bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved ruggedness of an ion‐pairing liquid chromatography/tandem mass spectrometry assay for the quantitative analysis of the triphosphate metabolite of a nucleoside reverse transcriptase inhibitor in peripheral blood mononuclear cells
Authors: Zhao Yue , Liu Guowen , Liu Yifei , Yuan Long , Hawthorne Dara , Shen Jim X. , Guha Mausumee , Aubry Anne
Published: December 2012

RATIONALE

Nucleotide analogs are highly polar and ionic, which impose great challenges on bioanalysis. Ion‐pairing liquid chromatography/tandem mass spectrometry (LC/MS/MS) is the predominant reported approach for such compounds. Assay ruggedness of ion‐pairing LC/MS/MS methods was often a challenge due to the potential contamination of the ion source of the mass spectrometer and LC column performance deterioration caused by ion‐pairing reagents.

METHODS

An ion‐pairing reagent was only added to the reconstitution solution to minimize its exposure to the MS ion source. To achieve optimum sensitivity, high pH mobile phases and negative ion ESI were needed for the LC/MS/MS method. However, high pH mobile phases led to the accumulation of ion‐pairing reagent on the analytical column, which was washed off with an acidic solution to restore the column performance. In addition, isopropanol was used as a mobile phase modifier to improve peak shape and sensitivity.

RESULTS

The limit of detection was established at 1.0 ng/mL in the cell lysate. The calibration curve showed good linearity over the range of 1.0 to 100 ng/mL. The overall accuracy was no less than 87.7% based on four levels of quality control samples. Inter‐run precision and intra‐run precision across four analytical runs for low, geometric, medium and high QCs were less than 12.9.

CONCLUSIONS

By identifying and addressing the root cause of the assay ruggedness problem, we have developed a rugged ion‐pairing LC/MS/MS method for a triphosphate (TP) metabolite of BMS‐986001 in peripheral blood mononuclear cells. The new method overcame challenges such as a rapid deterioration of the peak shape, increased carryover and extremely poor column life. The peak shape was well maintained throughout multiple analytical runs. This method has been successfully applied to a toxicology study in cynomolgus monkey. Copyright © 2012 John Wiley & Sons, Ltd.
Influence of various endogenous and artefact modifications on large‐scale proteomics analysis
Authors: Bienvenut Willy V. , Sumpton David , Lilla Sergio , Martinez Aude , Meinnel Thierry , Giglione Carmela
Published: December 2012

RATIONALE

Some large‐scale proteomics studies in which strong cation exchange chromatography has been applied are used to determine proteomes and post‐translational modification dynamics. Although such datasets favour the characterisation of thousands of modified peptides, e.g., phosphorylated and N‐α‐acetylated, a large fraction of the acquired spectra remain unexplained by standard proteomics approaches. Thus, advanced data processing allows characterisation of a significant part of these unassigned spectra.

METHODS

Our recent investigation of the N‐α‐acetylation status of plant proteins gave a dataset of choice to investigate further the in‐depth characterisation of peptide modifications using Mascot tools associated with relevant validation processes. Such an approach allows to target frequently occurring modifications such as methionine oxidation, phosphorylation or N‐α‐acetylation, but also the less usual peptide cationisation. Finally, this dataset offers the unique opportunity to determine the overall influence of some of these modifications on the identification score.

RESULTS

Although methionine oxidation has no influence and tends to favour the characterisation of protein N‐terminal peptides, peptide alkalinisation shows an adverse effect on peptide average score. Nevertheless, peptide cationisation appears to favour the characterisation of protein C‐terminal peptides with a limited to no direct influence on the identification score. Unexpectedly, our investigation reveals the unfortunate combination of the molecular weight of N‐α‐acetylation and potassium cation that mimics the mass increment of a phosphorylation group.

CONCLUSIONS

Since these characterisations rely upon computational treatment associated with statistical validation approaches such as 'False discovery rates' calculation or post‐translational modification position validation, our investigation highlights the limitation of such treatment which is biased by the initial searched hypotheses. Copyright © 2012 John Wiley & Sons, Ltd.
Fragmentation characteristics and isomeric differentiation of flavonol O‐rhamnosides using negative ion electrospray ionization tandem mass spectrometry
Authors: Ablajan Keyume , Tuoheti Anagu
Published: December 2012

RATIONALE

Flavonoids exhibit a wide range of biological activities. The differentiation and structural characterization of the flavonol O‐rhamnosides and their isomers are important research topics. Electrospray ionization tandem mass spectrometry (ESI‐MSn) is an indispensable tool and has become an efficient method for the identification of bioactive natural products.

METHODS

Negative ion ESI‐MSn was used to characterize and differentiate flavonol O‐rhamnosides and their isomeric compounds. The collision energies in collision‐induced dissociation were varied to optimize the structural information.

RESULTS

Flavonol 7‐O‐rhamnosides containing either a hydroxyl or a methoxyl group at the C‐8 position clearly differed from their isomeric compounds, such as the flavonol 3‐O‐rhamnosides, in the product ion spectra of the [M–H]– ions. The differences in the locations of the glycosyl group and OCH3 group resulted in a significant change in the relative abundances of the Y0– and [Y0–H]–• ions, and the formation of some characteristic ions, such as 1,3A0– and [1,3A0–CH3]–•.

CONCLUSIONS

An efficient ESI‐MSn method for the structural identification and isomeric differentiation of flavonol O‐rhamnosides was developed. The differences in the glycosyl type, and the glycosylation and methoxylation positions in the structures of isomeric flavonoids, can be determined using (–)ESI‐MSn spectra. The formation and relative abundances of [Y0–H]–• and Y0– ions, as well as the comparison of some diagnostic ions, are vital in the differentiation of isomeric flavonoids. These results have practical applications in the rapid identification of flavonol O‐rhamnosides present in crude bioactive extracts. Copyright © 2012 John Wiley & Sons, Ltd.
Surface excitations in electron spectroscopy. Part I: dielectric formalism and Monte Carlo algorithm
Authors: Salvat‐Pujol F. , Werner W. S. M.
Published: December 2012

The theory describing energy losses of charged non‐relativistic projectiles crossing a planar interface is derived on the basis of the Maxwell equations, outlining the physical assumptions of the model in great detail. The employed approach is very general in that various common models for surface excitations (such as the specular reflection model) can be obtained by an appropriate choice of parameter values. The dynamics of charged projectiles near surfaces is examined by calculations of the induced surface charge and the depth‐ and direction‐dependent differential inelastic inverse mean free path (DIIMFP) and stopping power. The effect of several simplifications frequently encountered in the literature is investigated: differences of up to 100% are found in heights, widths, and positions of peaks in the DIIMFP. The presented model is implemented in a Monte Carlo algorithm for the simulation of the electron transport relevant for surface electron spectroscopy. Simulated reflection electron energy loss spectra are in good agreement with experiment on an absolute scale. Copyright © 2012 John Wiley & Sons, Ltd.
Golgi phosphoprotein 4 (GPP130) is a sensitive and selective cellular target of manganese exposure
Authors: Masuda Melisa , Braun‐Sommargren Michelle , Crooks Dan , Smith Donald R.
Published: December 2012

Chronic elevated exposure to manganese (Mn) is associated with neurocognitive and fine motor deficits in children. However, relatively little is understood about cellular responses to Mn spanning the transition between physiologic to toxic levels of exposure. Here, we investigated the specificity, sensitivity, and time course of the Golgi Phosphoprotein 4 (GPP130) response to Mn exposure in AF5 GABAergic neuronal cells, and we determined the extent to which GPP130 degradation occurs in brain cells in vivo in rats subchronically exposed to Mn. Our results show that GPP130 degradation in AF5 cells was specific to Mn, and did not occur following exposure to cobalt, copper, iron, nickel, or zinc. GPP130 degradation occurred without measurable increases in intracellular Mn levels and at Mn exposures as low as 0.54 µM. GPP130 protein was detectable by immunofluorescence in only ∼15–30% of cells in striatal and cortical rat brain slices, and Mn‐exposed animals exhibited a significant reduction in both the number of GPP130‐positive cells, and the overall levels of GPP130 protein, demonstrating the in vivo relevance of this Mn‐specific response within the primary target organ of Mn toxicity. These results provide insight into specific mechanism(s) of cellular Mn regulation and toxicity within the brain, including the selective susceptibility of cells to Mn cytotoxicity. Synapse 67:205–215, 2013. © 2012 Wiley Periodicals, Inc.
Changes in the circadian rhythm of mRNA expression for µ‐opioid receptors in the periaqueductal gray under a neuropathic pain‐like state
Authors: Takada Tomohiko , Yamashita Akira , Date Akitoshi , Yanase Makoto , Suhara Yuki , Hamada Asami , Sakai Hiroyasu , Ikegami Daigo , Iseki Masako , Inada Eiichi , Narita Minoru
Published: December 2012

Variation in the production of opioid receptors over a 24‐h period is considered to contribute to circadian alterations in neuropathic pain. In this study, we investigated the possible changes in the circadian rhythm of mRNA expression for µ‐opioid receptor (MOR), κ‐opioid receptor (KOR), and adrenaline α2a receptor (α2a) in the periaqueductal gray, frontal cortex, thalamus, and spinal cord following sciatic nerve ligation in mice. In sham‐operated mice, the latencies of hind paw‐withdrawal in response to thermal stimuli at 14:00 and 20:00 were significantly greater than that at 8:00 and the latency at 2:00 was significantly less than those at 14:00 and 20:00, indicating a “rest” period‐dominant circadian rhythm for thermal pain‐thresholds. In sciatic nerve‐ligated mice, the latencies of hind paw‐withdrawal in response to thermal stimuli at 14:00 and 20:00 were significantly less than that at 8:00, and the latency at 2:00 was significantly greater than those at 14:00 and 20:00. A correlative tendency between the time‐variation of pain latency and the time‐variation of MOR mRNA expression was observed in the periaqueductal gray of sham‐operated and sciatic nerve‐ligated mice. In contrast, neither mouse showed a strong circadian rhythm for the expressions of KOR and α2a mRNAs in any region. The present data suggest that changes in MOR mRNA expression in the periaqueductal gray may be synchronized with the circadian rhythm for the pain threshold for noxious thermal stimuli. In contrast, neuropathic pain in mice exhibited a negative circadian pattern for the expression of MOR, KOR, and α2a receptors in the frontal cortex, thalamus, and spinal cord. Synapse 67:216–223, 2013. © 2012 Wiley Periodicals, Inc.
Re: Hematologic profile of neonates with growth restriction is associated with rate and degree of prenatal Doppler deterioration. A. A. Baschat, M. Kush, C. Berg, U. Gembruch, K. H. Nicolaides, C. R. Harman, O. M. Turan. Ultrasound Obstet Gynecol 2013; 41: 66–72
Authors: Bhide A.
Published: December 2012

Linked Comment: Ultrasound Obstet Gynecol 2013:41:66–72
Bridging across cognitive training and brain plasticity: a neurally inspired computational model of interactive skill learning
Authors: Fu Wai‐Tat , Lee Hyunkyu , Boot Walter R. , Kramer Arthur F.
Published: December 2012

This article reviews recent empirical and brain imaging data on effects of cognitive training methods on complex interactive skill learning, and presents a neurally inspired computational model that characterizes the effects of these training methods. In particular, the article focuses on research that shows that variable priority training (VPT), which requires learners to shift their priorities to different task components during training, often leads to better acquisition and retention of skills than fixed priority training (FPT). However, there is only weak evidence that shows that VPT can enhance transfer of complex interactive skills to untrained situations. Brain imaging studies show that VPT leads to significantly lower activations and a higher reduction of activities in attentional control areas after training than FPT. Research also shows that the volume of the striatum predicts the learning effects, but only in VPT. The computational model, developed based on learning mechanisms at the neural level, bridges across the empirical and the braining imaging results by explaining the effects of VPT and FPT at both the behavioral and neural levels. The results were discussed in the context of previous findings on cognitive training.WIREs Cogn Sci2013, 4:225–236. doi: 10.1002/wcs.1214

This article is categorized under:

Psychology > Learning
P2Y receptors in neurogenesis
Authors: Illes Peter , Messemer Nanette , Rubini Patrizia
Published: December 2012

G protein‐coupled P2Y receptors (Rs) regulate the function of embryonic and adult neural precursor cells (NPCs) which have the capacity to regenerate and give rise to cells belonging to all three major linages of the nervous system: neurons, oligodendrocytes and astrocytes. The presence of mRNA and protein for various P2YRs have been demonstrated by RT‐PCR, immunohistochemistry and western‐blotting in NPCs. In agreement with the sensitivity of different subtypes of P2YRs to purine and pyrimidine nucleotides, the ATP‐responsive P2Y1R and the ATP/UTP‐responsive P2Y2R both released intracellular Ca2+ from its storage sites in NPCs. Nucleotide‐induced Ca2+ oscillations have a signaling function in NPC syncitia and appear to be involved in cellular proliferation. Two further NPC functions regulated by P2Y receptors are migration and differentiation, especially through P2Y1R‐activation, although P2Y2Rs may also participate. WIREs Membr Transp Signal 2013, 2:43–48. doi: 10.1002/wmts.76

For further resources related to this article, please visit the WIREs website.
Provenance of Pleistocene Rhine River Middle Terrace sands between the Swiss–German border and Cologne based on U–Pb detrital zircon ages
Authors: Krippner Anne , Bahlburg Heinrich
Published: December 2012

Detrital zircon U–Pb age distributions derived from samples representing ancient or relatively young large-scale continental drainage networks are commonly taken to reflect the geochronological evolution of the tapped continental area. Here, we present detrital zircon U–Pb ages and associated heavy mineral data from Pleistocene Rhine River Middle Terrace sands and equivalents between the Swiss–German border and Cologne in order to test the commonly assumed Alpine provenance of the material. Samples from eight localities were analyzed for their heavy mineral assemblages. Detrital zircon U–Pb ages were determined by laser ablation inductively coupled mass spectrometry on selected samples from five locations along the Rhine River. The zircon age populations of all samples show a similar distribution, their main peaks being between 300 and 500 Ma. Minor age populations are recognized at 570 and 1,070 Ma. The 300–400 Ma maximum reflects the Variscan basement drained by or recycled into the Rhine River and its tributaries. The 400–500 Ma peak with predominantly Early Silurian ages points to Baltica or to the mid-German crystalline rise as original sources. One distinct peak at c. 570 Ma probably represents input from Cadomian terranes. The Precambrian U–Pb ages are compatible with derivation from sources in Baltica and in northern Gondwana. The heavy mineral populations of Middle Terrace sands and equivalents are characterized to a variable extend by garnet, epidote, and green hornblende. This association is often referred to as the Alpine spectrum and is considered to be indicative of an Alpine provenance. However, hornblende, epidote, and garnet are dominant heavy minerals of collisional orogens in general and may also be derived from Variscan and Caledonian units or from intermittent storage units. A remarkable feature of the detrital zircon age distribution in the Rhine River sediments from the Swiss–German border to Cologne is the absence of ages younger than 200 Ma and in particular of any ages reflecting the Alpine orogeny between c. 100 and 35 Ma. Sediments from rivers draining the equally collisional Himalaya orogen contain detrital zircons as young as 20 Ma. Our results question the assumption that Pleistocene Rhine River sediments were directly derived from the Alps. The lag time between the formation and deposition age of the youngest zircon in the studied Pleistocene Rhine River deposits is 200 Ma. Together with the absence of Alpine zircon ages, this stresses that detrital zircon age data from ancient sedimentary units found in poorly understood tectonic or paleogeographic settings need to be interpreted with great care, one could miss an entire orogenic cycle.
Short rigid scope and stereo‐scope designed specifically for open abdominal navigation surgery: clinical application for hepatobiliary and pancreatic surgery
Authors: Onda Shinji , Okamoto Tomoyoshi , Kanehira Masaru , Fujioka Shuichi , Suzuki Naoki , Hattori Asaki , Yanaga Katsuhiko
Published: December 2012

Background

We have reported the utility of an image display system using augmented reality (AR) technology in hepatobiliary surgery under laparotomy. Among several procedures, we herein report a system using a novel short rigid scope and stereo‐scope, both designed specifically for open abdominal navigation surgery, and their clinical application for hepatobiliary and pancreatic surgery.

Methods

The 3D reconstructed images were obtained from preoperative computed tomography data. In our specialized operating room, after paired‐point matching registration, the reconstructed images are overlaid onto the operative field images captured by the short rigid scopes. The scopes, which are compact and sterilizable, can be used in the operative field. The stereo‐scope provides depth information. Eight patients underwent operations using this system, including hepatectomy in two, distal pancreatectomy in three, and pancreaticoduodenectomy in three patients. The stereo‐scope was used in five patients.

Results

All eight operations were performed safely using the novel short rigid scopes, and stereo images were acquired in all five patients for whom the stereo‐scope was used. The scopes were user friendly, and the intraoperative time requirement for our system was reduced compared with the conventional method.

Conclusions

The novel short rigid scope and stereo‐scope seem to be suitable for clinical use in open abdominal navigation surgery. In hepatobiliary and pancreatic surgery, our novel system may improve the safety, accuracy and efficiency of operations.
Phase II study of sunitinib in Japanese patients with unresectable or metastatic, well-differentiated pancreatic neuroendocrine tumor
Authors: Ito Tetsuhide , Okusaka Takuji , Nishida Toshirou , Yamao Kenji , Igarashi Hisato , Morizane Chigusa , Kondo Shunsuke , Mizuno Nobumasa , Hara Kazuo , Sawaki Akira , Hashigaki Satoshi , Kimura Nobuyuki , Murakami Mami , Ohki Emiko , Chao Richard C. , Imamura Masayuki
Published: December 2012

Background. Pancreatic neuroendocrine tumors (NETs) are rare but are frequently diagnosed at advanced stages and require systemic therapy. Patients and methods. This multicenter, open-label, phase II study evaluated sunitinib in Japanese patients with well-differentiated pancreatic NET. Patients received sunitinib 37.5 mg/day on a continuous daily dosing (CDD) schedule. The primary endpoint was clinical benefit rate (CBR; percentage of complete responses [CRs] plus partial responses [PRs] plus stable disease [SD] ≥24 weeks). Secondary endpoints included objective response rate (ORR), tumor shrinkage, progression-free survival (PFS) probability, safety, pharmacokinetics, and biomarkers. Results. Twelve patients received treatment. The CBR was 75 % (95 % confidence interval [CI], 43–94) and included 6 patients with a PR and 3 with SD. The ORR was 50 % (95 % CI, 21–79). PFS probability was 91 % (95 % CI, 54–99) at 6 months and 71 % (95 % CI, 34–90) at 12 months. Commonly reported treatment-emergent (all-causality), any-grade adverse events included diarrhea (n = 10), hand–foot syndrome and hypertension (both n = 8), fatigue and headache (both n = 7), and neutropenia (n = 6). No deaths on study were reported; one death due to disease progression occurred >28 days after end of treatment. Sunitinib on a CDD schedule resulted in sustained drug concentrations without accumulation across cycles. Tumor responses in all 12 patients did not appear to correlate with decreases in chromogranin A levels. Conclusions. Sunitinib 37.5 mg/day on a CDD schedule demonstrated antitumor activity in Japanese patients with unresectable, well-differentiated pancreatic NET. Commonly reported adverse events were consistent with the known safety profile of sunitinib.
Molecular Ion‐Independent Quantification of Polar Glycerolipid Classes in Marine Plankton Using Triple Quadrupole MS
Authors: Popendorf Kimberly J. , Fredricks Helen F. , Van Mooy Benjamin A. S.
Published: December 2012

Polar glycerolipids are a diverse family of lipid molecules that form the bulk of bacterial and eukaryotic microbial membranes. The earth and ocean sciences has a long history of using fatty acids as biomarkers for microbes, but have only recently begun to examine the intact polar lipids from which they are derived. Current analytical approaches rely on laboriously quantifying the molecular ions of each of these species independently. Thus, we saw a need for a method for quantifying polar glycerolipid classes that was: (i) selective for individual classes, (ii) inclusive of all species within a class, (iii) independent of foreknowledge of the molecular ions of the polar glycerolipid, and (iv) amenable to automated, high‐throughput data analysis methods. Our new HPLC‐electrospray‐ionization triple‐quadrupole MS (HPLC‐ESI‐TQMS) method can be applied to quantify the nine major classes of polar glycerolipid in planktonic communities: the phospholipids phosphatidylglycerol, phosphatidylethanolamine, and phosphatidylcholine; the glycolipids monoglycosyldiacylglycerol, diglycosyldiacylglycerol and sulfoquinovosyldiacylglycerol; and the betaine lipids diacylglyceryl trimethyl homoserine, diacylglyceryl hydroxymethyl trimethyl‐β‐alanine, and diacylglyceryl carboxyhydroxymethylcholine. The analyses rely on neutral loss and parent ion scan events that yield one chromatogram for each class of polar glycerolipid, simplifying downstream analysis and increasing sample throughput. The efficacy of the method was demonstrated by analyzing plankton community samples from a variety of marine environments.
Simulations to Assess Phase II Noninferiority Trials of Different Doses of Capecitabine in Combination With Docetaxel for Metastatic Breast Cancer
Authors: Bruno R , Lindbom L , Schaedeli Stark F , Chanu P , Gilberg F , Frey N , Claret L
Published: December 2012

A phase II trial in metastatic breast cancer (MBC) (NO16853) failed to show noninferiority (progression‐free survival, PFS) of capecitabine 825 mg/m2 plus docetaxel 75 mg/m2 to the registered capecitabine dose of 1,250 mg/m2 plus docetaxel 75 mg/m2. We developed a modeling framework based on NO16853 and the pivotal phase III MBC study, SO14999, to characterize the link between capecitabine dose, tumor growth, PFS, and survival to simulate response to a range of capecitabine doses and determine a minimum capecitabine dose noninferior to 1,250 mg/m2. Simulation showed NO16853 had little power to demonstrate noninferiority (69%). The power reached 80% with a 1,000 mg/m2 starting dose and an increased number of PFS events. A starting dose of 1,000 mg/m2 could be established as noninferior in terms of efficacy to the registered dose in the second‐line MBC setting, with a potentially improved safety, in line with medical practice.

CPT: Pharmacometrics & Systems Pharmacology (2012) 1, e19; doi:10.1038/psp.2012.20; advance online publication 26 December 2012
NVU dynamics. III. Simulating molecules at constant potential energy
Authors: Ingebrigtsen Trond S. , Dyre Jeppe C.
Published: December 2012

This is the final paper in a series that introduces geodesic molecular dynamics at constant potential energy. This dynamics is entitled NVU dynamics in analogy to standard energy-conserving Newtonian NVE dynamics. In the first two papers [T. S. Ingebrigtsen, S. Toxvaerd, O. J. Heilmann, T. B. Schrøder, and J. C. Dyre, J. Chem. Phys. 135, 104101 (2011)10.1063/1.3623585; T. S. Ingebrigtsen, S. Toxvaerd, T. B. Schrøder, and J. C. Dyre, J. Chem. Phys. 135, 104102 (2011)10.1063/1.3623586], a numerical algorithm for simulating geodesic motion of atomic systems was developed and tested against standard algorithms. The conclusion was that the NVU algorithm has the same desirable properties as the Verlet algorithm for Newtonian NVE dynamics, i.e., it is time-reversible and symplectic. Additionally, it was concluded that NVU dynamics becomes equivalent to NVE dynamics in the thermodynamic limit. In this paper, the NVU algorithm for atomic systems is extended to be able to simulate the geodesic motion of molecules at constant potential energy. We derive an algorithm for simulating rigid bonds and test this algorithm on three different systems: an asymmetric dumbbell model, Lewis-Wahnström o-terphenyl (OTP) and rigid SPC/E water. The rigid bonds introduce additional constraints beyond that of constant potential energy for atomic systems. The rigid-bond NVU algorithm conserves potential energy, bond lengths, and step length for indefinitely long runs. The quantities probed in simulations give results identical to those of Nosé-Hoover NVT dynamics. Since Nosé-Hoover NVT dynamics is known to give results equivalent to those of NVE dynamics, the latter results show that NVU dynamics becomes equivalent to NVE dynamics in the thermodynamic limit also for molecular systems.
A new experimental setup for making thermal emission measurements in a simulated lunar environment
Authors: Thomas I. R. , Greenhagen B. T. , Bowles N. E. , Donaldson Hanna K. L. , Temple J. , Calcutt S. B.
Published: December 2012

One of the key problems in determining lunar surface composition for thermal-infrared measurements is the lack of comparable laboratory-measured spectra. As the surface is typically composed of fine-grained particulates, the lunar environment induces a thermal gradient within the near sub-surface, altering the emission spectra: this environment must therefore be simulated in the laboratory, considerably increasing the complexity of the measurement. Previous measurements have created this thermal gradient by either heating the cup in which the sample sits or by illuminating the sample using a solar-like source. This is the first setup able to measure in both configurations, allowing direct comparisons to be made between the two. Also, measurements across a wider spectral range and at a much higher spectral resolution can be acquired using this new setup. These are required to support new measurements made by the Diviner Lunar Radiometer, the first multi-spectral thermal-infrared instrument to orbit the Moon. Results from the two different heating methods are presented, with measurements of a fine-grained quartz sample compared to previous similar measurements, plus measurements of a common lunar highland material, anorthite. The results show that quartz gives the same results for both methods of heating, as predicted by previous studies, though the anorthite spectra are different. The new calibration pipeline required to convert the raw data into emissivity spectra is described also.
Band bending and determination of band offsets in amorphous/crystalline silicon heterostructures from planar conductance measurements
Authors: Varache R. , Kleider J. P. , Favre W. , Korte L.
Published: December 2012

An analytical model for the calculation of the band bending in amorphous/crystalline silicon (a-Si:H/c-Si) heterojunctions is presented and validated by comparison with full numerical simulations. The influence of the various structure properties and parameters, such as the density of states in bulk a-Si:H or at interface defects, the position of the Fermi level in a-Si:H, the temperature dependence of band gaps, is investigated. Significant band offsets imply the presence of a strong inverted layer at the c-Si surface of both (p)a-Si:H/(n)c-Si and (n)a-Si:H/(p)c-Si structures, forming two-dimensional hole and electron gases, respectively. This leads to high sheet carrier densities that have been evidenced from planar conductance measurements. Experimental data obtained on samples coming from various research institutes are analyzed with our model in order to extract the band offsets. We find that the valence band offset ranges between 0.32 and 0.42 eV with an average value at 0.36 eV; the conduction band offset is found between 0.08 and 0.26 eV with a mean value at 0.15 eV. These values are discussed in the frame of the branch point theory for band line-up; they imply that the branch point energy in a-Si:H is almost independent of doping and lies close to mid-gap.
Exchange bias related coercivity enhancement as a characterization tool
Authors: Kosub T. , Bachmatiuk A. , Makarov D. , Baunack S. , Neu V. , Wolter A. , Rümmeli M. H. , Schmidt O. G.
Published: December 2012

We present a phenomenological approach to access the coercivity enhancement which appears in all exchange bias systems. The coercivity enhancement is correlated to the structural properties of the thin film system. We find that the coercivity reacts sensitively to structural changes as subtle as a sub-monolayer interface oxidation of a ferromagnetic layer. We apply our approach to demonstrate the role of surface oxidation in a [Pt/Co]3 layer stack. The intriguing occurrence of antiferromagnetic interlayer coupling in these systems is discussed to be strongly related to the cover layer properties.
Low-rank spectral expansions of two electron excitations for the acceleration of quantum chemistry calculations
Authors: Schwerdtfeger Christine A. , Mazziotti David A.
Published: December 2012

Treatment of two-electron excitations is a fundamental but computationally expensive part of ab initio calculations of many-electron correlation. In this paper we develop a low-rank spectral expansion of two-electron excitations for accelerated electronic-structure calculations. The spectral expansion differs from previous approaches by relying upon both (i) a sum of three expansions to increase the rank reduction of the tensor and (ii) a factorization of the tensor into geminal (rank-two) tensors rather than orbital (rank-one) tensors. We combine three spectral expansions from the three distinct forms of the two-electron reduced density matrix (2-RDM), (i) the two-particle 2D, (ii) the two-hole 2Q, and the (iii) particle-hole 2G matrices, to produce a single spectral expansion with significantly accelerated convergence. While the resulting expansion is applicable to any quantum-chemistry calculation with two-particle excitation amplitudes, it is employed here in the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)]10.1103/PhysRevLett.101.253002. The low-rank parametric 2-RDM method scales quartically with the basis-set size, but like its full-rank version it can capture multi-reference correlation effects that are difficult to treat efficiently by traditional single-reference wavefunction methods. Applications are made to computing potential energy curves of HF and triplet OH+, equilibrium bond distances and frequencies, the HCN-HNC isomerization, and the energies of hydrocarbon chains. Computed 2-RDMs nearly satisfy necessary N-representability conditions. The low-rank spectral expansion has the potential to expand the applicability of the parametric 2-RDM method as well as other ab initio methods to large-scale molecular systems that are often only treatable by mean-field or density functional theories.
Excitation dependent photoluminescence study of Si-rich a-SiNx:H thin films
Authors: Kumar Bommali Ravi , Preet Singh Sarab , Rai Sanjay , Mishra P. , Sekhar B. R. , Vijaya Prakash G. , Srivastava P.
Published: December 2012

We report photoluminescence (PL) investigations on Si-rich amorphous hydrogenated silicon nitride (a-SiNx:H) thin films of different compositions, using three different excitation lasers, viz., 325 nm, 410 nm, and 532 nm. The as-deposited films contain amorphous Si quantum dots (QDs) as evidenced in high resolution transmission electron microscopy images. The PL spectral shape is in general seen to change with the excitation used, thus emphasizing the presence of multiple luminescence centres in these films. It is found that all the spectra so obtained can be deconvoluted assuming Gaussian contributions from defects and quantum confinement effect. Further strength to this assignment is provided by low temperature (300 °C) hydrogen plasma annealing of these samples, wherein a preferential enhancement of the QD luminescence over defect luminescence is observed.
Pre-curving analysis of an opening crack in a magnetoelectroelastic strip under in-plane impact loadings
Authors: Hu Keqiang , Chen Zengtao
Published: December 2012

An opening crack in a magnetoelectroelastic strip under in-plane mechanical, electric, and magnetic impact loadings is considered for magneto-electrically impermeable and permeable crack surface boundary conditions. Laplace and Fourier transforms are applied to reduce the mixed boundary value problem of the crack to dual integral equations, which are expressed in terms of Fredholm integral equations of the second kind. The asymptotic fields near the crack tip are obtained in explicit form and the corresponding field intensity factors are defined. The crack curving phenomena are investigated by applying the criterion of maximum hoop stress intensity factors. Numerical results show that the hoop stress intensity factors are influenced by the electric and magnetic loadings and the geometric size ratios.
Splitting of self-collimated beams in two-dimensional sonic crystals
Authors: Li Bo , Guan Jun-Jun , Deng Ke , Zhao Heping
Published: December 2012

An easy-to-implement scheme to split self-collimated acoustic beams in sonic crystals (SCs) is proposed by introducing line-defects into SCs, by which an incoming self-collimated beam can be split into a 90°-bended one and a transmitted one with an arbitrary power ratio by adjusting the value of defect size. An all-angle and wide-band splitting instrument is demonstrated with nearly perfect efficiency (more than 90%) for Gaussian beams at a wide range of incident angles. Splitting effect for a point source as input is also realized, in which two subwavelength images of the source, i.e., a bended one and a transmitted one, are formed by our designed splitting structure. Finally, the proposed one-to-two splitting scheme is generalized to one-to-N (N > 2) cases by inserting more rows of line defects into the SC.
Controlled joining of Ag nanoparticles with femtosecond laser radiation
Authors: Huang H. , Liu L. , Peng P. , Hu A. , Duley W. W. , Zhou Y.
Published: December 2012

We show that it is possible to tailor the gap separation and interface geometry between adjacent Ag nanoparticles (NPs) by controlling fluence when irradiating with pulses from a fs laser. Unirradiated samples extracted from aqueous solution consist of networks of Ag NPs coated with polyvinylpyrrolidone (PVP). At low laser fluence, bonding between NPs occurs via the formation of an intervening hydrogenated amorphous carbon (α-C:H) layer resulting from the laser-induced decomposition of PVP. This occurs when electrons are emitted at hot-spots created by the trapping of plasmons. The thickness of the α-C:H layer determines the minimum separation between NPs. Ag NPs with different contact geometries can be produced by irradiation of the networks in solution at fluences exceeding the threshold for the formation of α-C:H. At fluences between 200 and 380 μJ/cm2, the α-C:H interface layer is replaced with a metallic neck. Surface enhanced Raman scattering (SERS) has been used to quantify the electromagnetic field enhancement in joined NP samples. We find that Ag NPs bonded by α-C:H and exhibiting a narrow gap possess the highest SERS enhancement.
Electronic structure mechanism of martensitic phase transformation in binary titanium alloys
Authors: Dai J. H. , Wu X. , Song Y. , Yang R.
Published: December 2012

Influence of alloying elements M (M = Al, Cr, Cu, Fe, Mo, Nb, Ni, Sn, Ta, V, W, and Zr) on phase stability and elastic properties of titanium was studied by first principles total energy calculations. The formation energies of various phases of binary Ti-M alloys are evaluated to identify the influence of alloying elements on phase stability and transformation. The results show a similar dependency of the formation energy on the concentration of alloying elements in various phases: the β, α′, α″, and ω phases. All alloying elements stabilize the β phase and show similar influence of the stabilities of the α′ and α″ phases, but only Al and Sn can increase the stability of the ω phase. The elastic parameters of α″-Ti alloys are also studied in the present work. All alloys have smaller Young's modulus than the pure titanium except the Al and Cu contained alloys, which also show larger bulk and shear moduli than the pure Ti. Elements Cr, Mo, Ni, Sn, Zr, Al, and Cu could stabilize the alloys both energetically and mechanically. Sn and Cr cause the elastic anisotropies, while Zr and Al greatly increase the isotropic properties. The electronic structures are evaluated to study the intrinsic mechanisms of how alloying elements influence the phase stability and transformation and elastic properties of titanium.
Anisotropic wrinkle formation on shape memory polymer substrates
Authors: Chen Zhongbi , Young Kim Yun , Krishnaswamy Sridhar
Published: December 2012

In this paper, we demonstrate an assisted self-assembly fabrication method for unidirectional patterns using pre-programmed shape memory polymer (SMP) as the substrate in an organic/inorganic bi-layer structure. By heating the hybrid structure above the SMP's shape recovery temperature, the substrate expands because of positive coefficients of thermal expansion in one direction, while in the perpendicular direction it shrinks due to shape memory effect overpowering thermal expansion. Consequently, the metal thin film coated on the substrate is subjected to an orthogonal compression-tension stress field and forms unidirectional wavy patterns. The experimentally obtained wrinkles are well-aligned with uniform wavelength ranging from about 930 nm to 5 μm corresponding to various programming strains and film thicknesses. A parametric study was carried out to study the influence of programming strain and film thickness on wrinkle wavelength and amplitude. The results were compared with a finite deformation model and showed good agreement with theoretical predictions. A simple analytical model incorporating a progressive damage scheme and visco-elasticity is proposed to explain defect formation and post-buckling pattern evolution, respectively. The present study is expected to offer a convenient and simple path of fabricating large-scale unidirectional wavy patterns. A potential application to organic photovoltaics is discussed.
Surface contributions to the alternating current and direct current magnetic properties of oleic acid coated CoFe2O4 nanoparticles
Authors: McDannald A. , Staruch M. , Jain M.
Published: December 2012

In the present work, we have studied the surface layer effects on the dc and ac magnetic measurements of oleic-acid coated CoFe2O4 nanoparticles. The blocking temperature for the nanoparticles is found to be 278 K with 100 Oe field and above this temperature, the nanoparticles show superparamagnetic behavior. A spin-glass correction term to the Bloch law (to account for a magnetically disordered surface layer) was found to accurately describe the temperature dependence of the saturation magnetization. By studying the frequency dependence of the ac magnetization, the coated nanoparticles were shown to have moderate particle interaction strength with anisotropy energy and anisotropy constant of 160 meV and 2.23 × 105 erg/cm3, respectively. A feature in the ac magnetization at 53 K was confirmed to be the result of surface spin-glass freezing on the individual particles. Because of decreased interaction strength due to the oleic acid coating, the presence of a magnetically disordered surface layer due to superexchange frustration (possibly as a result of decreased oxygen ion coordination) was observed.
Strain effects on magnetic characteristics of ultrathin La0.7Sr0.3MnO3 in epitaxial La0.7Sr0.3MnO3/BaTiO3 superlattices
Authors: Shen Xuan , Mo Dan , Li Chen , Wu Di , Li Aidong
Published: December 2012

A series of La0.7Sr0.3MnO3 (LSMO)/BaTiO3 (BTO) superlattices with fixed period thickness have been deposited on SrTiO3 (001) single-crystal substrates using pulsed laser deposition. X-ray diffraction and atomic force microscopy measurements reveal well-defined superstructures with smooth surface morphology. Magnetization and (magneto-)resistance of these [(LSMO)m/(BTO)n]5 superlattices are characterized as a function of the relative thickness m/n in each period. Saturated magnetization is observed to decrease as m/n decreases. The splitting in zero-field cooling/field cooling magnetization curves and the enhanced magnetoresistance imply the coexistence and the competition of ferromagnetic and antiferromagnetic interactions in the ultrathin LSMO layers due to a magnetic inhomogeneity along the direction perpendicular to the sample surface. The inhomogeneity and the ferromagnetic/antiferromagnetic competition can be tuned by residual strain in the superlattices through designing the relative thickness of LSMO and BTO.
Defect engineering of the oxygen-vacancy clusters formation in electron irradiated silicon by isovalent doping: An infrared perspective
Authors: Londos C. A. , Sgourou E. N. , Chroneos A.
Published: December 2012

Infrared spectroscopy was used to study the production and evolution of oxygen–vacancy (VOn for n = 1, 2, 3 and VmO for m = 1, 2, 3) clusters, in electron-irradiated Czochralski silicon (Cz-Si) samples, doped with isovalent dopants. It was determined that the production of the VO pair is enhanced in Ge-doped Si but is suppressed in Sn and Pb-doped Si. The phenomenon is discussed in terms of the competition between isovalent dopants and oxygen atoms in capturing vacancies in the course of irradiation. In the case of Ge, only transient GeV pairs form, leading finally to an increase of the VO production. Conversely, for Sn and Pb the corresponding pairs with vacancies are stable, having an opposite impact on the formation of VO pairs. Regarding V2O and V3O clusters, our measurements indicate that Ge doping enhances their formation, although Sn and Pb dopants suppress it. Similar arguments as those for the VO pair could be put forward, based on the effect of isovalent impurities on the availability of vacancies. Additionally, it was found that the conversion ratio of VO to VO2 decreases as the covalent radius of the isovalent dopant increases. These results are discussed in terms of the local strains introduced by the isovalent dopants in the Si lattice. These local strains affect the balance of the intrinsic defects created as a result of irradiation, as well as the balance between the two main reactions (VO + Oi → VO2 and VO + SiI → Oi) participating in the VO annealing, leading finally to a decrease of the VO2 production. The larger the covalent radius of the isovalent dopant (rGe < rSn < rPb), the larger the introduced strains in the lattice and then the less the VO2 formation in accordance with our experimental results. Interestingly, an opposite trend was observed for the conversion ratio of VO2 to VO3. The phenomenon is attributed to the enhanced diffusivity of oxygen impurity as a result of the presence of isovalent dopants, leading to an enhanced formation of the VO3 cluster. The results indicate that isovalent doping of Si is an effective way to control the formation of the deleterious oxygen-vacancy clustering that can affect Si-based devices.
Application of non-metal doped titania for inverted polymer solar cells
Authors: Siuzdak Katarzyna , Abbas Mamatimin , Vignau Laurence , Devynck Mélanie , Dubacheva Galina V. , Lisowska-Oleksiak Anna
Published: December 2012

Inverted bulk-heterojunction polymer solar cells have been fabricated applying non-metal doped TiO2 as electron extraction buffer layers. Spin-coated films from nitrogen, sulphur, and iodine doped TiO2 nanoparticles dispersed in dimethyl sulphoxide showed comparable roughness and uniformity as those from the pure TiO2 nanoparticles. The highest power conversion efficiency (PCE) of 1.67% was obtained for N-doped TiO2, whereas in the case of pure TiO2, PCE was around 1%. The highest short circuit current density (Jsc = 10.66 mA cm−2) was achieved for I-doped TiO2. Moreover, it was observed that devices with doped TiO2 exhibit better stability under constant illumination comparing to the control devices with pure TiO2.
Structural and optoelectronic properties of Eu2+-doped nanoscale barium titanates of pseudo-cubic form
Authors: Borah Manjit , Mohanta Dambarudhar
Published: December 2012

The effect of europium (Eu)-doping on the optoelectronic carrier transition properties of pseudo-cubic barium titanate (BT) nanostructured system is being reported. Referring to x-ray diffractograms, apart from the diffraction peaks related to perovskite BT structure, non-existence of any additional peaks due to byproducts has revealed that Eu has undergone substitutional doping into BT host lattice. We speculate that adequate growth of a cubic overlayer over the tetragonal core has led to suppressed tetragonality (c/a ratio) features. We notice substantial decrease in the carrier transition exponent (n value), from its normal value, when doping level was varied within 0%-14%. While the overall photoluminescence response is improved with Eu-doping, the BT system was expected to experience concentration quenching. The emission peak at ∼455 nm was attributed to Eu2+ mediated 4f65d1→4f7 carrier transitions. Investigating optoelectronic properties of non-ferroelectric perovskite nanostructured system has a direct relevance in nanoscale optics and optoelectronic components.
Stimulated crystallization of melt-quenched Ge2Sb2Te5 films employing femtosecond laser double pulses
Authors: Cotton Rebecca L. , Siegel Jan
Published: December 2012

The phase transformation of Ge2Sb2Te5 films from the melt-quenched amorphous phase into the crystalline phase induced by 800 nm, 100 fs laser pulses has been studied. For partly amorphized films, progressive crystallization could be induced by single pulses, which can be explained by growth of already existing crystalline embryos. For completely amorphized films, it was not possible to induce crystallization with one or two consecutive pulses; three pulses being the threshold for the onset of crystallization. By employing a fs laser double pulse with an adjustable inter-pulse delay, partial crystallization could be triggered for a delay range of 200 fs–100 ps, while for longer delays no crystallization was possible. The time window for stimulated crystallization can be related to the relaxation dynamics of free electrons excited by the first pulse, which are further excited by the second pulse still remaining in the excited state. Our results indicate that the lifetime of excited electrons in melt-quenched amorphous Ge2Sb2Te5 is ≈100 ps.