolodchikov equation
Authors: Giribet Gaston E.
Published: January 2007

We continue the study of hidden Z2 symmetries of the four-point sl(2)̂k Knizhnik-Zamolodchikov equation initiated by Giribet [Phys. Lett. B 628, 148 (2005)]. Here, we focus our attention on the four-point correlation function in those cases where one spectral flowed state of the sector ω=1 is involved. We give a formula that shows how this observable can be expressed in terms of the four-point function of non spectral flowed states. This means that the formula holding for the winding violating four-string scattering processes in AdS3 has a simple expression in terms of the one for the conservative case, generalizing what is known for the case of three-point functions, where the violating and the nonviolating structure constants turn out to be connected one to each other in a similar way. What makes this connection particularly simple is the fact that, unlike what one would naively expect, it is not necessary to explicitly solve the five-point function containing a single spectral flow operator to this end. Instead, nondiagonal functional relations between different solutions of the Knizhnik-Zamolodchikov equation turn out to be the key point for this short path to exist. Considering such functional relation is necessary but it is not sufficient; besides, the formula also follows from the relation existing between correlators in both Wess-Zumino-Novikov-Witten (WZNW) and Liouville conformal theories.
Frequency response of solid-state impact ionization multipliers
Authors: Beutler Joshua L. , Clauss Carleton S. , Johnson Michael S. , Hawkins Aaron R. , Jack Mike D. , Chapman George R. , Kosai Ken
Published: January 2007

A study of the frequency response of solid-state impact ionization multipliers (SIMs) is presented that emphasizes the role of resistive and capacitive elements of the device to establish response limitations. SIMs are designed to amplify input currents from an external source through the impact ionization mechanism. An equivalent circuit model for the SIM is developed based on its current versus voltage characteristics, which is used to derive a frequency response model. Theoretical frequency response matches very closely to measured responses for first generation SIM devices constructed on p-type silicon epitaxial layers with nickel silicide Schottky contact injection points. Devices were measured using a photodiode as a current source under light intensities between 74nA and 7.4μA. These SIMs were shown to have a low frequency response that follows a KT∕I relationship. Using an external photodiode with an effective capacitance of 6.8pF, frequency response for a 1.8μA input current was limited to 100kHz. A large effective barrier resistance due to the Schottky contact and 12kΩ space charge resistance dependent on device geometry dominate the response. Future SIM designs with higher frequency response will have to significantly lower both the input barrier resistance and space charge resistance.
Macroscopic uncertainty of the effective properties of random media and polycrystals
Authors: Chinh Pham Duc
Published: January 2007

The concept of macroscopic properties (conductivity, elasticity,...) of heterogeneous media is reexamined and defined, with the assessment that the effective properties of randomly inhomogeneous materials (in the large representative volume element limit) generally are not unique, but scatter within some uncertainty limits; hence, the statistical homogeneity, statistical isotropy, and ergodicity hypotheses often attributed to them may be considered only as approximations, and random irregular systems may not have definite percolation thresholds. Our formal bounds on the elastic moduli of random polycrystals are used to derive explicit estimates of the uncertainty of the moduli with numerical results for the aggregates of hexagonal and tetragonal crystals of all classes. The results indicate that the macroscopic moduli of many polycrystalline materials are determined within just two or three significant digits—similar to the respective results for the conductivity properties.
Raman scattering characterization and electron phonon coupling strength for MeV implanted InP(111)
Authors: Paramanik Dipak , Varma Shikha
Published: January 2007

Structural modifications in InP(111) due to 1.5 MeV implantation of Sb have been characterized using first-order and second-order Raman spectroscopy. With both longitudinal optical (LO) and transverse optical (TO) modes allowed for InP(111), we have investigated the evolution of both these modes as a function of fluence. Investigations of both the first and second-order Raman modes indicate the presence of tensile stress in the lattice after implantation, which increases with fluence. Results show a coexistence of nanocrystalline InP regions and amorphous zones in the lattice. Consequently phonon confinement is observed and phonon confinement model (PCM) has been applied here to estimate the coherence length and the size of nanocrystalline zones in InP lattice after implantation. Nanocrystalline zones as small as 35 Å have been observed here. A LO phonon-plasmon coupled mode, due to the charge layer in the vicinity of the surface, has also been observed. This coupled mode becomes sharper and more intense with increasing fluence. For high fluences, crystalline to amorphous phase transition has also been observed. First and second-order LO modes have been utilized to estimate the electron-phonon coupling strengths. The coupling strength is observed to decrease as the nanocrystalline zones, in the implanted lattice, become smaller.
Investigation of the mesoscopic scale response of low-density pressings of granular sugar under impact
Authors: Trott Wayne M. , Baer Melvin R. , Castañeda Jaime N. , Chhabildas Lalit C. , Asay James R.
Published: January 2007

The mesoscopic scale response of low-density pressings of granular sugar (sucrose) to shock loading has been examined in gas-gun impact experiments using both VISAR and a line-imaging, optically recording velocity interferometer system in combination with large-volume-element, high-resolution, three-dimensional numerical simulations of these tests. Time-resolved and spatially resolved measurements of material motion in waves transmitted by these pressings have been made as a function of impact velocity, sample thickness, and sample particle size distribution. Observed wave profiles exhibit a precursor regime arising from elastic stress wave propagation and a dispersive compaction wave with superimposed localized particle velocity fluctuations of varying amplitude. Material motion associated with dynamic stress bridging leads compaction wave arrival by ∼2μs at the lowest impact velocity (0.25kms−1) employed in this study and <200ns at the higher values (0.7–0.8kms−1). Over the same range, the compaction wave becomes markedly less dispersive with wave ramp durations declining from ∼500to∼50ns. For impact velocities near 0.5kms−1 and samples varying in thickness from 2.27to8.03mm, a roughly steady wave behavior is obtained at the thinner end of the range; however, evidence of subtle wave evolution is apparent over this thickness range. Pressings of sieved sugar with different particle size distributions exhibit distinguishable differences in stress bridging and compaction wave behavior. These pressings somewhat limit stochastic behavior and provide favorable conditions for the development of quasiperiodic fluctuations in particle velocity, particularly in impacts generating incomplete compaction. The experimental results are consistent with the exceedingly complex wave field behavior evident in the numerical simulations and provide useful benchmark wave profiles (at the sample boundary) for validation of material models used in these calculations.
Effect of injection current on the repeatability of laser diode junction voltage-temperature measurements
Authors: Kirkup L. , Kalceff W. , McCredie G.
Published: January 2007

The junction-voltage temperature relationship of a laser diode is used to determine the temperature of the device in the range −20 to 120 °C. We consider changes that occur to this relationship when the diode is driven at its nominal operating current and above. It is found that estimates of the parameters that appear in a function fitted to the voltage-temperature data are sensitive to driving currents at and above the nominal operating current. Changes in parameter estimates are attributed to degradation due to surface recombination at facets occurring when the laser diode is overdriven. An indication of this degradation is the change in the ideality factor that occurs as the current to the device is raised. This work indicates that the temperature of the junction can be determined over the range −20 to 120 °C with a standard uncertainty of ≈0.5 °C.
Structural and optical properties of low-density and In-rich InAs∕GaAs quantum dots
Authors: Alloing B. , Zinoni C. , Li L. H. , Fiore A. , Patriarche G.
Published: January 2007

Self-assembled InAs∕GaAs quantum dots have been grown at very low InAs growth rate in order to form sparse and large quantum dots (QDs) emitting in the near infrared (1300–1400nm), for application as single-photon sources. The structural and optical properties of these QDs as a function of the growth rate were systematically investigated. The QDs grown at the lowest rate (∼10−3ML∕s) present a very low dot density (∼2×108dots∕cm2), high In content, and good size homogeneity. Photoluminescence and time-resolved photoluminescence measurements performed at different powers and temperatures provide information on their luminescence efficiency, and on the recombination processes occurring in the low-density QDs as compared to higher densities.
Thermal activation of excitons in asymmetric InAs dots-in-a-well InxGa1−xAs∕GaAs structures
Authors: Torchynska T. V. , Casas Espinola J. L. , Borkovska L. V. , Ostapenko S. , Dybiec M. , Polupan O. , Korsunska N. O. , Stintz A. , Eliseev P. G. , Malloy K. J.
Published: January 2007

Photoluminescence, its temperature dependence, and photoluminescence excitation spectra of InAs quantum dots embedded in asymmetric InxGa1−xAs∕GaAs quantum wells [dots in a well (DWELL)] have been investigated as a function of the indium content x (x=0.10–0.25) in the capping InxGa1−xAs layer. The asymmetric DWELL structures were created with the aim to investigate the influence of different barrier values at the quantum dot (QD)/quantum well interface on the photoluminescence thermal quenching process. The set of rate equations for the two stage model for the capture and thermal escape of excitons in QDs are solved to analyze the nature of thermal activation energies for the QD photoluminescence quenching process. The two stage model for exciton thermal activation was confirmed experimentally in the investigated QD structures as well. The localization of nonradiative defects in InAs∕InGaAs DWELL structures is discussed on the base of comparison of theoretical and numerically calculated (fitting) results.
On positive charge formed under negative bias temperature stress
Authors: Chang M. H. , Zhang J. F.
Published: January 2007

As nitrogen concentration in silicon oxynitride (SiON) increases, negative bias temperature instability (NBTI) becomes a limiting factor for device lifetime. Despite recent efforts, there are confusions and issues remaining unsolved. One of them being how important positive charge formation in SiON is for NBTI and whether all positive charges are the same type. The objective of this work is to investigate positive charge formed in SiON during negative bias temperature stress (NBTS). In comparison with the positive charge formed during substrate hole injection where interface state generation is negligible, it will be shown that NBTS can induce three different types of positive charges: as-grown hole trapping, antineutralization positive charge (ANPC), and cyclic positive charge. Efforts have been made to search for the feature of NBTI, which cannot be explained without involving positive charge. It is unambiguously identified that the impact of measurement temperature on NBTI originates from only one type of defect: ANPC. By using the “on-the-fly” measurement technique, the positive charge density observed in a 2.7nm SiON can reach to the upper half of 1012cm−2, which is comparable with the positive charge reported for relatively thick SiO2 (>5nm). The relative importance of positive charge formation depends on measurement interruption time. The shorter the interruption, the more important positive charge becomes for NBTI.
Stability of silicon-doped C60 dimers
Authors: Marcos Pedro A. , Alonso Julio A. , López María J.
Published: January 2007

A theoretical investigation on the structure, stability, and thermal behaviors of the smallest polymeric units, the dimers, formed from substitutionally Si-doped fullerenes is presented. A density functional based nonorthogonal tight-binding model has been employed for describing the interatomic interactions. The study focuses on those polymeric structures which involve Si–Si or Si–C interfullerene bonds. The binding energy of the dimers increases with their Si content from about 0.25eV in C60–C60 to about 4.5eV in C58Si2–C58Si2. Moreover, the C59SiC59 dimer, linked through the sharing of the Si atom between the two fullerenes, has been also considered. Upon heating, the dimers eventually fragment into their constituent fullerene units. The fragmentation temperature correlates with the strength of the interfullerene bonds. C58Si2–C58Si2 exhibits a higher thermal stability (fragmentation temperature of ∼500K) than the pure carbon C60–C60 dimer (with a fragmentation temperature of ∼325K). Given the higher structural and thermal stabilities of the Si-doped fullerene dimers, the authors propose the use of substitutionally Si-doped fullerenes as the basic units for constructing new fullerene-based polymers.
Colloidal dynamics near a wall studied by evanescent wave light scattering: Experimental and theoretical improvements and methodological limitations
Authors: Holmqvist Peter , Dhont Jan K. G. , Lang Peter R.
Published: January 2007

The dynamics of colloidal spheres near to a wall is studied with an evanescent wave scattering setup that allows for an independent variation of the components of the scattering wave vector normal and parallel to the wall. The correlation functions obtained with this novel instrumentation are interpreted on the basis of an expression for their short time behavior that includes hydrodynamic interactions between the colloidal spheres and the wall. The combination of the evanescent wave scattering setup and the exact expression for the short time behavior of correlation functions allows for an unambiguous measurement of the particle mobility parallel and normal to the wall by means of light scattering. It is possible to measure the viscous wall drag effect on the dynamics of particles with radii as small as 27nm, where, however, the method reaches its limits due to the low scattering intensities of such small particles.
A common, avoidable source of error in molecular dynamics integrators
Authors: Lippert Ross A. , Bowers Kevin J. , Dror Ron O. , Eastwood Michael P. , Gregersen Brent A. , Klepeis John L. , Kolossvary Istvan , Shaw David E.
Published: January 2007

In constrained molecular dynamics simulations using some of the most popular molecular dynamics codes, calculation of the velocities of constrained particles is based solely on the differences in particle positions during two successive time steps. This creates a numerical instability that the authors’ show to be signicant in a typical single-precision floating-point simulation. They describe a simple modification that eliminates this source of instability and demonstrate that this change substantially reduces the energy drift of a sample single-precision NVE simulation.
Conformational dependence of intramolecular vibrational redistribution in methanol
Authors: Maksyutenko Pavel , Boyarkin Oleg V. , Rizzo Thomas R. , Perry David S.
Published: January 2007

Previous state-selected spectra of methanol in the 5ν1 OH stretch overtone region [O. V. Boyarkin, T. R. Rizzo, and D. S. Perry, J. Chem. Phys. 110, 11346 (1999)] revealed a structure indicating an intramolecular vibrational redistribution on three time scales. Whereas in that work, methanol in the 5ν1 bright state was prepared close to the staggered conformation, methanol in the “partially eclipsed” conformation is prepared here by double resonance excitation through a torsionally excited intermediate state. The excited molecules are detected by infrared laser assisted photofragment spectroscopy. In partially eclipsed methanol, the strong coupling of the ν1 OH stretch to the ν2 CH stretch becomes weaker, but the coupling responsible for the widths of the narrowest features becomes stronger.
London dispersion forces by range-separated hybrid density functional with second order perturbational corrections: The case of rare gas complexes
Authors: Gerber I. C. , Ángyán J. G.
Published: January 2007

A satisfactory account of the van der Waals (vdW) (London dispersion) forces is, in general not possible by the Kohn-Sham method using standard local, semilocal generalized gradient approximation (GGA), or meta-GGA density functionals. The recently proposed range-separated hybrid (RSH) approach, supplemented by second order perturbational corrections (MP2) to include long-range dynamic correlation effects, offers a physically consistent, seamless description of dispersion forces. It is based on a rigorous generalization of the Kohn-Sham method, where long-range exchange and correlation effects are treated by wave function methods, while short-range electron exchange and correlation are handled by local or semilocal functionals. The method is tested on a series of rare gas dimers in comparison with standard wave function theory and density functional theory approaches. In contrast to the most successful exchange correlation functionals, which describe at best the vdW minimum, the RSH+MP2 approach is valid also in the asymptotic region and the potential curve displays the correct 1∕R6 behavior at large internuclear separations. In contrast to usual MP2 calculations, the basis set superposition error is considerably reduced, making RSH+MP2 an ideal tool for exploring the potential energy surface of weakly bound molecular complexes.
The vibrational structure of the X̃A11−ÃB11 and ÃB11−B̃A11 band systems of GeH2∕GeD2 based on global potential energy surfaces
Authors: Tokue Ikuo , Ebina Shingo , Kanai Megumi , Nanbu Shinkoh
Published: January 2007

Transition probabilities were evaluated for the X̃A11−ÃB11 and ÃB11−B̃A11 systems of GeH2 and GeD2 to analyze the X̃→Ã→B̃ photoexcitation. Franck-Condon factors (FCFs) and Einstein’s B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the X̃A11, ÃB11, and B̃A11 electronic states and the transition dipole moments for the X̃−Ã and Ã−B̃ systems. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least squares method combined with the Shepard [Proceedings of the 1968 23rd ACM National Conference (ACM, New York, 1968)] interpolation. The barriers to linearity correcting the spin-orbit interaction are evaluated to be 22000cm−1 for the X̃ state, 6300cm−1 for the Ã state, and 560cm−1 for the B̃ state. The obtained FCFs for the X̃−Ã and Ã−B̃ systems indicate that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies within the three states. The photoexcitation and fluorescence spectra calculated for the X̃−Ã system agree well with the observed spectra. The theoretical lifetimes for lower vibrational levels of the Ã and B̃ states were calculated from the fluorescence decay rates for the Ã−X̃, B̃−Ã, and B̃−X̃ emissions, and the lifetimes for the Ã state are in good agreement with the observed values except those affected by predissociation.
Behavior of Si and C atoms in ion amorphized SiC
Authors: Jiang W. , Zhang Y. , Engelhard M. H. , Weber W. J. , Exarhos G. J. , Lian J. , Ewing R. C.
Published: January 2007

Single crystal 6H-SiC wafers were fully amorphized at room temperature or 200K using 1.0 or 2.0MeV Au+ ion irradiation. The thickness of the amorphized layers has been determined using Rutherford backscattering spectrometry under ion channeling conditions. Microstructures of the irradiated SiC have been examined using cross-sectional transmission electron microscopy. The depth profiles of both the Si and C atoms have been studied using both x-ray photoelectron spectroscopy (XPS) and time-of-flight energy elastic recoil detection analysis. Neither Si nor C in the amorphized SiC exhibits a significant mass transport by diffusion during the irradiation and subsequent storage at room temperature. There is no observable phase segregation of either Si or C in the amorphized SiC. Ar+ ion sputtering leads to modifications of the composition, structure, and chemical bonding at the 6H-SiC surface. The Si–Si bonds at the sputtered surface (amorphized) do not appear, as suggested by the XPS; however, Raman backscattering data reveal the existence of the Si–Si bonds in the bulk amorphized SiC, in addition to the C–C and Si–C bonds that the XPS also identified.