bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of thermal anneal steps on the current collapse of fluorine treated enhancement mode SiN/AlGaN/GaN HEMTs
Authors: Lorenz Anne , Derluyn Joff , Das Jo , Cheng Kai , Degroote Stefan , Medjdoub Farid , Germain Marianne , Borghs Gustaaf
Published: March 2009

Gallium nitride based high electron mobility transistors offer high carrier density combined with high electron mobility and enable operation at high frequencies, voltages and temperatures. However, they are generally working in depletion mode, requiring a negative bias to switch them off. As this is disadvantageous for circuit design, power consumption and safety of operation, enhancement mode devices would be favourable. This operation mode can be reached by shifting the threshold voltage towards more positive values by implantation of negatively charged fluorine ions. As these ions were reported to form deep level trap states in the material, we investigated the influence of the implantation and subsequent anneal steps on current collapse and threshold voltage. We found that anneal steps of over 550 °C are effective in reducing the current collapse up to factor 4, but also shift the threshold voltage again to negative values, thus eliminating enhancement mode operation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Volmer‐Weber growth mode of InN quantum dots on GaN by MOVPE
Authors: Meissner Christian , Ploch Simon , Pristovsek Markus , Kneissl Michael
Published: March 2009

The growth of indium nitride quantum dots on c‐plane GaN/sapphire was investigated by metal‐organic vapour phase epitaxy using in situ spectroscopic ellipsometry and ex situ atomic force microscopy. Using an ammonia stabilisation for temperatures above 500 °C desorption of InN structures could be prevented during cool down. At a growth temperature of 520 °C and a trimethylindium partial pressure of 0.5 Pa (V/III ratio of 5000) we observe growth without a wetting layer in the Volmer‐Weber mode, indicated by the presence of InN quantum dots for sub‐monolayer coverages and a constant ratio of quantum dot volume to total InN amount. At this transport limited growth regime the typical quantum dot density of 7 × 1010 cm–2 is independent from coverage. Coalescence occurs after 20 s growth time at an average structure diameter of 51 nm as expected for such a density. Smallest uncapped hexagonal structures are realised with an average diameter of 28 nm and a height of 3.1 nm (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energetics of oxygen adsorption and incorporation at InN polar surface: A first‐principles study
Authors: Belabbes A. , Kioseoglou J. , Komninou Ph. , Karakostas Th.
Published: March 2009

First principles calculations are performed to study the adsorption and incorporation of oxygen at InN polar surfaces as a function of oxygen coverage. We find that the adsorption of oxygen at InN surfaces is higher on the N‐polar than on In‐polar. The calculations show that for the low coverage regime (x ≤ 0.5 ML) both orientations are active towards the adsorption of oxygen; this implies that the reaction between the O atoms and the surface is strongly exothermic. As the coverage of O exceeds 0.5 ML a large difference in adsorption energies, of almost 2.5 eV, is observed between (0001) and (000$ \bar 1 $) surfaces indicating that the (000$ \bar 1 $) surface is more active towards oxygen adsorption than the (0001) surface. The high coverage of oxygen changes the surface structure of InN due to the difference in binding energy (O‐In bonds are stronger than In‐N ones). This result shows explicitly that the formation of In adlayer is disturbed by the O adsorption. Concerning the energetics of O incorporation our results show that it is more favourable for O to substitute a N atom in one of the top layers near the surface than in bulk, indicating that there is a strong tendency for O to reside at the surface rather than in subsurface layers. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of a low threading dislocation density ELO‐AlN template for application to deep‐UV LEDs
Authors: Hirayama Hideki , Fujikawa Sachie , Norimatsu Jun , Takano Takayoshi , Tsubaki Kenji , Kamata Norihiko
Published: March 2009

We have fabricated low threading dislocation density (TDD) AlN templates on sapphire substrates for application to deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) by employing an epitaxial lateral overgrowth (ELO) process. An AlN stripe structure with a width of 5 μm and a spacing of 3 μm was formed by using inductive coupled plasma (ICP) etching. The AlN stripes were completely coalesced and embedded to create a flat surface after the growth of an approximately 15 μm‐thick ELO‐AlN layer, grown by low‐pressure metal‐organic chemical vapor deposition (LP‐MOCVD). We systematically investigated the appropriate V/III ratio and growth temperature for the ELO‐AlN. The edge‐type TDD of the AlN was reduced from 2×109 cm–2 (AlN stripe region) to 3×108 cm–2 (in the wing region of the ELO‐AlN), as estimated by cross‐sectional transmission electron microscope (TEM) imaging. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Milliwatt power 270 nm‐band AlGaN deep‐UV LEDs fabricated on ELO‐AlN templates
Authors: Hirayama Hideki , Norimatsu Jun , Noguchi Norimichi , Fujikawa Sachie , Takano Takayoshi , Tsubaki Kenji , Kamata Norihiko
Published: March 2009

We demonstrated CW milliwatt power operations of 270 nm‐band AlGaN multi‐quantum well (MQW) deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) fabricated on epitaxial lateral overgrowth (ELO) AlN templates on sapphire. An initial AlN stripe layer was grown directly on sapphire by using ammonia (NH3) pulse‐flow multilayer (ML) growth method. An AlN stripe structure with a width of 5 μm and a spacing of 3 μm was completely coalesced after the growth of an approximately 15 μm‐thick ELO‐AlN layer grown by low‐pressure metal‐organic chemical vapor deposition (LP‐MOCVD). The edge‐type threading dislocation density (TDD) of the wing region of the ELO‐AlN layer was 3×108 cm‐2, as observed by cross‐sectional transmission electron microscope (TEM) image. The maximum output power of 2.7 mW was obtained from an AlGaN MQW LED with emission wavelength at 273 nm fabricated on ELO‐AlN template under room temperature (RT) CW operation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inhomogeneity of a highly efficient InGaN based blue LED studied by three‐dimensional atom probe tomography
Authors: Gu G. H. , Park C. G. , Nam K. B.
Published: March 2009

The InGaN based multiple quantum well (MQW) structure in a commercially available white light emitting diode (LED) was studied by transmission electron microscopy (TEM) and three‐dimensional atom probe tomography (APT). The average In mole fraction by three‐dimensional (3D) APT was found to be about 18% in the InGaN well which is consistent with the secondary ion mass spectrometry (SIMS) analysis. The In distribution in the InGaN well layer was analyzed by the iso curve mapping of 3D APT and found to be non‐uniform in the InGaN active layer. In clustering or In rich regions in the range of 2–3 nm size were found, in contrast to recent reports. Our results thus indicate that In clustering is essential for high‐brightness InGaN based LEDs. We have also observed a discontinuity in the range of 50–100. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Predicting the Androgenicity of Structurally Diverse Compounds from Molecular Structure Using Different Classifiers
Authors: Ji Li , Wang Xiaodong , Qin Liang , Luo Si , Wang Liansheng
Published: March 2009

Many environmental and industrial chemicals are reported to have androgenic or antiandrogenic activities. These androgenic chemicals may act as hormones and have the potential to disrupt the endocrine systems of wildlife and humans. In this study, the probabilistic neural network (PNN), support vector machine (SVM), and learning vector quantization (LVQ), three types of machine learning, were used to develop binary classification models to predict androgenicity directly from the organic compounds' molecular structures which were represented by only eleven numerical descriptors. The PNN model acquired the best overall classification rate of 86.67% for prediction data set, with Matthews Correlation Coefficient of 0.64, and the LVQ model gave the lowest false negative rate of 0.00%, which will tend to give relatively high priority during toxicology evaluation. In addition, a consensus model was produced that integrated all three of the basic model types. Compared with the individual models, this consensus model correctly predicted the androgenicity of 86.67% of the prediction set compounds, with false negative rate of 0.00% and the highest Matthews Correlation Coefficient of 0.65. The obtained results indicate that the proposed classification models could provide a feasible and practical tool for the rapid screening of potential androgens.
Effective collision strengths for electron‐impact excitation of transitions within the ground 1s2 2s2 2p4 manifold of O‐like Fe18+
Authors: Santana Juan A. , Ishikawa Yasuyuki
Published: March 2009

Collision strengths have been computed for the electron impact excitations of parity and spin forbidden transitions within the ground 1s22s22p4 manifold of Fe XIX (Fe18+). The calculations were carried out using a relativistic R‐matrix close‐coupling method based on the effective many‐body Hamiltonian. Twenty‐six target states were included in the close‐coupling expansion. Effective collision strengths, assuming a Maxwellian electron velocity distribution, were evaluated for all transitions within the ground configuration. Good agreement is found with previous Breit‐Pauli R‐matrix calculations at low electron temperatures, 5.0 ≤ log Te ≤ 6.0 K, for all the transitions, whereas significant differences are found for electron temperatures in the range 6.0 ≤ log Te ≤ 7.0 K. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
First‐principles study of the structure and the electronic structure of yttrium aluminum garnet Y3Al5O12
Authors: Muñoz‐García Ana Belén , Anglada Eduardo , Seijo Luis
Published: March 2009

Density functional theory calculations have been performed on the electronic structure and the atomistic structure of yttrium aluminum garnet Y3Al5O12, YAG, and related crystals (yttrium aluminum perovskite YAlO3, yttria Y2O3, and corundum α‐Al2O3). The quality of the computed data provides reliability to further structural studies with the same methods on local and extended bulk and surface defects in YAG. The structure of the computed conduction band is coherent with available electron‐loss near‐edge spectroscopy (ELNES) data. Previous Y‐Al covalent interactions are not observed here. Reaction energies involving YAG and its related materials are given. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Role of electronic curve crossing of benzene S1 state in the photodissociation of aryl halides, effect of fluorination: RASSI‐SO MS‐CASPT2 study
Authors: Devarajan Ajitha , Gaenko Alexander , Lindh Roland , Malmqvist Per‐Åke
Published: March 2009

An ab initio study of the role of electronic curve crossing of benzene S1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low‐lying n−σ*, π−σ*, π−π* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene π−π* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low‐lying n−σ*, π−σ*, π−π* states were studied including spin‐orbit and relativistic effects using the Restricted Active Space state interaction multistate complete active space perturbation theory (RASSI‐MS‐CASPT2) method. Crossing behavior of spin‐free and spin‐orbit potential energy curves was analyzed for the role of the benzene S1 state. Our results indicate the curve crossing region to be around 2.00–2.35 Å for both C6H5I and C6F5I. Analysis of effect of fluorination on the energies of states corresponding to benzene π−π* and n−σ* transitions suggests an increase in the energy of benzene π−π* states and a decrease in the energy of the states corresponding to n−σ* transitions. Increased spin‐orbit gap, increased separation of the benzene S1(π−π*) state and n−σ* states in the region of curve crossing, lesser mixing of the π−π* and n−σ* states, an order of magnitude decrease in the transition strength to the benzene singlet transition all contributed to the observed substantial increase in the quantum yield of the direct channel product on fluorination of aryl halides. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
A theorem for complex symmetric matrices revisited
Authors: Brändas Erkki J.
Published: March 2009

In this contribution we will revisit the celebrated theorem that every square matrix is similar to a (complex) symmetric matrix and that every symmetric matrix is orthogonally similar to a given normal canonical form. Specifically we will re‐examine the proof as well as the derivation of an explicit n‐dimensional complex symmetric form. We will extend the formula to incorporate the various powers of the original normal form, a derivation not previously provided. Some examples of these complex symmetric forms in chemical and physical applications are indicated. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Matrix‐assisted laser desorption/ionization by using femtosecond laser pulses in the near‐infrared wavelength regime
Authors: Wichmann J. M. , Lupulescu C. , Wöste L. , Lindinger A.
Published: March 2009

We observe a substantial matrix‐assisted laser desorption/ionization (MALDI) signal when irradiating femtosecond laser pulses in the near‐infrared spectral range centered around 800 nm and using standard MALDI matrices with absorption bands in the ultraviolet (UV) regime. The laser pulse energy dependence of this novel phenomenon is investigated in comparison with MALDI with near‐UV laser pulses. Our observations show that multiphoton absorption/ionization could be a major issue among the MALDI processes when the sample is irradiated with ultra‐short laser pulses. Copyright © 2009 John Wiley & Sons, Ltd.
Mass spectrometry of nanodiamonds
Authors: Houška Jan , Panyala Nagender Reddy , Peña‐Méndez Eladia Maria , Havel Josef
Published: March 2009

Detonation nanodiamonds (NDs) were studied by time‐of‐flight mass spectrometry (TOF MS). The formation of singly charged carbon clusters, C, with groups of clusters at n = 1–35, n ∼160–400 and clusters with n ∼8000 was observed. On applying either high laser energy or ultrasound, the position and intensity of the maxima change and a new group of clusters at n ∼70–80 is formed. High carbon clusters consist of an even number of carbons while the percentage of odd‐numbered clusters is quite low (≤5–10%). On increasing the laser energy, the maximum of ionization (at n ∼200 carbons) is shifted towards the lower m/z values. It is suggested that this is mainly due to the disaggregation of the original NDs. However, the partial destruction of NDs is also possible. The carbon clusters (n ∼2–35) are partially hydrogenated and the average value of the hydrogenation was 10–30%. Trace impurities in NDs like Li, B, Fe, and others were detected at high laser energy. Several matrices for ionizing NDs were examined and NDs themselves can also be used as a matrix for the ionization of various organic compounds. When NDs were used as a matrix for gold nanoparticles, the formation of various gold carbides AumCn was detected and their stoichiometry was determined. It was demonstrated that TOF MS can be used advantageously to analyze NDs, characterize their size distribution, aggregation, presence of trace impurities and surface chemistry. Copyright © 2009 John Wiley & Sons, Ltd.
A mass spectrometry based imaging method developed for the intracellular detection of HIV protease inhibitors
Authors: Dekker Lennard J. M. , van Kampen Jeroen J. A. , Reedijk Mariska L. , Burgers Peter C. , Gruters Rob A. , Osterhaus Albert D. M. E. , Luider Theo M.
Published: March 2009

Mass spectrometry imaging is a promising technique for measuring drugs and drug metabolites in cells and tissues. In this manuscript we describe a method for the imaging of HIV protease inhibitors. As a model system we used Mono Mac 6 cells cultured with the HIV protease inhibitors saquinavir and nelfinavir deposited on glass slides using a cytocentrifuge. A sublimation/deposition device for homogeneous matrix deposition was constructed which allows imaging of these HIV protease inhibitors at clinically relevant concentrations. Using this matrix sublimation/deposition method, glass slides containing the cytocentrifuged cells can be measured and analyzed by two types of mass spectrometry techniques, viz. matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) and MALDI Fourier transform ion cyclotron resonance (FTICR), and this makes it possible to perform imaging rapidly (MALDI‐TOF) and with a very high selectivity (MALDI‐FTICR). Copyright © 2009 John Wiley & Sons, Ltd.
Systematic characterization of the covalent interactions between (−)‐epigallocatechin gallate and peptides under physiological conditions by mass spectrometry
Authors: Cao Dong , Zhang Yangjun , Zhang Huihui , Zhong Liangwei , Qian Xiaohong
Published: March 2009

(−)‐Epigallocatechin gallate (EGCG) is a major bioactive component in leaves of green tea, and has been widely investigated for its anti‐tumor activity. The interaction between EGCG and the key peptides or proteins (e.g. glutathione, enzymes) in vivo is thought to be involved in the toxicity and anti‐cancer mechanism of EGCG. However, the true anti‐tumor mechanism of EGCG is not clear, and few studies have focused on the reactivity of EGCG toward peptides or proteins under physiological conditions (pH 7.4, 37°C). In this work, the covalent interactions between EGCG and model peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and α‐NH2 of the N‐terminus of peptides) under physiological condition were fully characterized using mass spectrometry. It was found that EGCG can react with the thiol groups of peptides to form adducts under physiological conditions (pH 7.4, 37°C), even in the absence of the peroxidase/hydrogen peroxide system. Besides the thiol groups of peptides, it is firstly reported that EGCG also reacts with α‐NH2 of the N‐terminus or arginine residues of model peptides to form Schiff base adducts, and the methionine residues of model peptides can be easily oxidized by hydrogen peroxide (H2O2) generated during the process of EGCG auto‐oxidation to form methionine sulfoxide products. The preference for the reaction of nucleophlic residues of peptides with EGCG was determined to have the following order: Cys > α‐NH2 of the N‐terminus > Arg. The neutral loss ions of [M+H–170]+ and [M+H‐138]+ were detected in all tandem mass spectra of the EGCG adducts of peptides, which indicates that these two neutral loss ions can be considered as the characteristic neutral loss ions of peptides modified by EGCG. Results of the present research provide insights into the toxicology and anti‐tumor mechanism of EGCG in vivo. Copyright © 2009 John Wiley & Sons, Ltd.
Identification of hydroxyl radical oxidation products of N‐hexanoyl‐homoserine lactone by reversed‐phase high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry
Authors: Cui Yiling , Frey Rebecca L. , Ferry John L. , Ferguson P. Lee
Published: March 2009

A reversed‐phase high‐performance liquid chromatography/electrospray tandem mass spectrometry method was developed for the characterization of hydroxyl radical oxidation products of N‐hexanoyl‐homoserine lactone (C6‐HSL), a member of the N‐acylhomoserine lactone (AHL) class of microbial quorum‐sensing signaling molecules identified in many Gram‐negative strains of bacteria. Six products were identified: four with molecular weight (MW) of 213 and two with MW of 260. The characteristic product ions formed through collision‐induced dissociation (CID) provided diagnostic structural information. One of the photolysis products was determined to be N‐(3‐oxohexanoyl)homoserine lactone (3OC6‐HSL), a highly active quorum‐sensing signal, by comparison with a reference standard. Three structural isomers with the same mass as 3OC6‐HSL were identified as acyl side chain oxidized C6‐HSL (keto/enol functionalized) by accurate mass measurement and the structures of these products were proposed from CID spectral interpretation. Two structural isomers formed from concurrent oxidation and nitration of C6‐HSL were also observed and their structures were postulated based on CID spectra. In addition to the six hydroxyl radical oxidation products formed from the C6‐HSL precursor, five additional compounds generated from combined oxidation and lactonolysis of C6‐HSL were identified and structures were postulated. Copyright © 2009 John Wiley & Sons, Ltd.
A metabolomic analysis of the toxicity of Aconitum sp. alkaloids in rats using gas chromatography/mass spectrometry
Authors: Sun Bo , Wu Shengming , Li Ling , Li Haijing , Zhang Qi , Chen Hebing , Li Famei , Dong Fangting , Yan Xianzhong
Published: March 2009

A metabolomic investigation of intoxication with Aconitum sp. alkaloids was carried out. Plasma obtained from Wistar rats administered these alkaloids was analyzed using gas chromatography/time‐of‐flight mass spectrometry. Samples were analyzed following protein precipitation, liquid‐liquid extraction, and derivatization. Thirty‐six metabolites were identified among the detected compounds. Subsequent data analysis using the t test and principal component analysis revealed metabolic differences between the control rats and treated groups as well as between the groups of rats administered different alkaloids. Twenty‐seven metabolites were significantly different between plasma samples from the controls and treated groups. The significant decreased plasma levels of glutamine and creatinine in all treated groups suggested impaired heart and muscle function caused by alkaloids. The plasma levels of 22 metabolites in the hypaconitine group were significantly decreased. In contrast, only 8 and 13 metabolites were observed with significantly decreased levels in the aconitine and mesaconitine groups, respectively.These results indicated that Aconitum sp. alkaloids can cause metabolic disorders in rats. The toxicity and corresponding mechanism of hypaconitine was different from those of aconitine and mesaconitine, based on the differences of perturbed metabolic patterns between groups. Copyright © 2009 John Wiley & Sons, Ltd.
The use of limited dependent variable techniques in strategy research: issues and methods
Authors: Wiersema Margarethe F. , Bowen Harry P.
Published: March 2009

Strategy researchers are increasingly turning their attention from examining the impact of strategic choices on firm performance to examining the factors that determine strategic choices at the firm level. This shift of research orientation has meant that researchers are increasingly faced with a limited dependent variable (LDV) that takes a limited number of usually discrete values, for which LDV methods such as logit or probit are required. Despite their growing popularity, there appears to be widespread problems in the use of LDV methods. This research note complements recent studies that offer general guidelines by presenting and illustrating the practical steps needed to implement the methods essential for analyzing and interpreting the results from LDV models. Copyright © 2009 John Wiley & Sons, Ltd.
Value appropriation as an organizational capability: the case of IP protection through patents
Authors: Reitzig Markus , Puranam Phanish
Published: March 2009

We develop and test a theoretical framework that describes the organizational antecedents of value appropriation capabilities in the context of obtaining patent protection. We argue that intermediate levels of cross‐functional involvement across intellectual property (IP) generation, protection, and utilization activities outperform very high or very low levels of functional specialization in terms of obtaining rapid patent protection; while these activities are distinct enough to generate gains from specialization, there are also significant gains to be generated by coordinating across them, which cross‐functional involvement achieves. Using a unique dataset that combines survey and patent (application) data, and multiple estimation techniques, we test and find support for our arguments. Copyright © 2009 John Wiley & Sons, Ltd.
Thermal Deposition of Intact Tetrairon(III) Single‐Molecule Magnets in High‐Vacuum Conditions
Authors: Margheriti Ludovica , Mannini Matteo , Sorace Lorenzo , Gorini Lapo , Gatteschi Dante , Caneschi Andrea , Chiappe Daniele , Moroni Riccardo , de Mongeot Francesco Buatier , Cornia Andrea , Piras Federica M. , Magnani Agnese , Sessoli Roberta
Published: March 2009

A tetrairon(III) single‐molecule magnet is deposited using a thermal evaporation technique in high vacuum. The chemical integrity is demonstrated by time‐of‐flight secondary ion mass spectrometry on a film deposited on Al foil, while superconducting quantum interference device magnetometry and alternating current susceptometry of a film deposited on a kapton substrate show magnetic properties identical to the pristine powder. High‐frequency electron paramagnetic resonance spectra confirm the characteristic behavior for a system with S = 5 and a large Ising‐type magnetic anisotropy. All these results indicate that the molecules are not damaged during the deposition procedure keeping intact the single‐molecule magnet behavior.
Alternative Translation of OCT4 by an Internal Ribosome Entry Site and its Novel Function in Stress Response
Authors: Wang Xia , Zhao Yannan , Xiao Zhifeng , Chen Bing , Wei Zhanliang , Wang Bin , Zhang Jing , Han Jin , Gao Yuan , Li Lingsong , Zhao Hongxi , Zhao Wenxue , Lin Hang , Dai Jianwu
Published: March 2009

OCT4 is a pivotal transcription factor in maintaining the pluripotency and self-renewal capacities of embryonic stem (ES) cells. Human OCT4 can generate two isoforms by alternative splicing, termed OCT4A and OCT4B. OCT4A confers the stemness properties of ES cells, whereas the function of OCT4B is unknown. We present here the diverse protein products and a novel function of OCT4 gene. A single OCT4B mRNA can encode three isoforms by alternative translation initiation at AUG and CUG start codons, respectively. A putative internal ribosome entry site (IRES) has been identified in OCT4B mRNA accounting for the translation mechanism. The OCT4B-190 is upregulated under stress conditions and it may protect cell against apoptosis under stress. This work evokes the significance to distinguish the biological function of the protein products of OCT4. The OCT4 gene, by the regulation of alternative splicing and alternative translation initiation, may carry out more crucial roles in many biological events.

Disclosure of potential conflicts of interest is found at the end of this article.
The importance of surgical education in the accuracy of implant placement during hip fracture fixation
Authors: Parmar Vinay , Kumar A. J. Shyam
Published: March 2009

Background

Studies have found that tip apex distance (TAD) is the strongest independent predictor of lag screw cut-out following hip fracture fixation. The objective of this study was to understand the importance of introducing the concept of TAD to surgeons. The null hypothesis was that there were no differences between fractures fixed before awareness of TAD compared with fractures fixed after awareness of TAD.

Materials and Methods

This study involved assessing 75 consecutive radiographs retrospectively (before introduction of “tip apex distance” to surgeons) and 83 consecutive radiographs prospectively (after introduction of “tip apex distance” to surgeons). Radiographs were measured using a radiograph digitizer and software.

Results

Average TAD in radiographs measured retrospectively was 22.6 mm compared with 9.7 mm in radiographs analysed prospectively (P ≤ 0.001). The power of this study was 97%.

Conclusion

This study demonstrates that introducing the concept of “TAD” to surgeons, will improve the accuracy of lag screw placement during fixation of an extracapsular fracture. The improvements in lag screw placement will undoubted reduce cut-out of the implant post-surgery.
Immediate continuous passive motion after internal fixation of an ankle fracture
Authors: Farsetti Pasquale , Caterini Roberto , Potenza Vito , De Luna Vincenzo , De Maio Fernando , Ippolito Ernesto
Published: March 2009

Background

Surgical treatment is usually mandatory in displaced bimalleolar and trimalleolar fractures. Some authors have recommended early mobilization of the ankle joint after surgical treatment of these lesions. In this study, we evaluate the effect of immediate postoperative continuous passive motion in the management of displaced bimalleolar and trimalleolar fractures treated surgically.

Materials and methods

Two series of 22 patients each, who had had a Weber type A, B or C ankle fracture treated surgically, were followed up at least 10 years after the injury. In the first series, immediately after surgery, a continuous passive motion machine was applied to the operated ankle for 3 weeks, whereas in the second series, after surgery a plaster splint or a plaster cast was applied for 3 weeks.

Results

At follow-up, all patients were evaluated clinically and radiographically using the AOFAS Ankle Hindfoot Score System (Kitaoka, Foot Ankle 15:349–353, 1994). The average final score for the first series of patients was 95.7 points (range 87–100 points, standard deviation 3.42 points). Of this series, at radiographic examination, in two patients we observed minor signs of osteoarthritis of the ankle joint. The average final score for the second series was 88 points (range 68–100 points, standard deviation 10.60 points). At radiographic examination, in six patients we observed minor signs of osteoarthritis of the ankle joint, whereas in another one the osteoarthritis was severe.

Conclusions

Continuous passive motion started immediately after surgery seems to be an effective method both for allowing complete and quick recovery of the range of motion of the ankle and for reducing the risk of early degenerative joint disease. Immediate passive ankle motion can be applied only after adequate reduction and stable internal fixation.
Electron-Spin Precession in Dependence of the Orientation of the External Magnetic Field
Authors: Miah M Idrish
Published: March 2009

Electron-spin dynamics in semiconductor-based heterostructures has been investigated in oblique magnetic fields. Spins are generated optically by a circularly polarized light, and the dynamics of spins in dependence of the orientation (θ) of the magnetic field are studied. The electron-spin precession frequency, polarization amplitude, and decay rate as a function ofθ are obtained and the reasons for their dependences are discussed. From the measured data, the values of the longitudinal and transverse components of the electrong-factor are estimated and are found to be in good agreement with those obtained in earlier investigations. The possible mechanisms responsible for the observed effects are also discussed.
Finite blocking property versus pure periodicity
Authors: MONTEIL THIERRY
Published: March 2009

A translation surface 𝒮 is said to have the finite blocking property if for every pair (O,A) of points in 𝒮 there exists a finite number of ‘blocking’ points B1,…,Bn such that every geodesic from O to A meets one of the Bis. 𝒮 is said to be purely periodic if the directional flow is periodic in each direction whose directional flow contains a periodic trajectory (this implies that 𝒮 admits a cylinder decomposition in such directions). We will prove that the finite blocking property implies pure periodicity. We will also classify the surfaces that have the finite blocking property in genus two: such surfaces are exactly the torus branched coverings. Moreover, we prove that in every stratum such surfaces form a set of null measure. In Appendix A, we prove that completely periodic translation surfaces form a set of null measure in every stratum.
A family of 2-graphs arising from two-dimensional subshifts
Authors: PASK DAVID , RAEBURN IAIN , WEAVER NATASHA A.
Published: March 2009

Higher-rank graphs (ork-graphs) were introduced by Kumjian and Pask to provide combinatorial models for the higher-rank Cuntz–KriegerC*-algebras of Robertson and Steger. Here we consider a family of finite 2-graphs whose path spaces are dynamical systems of algebraic origin, as studied by Schmidt and others. We analyse theC*-algebras of these 2-graphs, find criteria under which they are simple and purely infinite, and compute theirK-theory. We find examples whoseC*-algebras satisfy the hypotheses of the classification theorem of Kirchberg and Phillips, but are not isomorphic to theC*-algebras of ordinary directed graphs.
Unitary representations of wavelet groups and encoding of iterated function systems in solenoids
Authors: DUTKAY DORIN ERVIN , JORGENSEN PALLE E. T. , PICIOROAGA GABRIEL
Published: March 2009

For points indreal dimensions, we introduce a geometry for general digit sets. We introduce a positional number system where the basis for our representation is a fixedd by dmatrix over ℤ. Our starting point is a given pair (A,𝒟) with the matrixAassumed expansive, and 𝒟 a chosen complete digit set, i.e., in bijective correspondence with the points in ℤd/ATℤd. We give an explicit geometric representation and encoding with infinite words in letters from 𝒟. We show that the attractorX(AT,𝒟) for an affine Iterated Function System (IFS) based on (A,𝒟) is a set of fractions for our digital representation of points in ℝd. Moreover our positional ‘number representation’ is spelled out in the form of an explicit IFS-encoding of a compact solenoid 𝒮Aassociated with the pair (A,𝒟). The intricate part (Theorem 6.15) is played by the cycles in ℤdfor the initial (A,𝒟)-IFS. Using these cycles we are able to write down formulas for the two maps which do the encoding as well as the decoding in our positional 𝒟-representation. We show how some wavelet representations can be realized on the solenoid, and on symbolic spaces.
Third harmonic order imaging as a focal spot diagnostic for high intensity laser-solid interactions
Authors: Dromey B. , Bellei C. , Carroll D.C. , Clarke R.J. , Green J.S. , Kar S. , Kneip S. , Markey K. , Nagel S.R. , Willingale L. , McKenna P. , Neely D. , Najmudin Z. , Krushelnick K. , Norreys P.A. , Zepf M.
Published: March 2009

As the state of the art for high power laser systems increases from terawatt to petawatt level and beyond, a crucial parameter for routinely monitoring high intensity performance is laser spot size on a solid target during an intense interaction in the tight focus regime (<10 µm). Here we present a novel, simple technique for characterizing the spatial profile of such a laser focal spot by imaging the interaction region in third harmonic order (3ωlaser). Nearly linear intensity dependence of 3ωlaser generation for interactions >1019 Wcm−2 is demonstrated experimentally and shown to provide the basis for an effective focus diagnostic. Importantly, this technique is also shown to allow in-situ diagnosis of focal spot quality achieved after reflection from a double plasma mirror setup for very intense high contrast interactions (>1020 Wcm−2) an important application for the field of high laser contrast interaction science.
Evaluation of EGNOS Tropospheric Delay Model in South-Eastern Europe
Authors: Kos Tomislav , Botincan Maja , Markezic Ivan
Published: March 2009

The troposphere affects electromagnetic signal propagation causing signal path bending and the alteration of the electromagnetic wave velocity. Tropospheric delay can introduce a considerable error in satellite positioning if it is not properly estimated. The GPS signal delay can vary from 2 to 20 m depending on the elevation angles between the receiver and the satellite. Two basic types of delay prediction models exist. The first use surface meteorological parameters to estimate the value of the tropospheric delay, and the other models that do not require real-time meteorological input use average and seasonal variation data related to the receiver's latitude and day-of-year. This paper compares the performance of both types of model over a period of one year, comprising all seasons, to verify their accuracy over a longer period. The Saastamoinen model, known as one of the best performing prediction models, was taken as a reference and the global EGNOS model was used to check how the global estimates of the yearly averages of the meteorological parameters and their related seasonal variations comply with the real-time surface parameters.
On the Availability of Fault Detection and Exclusion in GNSS Receiver Autonomous Integrity Monitoring
Authors: Wang Jinling , Ober Pieter B.
Published: March 2009

Global Navigation Satellite System (GNSS) Receiver Autonomous Integrity Monitoring (RAIM) is essential for safety-of-life and liability critical applications. This paper discusses two fundamentally different ways to assess the integrity risk of an operation with RAIM, based on a different amount of information available: the expected (or average) performance that is computed using the GNSS models only and the real-time (or actual) performance, which also uses information on the internal status of a GNSS receiver. It is shown both theoretically and by simulation that the real-time integrity risk significantly exceeds the expected risk after the detection and exclusion of a failing satellite. Therefore, while most published RAIM algorithms base their performance assessment on the expected performance only, this is only correct when the requirements allow the risk evaluation to be averaged over multiple operations. However, when the GNSS integrity requirement is to be applied on a ‘per operation’ basis, real-time integrity measures are more appropriate.
Navigation Integration Using the Fuzzy Strong Tracking Unscented Kalman Filter
Authors: Jwo Dah-Jing , Lai Shih-Yao
Published: March 2009

A navigation integration processing scheme, called the strong tracking unscented Kalman filter (STUKF), is based on the combination of an unscented Kalman filter (UKF) and a strong tracking filter (STF). The UKF employs a set of sigma points by deterministic sampling, such that the linearization process is not necessary, and therefore the error caused by linearization as in the traditional extended Kalman filter (EKF) can be avoided. As a type of adaptive filter, the STF is essentially a nonlinear smoother algorithm that employs suboptimal multiple fading factors, in which the softening factors are involved. In order to resolve the shortcoming in traditional approach for selecting the softening factor through personal experience or computer simulation, a novel scheme called the fuzzy strong tracking unscented Kalman filter (FSTUKF) is presented where the Fuzzy Logic Adaptive System (FLAS) is incorporated for determining the softening factor. The proposed FSTUKF algorithm shows promising results in estimation accuracy when applied to the integrated navigation system design, as compared to the EKF, UKF and STUKF approaches.
Error Mechanisms in Indoor Positioning Systems without Support from GNSS
Authors: Michalson William R. , Navalekar Abhijit , Parikh Hemish K.
Published: March 2009

A version of this paper was first presented at the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.

There exist various applications for indoor positioning, amongst which indoor positioning and tracking in urban environments has gained significant attention. Some user communities, like fire fighters, ideally require indoor accuracy of less than one metre, with accuracies of less than six metres acceptable by some other user communities. Achieving this level of accuracy requires a detailed profiling of error sources so that they can be better understood so that, in turn, indoor positioning accuracy in the presence of these errors can be further improved. Some well known error sources like multipath, NLOS (non line of sight), oscillator drift, dilution of precision and others have been studied and can be found in the literature. A less well known error source that can substantially affect indoor positioning accuracy are the effects of the dielectric properties of building materials on propagation delay.

Various RF and non-RF based prototypes that claim to be suitable for indoor positioning can be found in the literature. Most of the existing literature discusses algorithms and summarizes the positioning results that were achieved during field tests using a prototype system or, more commonly, simulations. Little of this existing literature provides a breakdown of the total navigation system errors observed with the objective of analyzing the contribution of each error source independently.

The paper will first provide a brief overview of the precision personnel locator system developed at the Worcester Polytechnic Institute. The field tests and observed indoor positioning results using this RF prototype will then be summarized and used to provide a baseline to establish a system error budget. The total observed error will be broken down and a detailed analysis of each of the error sources will be presented based on actual measured data in a variety of indoor environments. This leads to a better understanding of how each error source affects indoor positioning accuracy. Each of the error sources can then be independently optimized to minimize the observed errors. Specifically, the interplay between the dielectric properties and multipath profiles will be highlighted. This paper will conclude by presenting an error budget which can be used as a practical lower bound when designing precise indoor positioning systems.
GPS Jamming and the Impact on Maritime Navigation
Authors: Grant Alan , Williams Paul , Ward Nick , Basker Sally
Published: March 2009

Versions of this paper were first presented at the Royal Institute of Navigation GNSS Vulnerabilities and Solutions Conference held at Baska, Croatia in September 2008 and the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.

The US Global Positioning System (GPS) is currently the primary source of Position, Navigation and Timing (PNT) information in maritime applications, whether stand-alone or augmented with additional systems. This situation will continue in the future with GPS, possibly together with other Global Navigation Satellite Systems (GNSS) e.g. Galileo, being the core PNT technology for e-Navigation – the future digital maritime architecture. GPS signals, measured at the surface on the Earth, are very weak. As such, the system is vulnerable to unintentional interference and jamming, resulting in possible denial of service over large geographical areas. The result of such interference could be the complete failure of the mariner's GPS receiver or, possibly worse, the presentation to the mariner of hazardously misleading information (HMI) for navigation and situational awareness, depending on how the GPS receiver reacts to the jamming incident. Recognising this, the General Lighthouse Authorities of the United Kingdom and Ireland (GLA), in collaboration with the UK Ministry of Defence (MOD) Defence Science and Technology Laboratory (DSTL), have conducted a series of sea-trials with the aim of identifying the full effects of GPS jamming on safe navigation at sea.

This paper presents the key findings of these trials and provides important information on the effect of GPS denial. The GLA are playing a pivotal role in the establishment of eLoran as an independent source of PNT, taking advantage of eLoran's complementary nature, having dissimilar failure modes to GPS and the future GNSS. This paper provides information on the performance of an eLoran receiver in an area of GPS service denial. The paper presents the rationale for the work, details the system architecture employed, the data gathering efforts and finally the data analysis procedures, results and conclusions.
GPS and Inertial Systems for High Precision Positioning on Motorways
Authors: Naranjo J. E. , Jiménez F. , Aparicio F. , Zato J.
Published: March 2009

The accurate location of a vehicle in the road is one of the most important challenges in the automotive field. The need for accurate positioning affects several in-vehicle systems like navigators, lane departure warning systems, collision warning and other related sectors such as digital cartography suppliers. The aim of this paper is to evaluate high precision positioning systems that are able to supply an on-the-centimetre accuracy source to develop on-the-lane positioning systems and to be used in future applications as an information source for autonomous vehicles that circulate at high speeds on public roads. In this paper we have performed some on-road experiments, testing several GPS-based systems: Autonomous GPS; RTK Differential GPS with a proprietary GPS base station; RTK Differential GPS connected to the public GPS base station network of the National Geographic Institute of Spain via vehicle-to-infrastructure GPRS communications; and GPS combination with inertial measurement systems (INS) for position accuracy maintenance in degraded satellite signal reception areas. In these tests we show the validity and the comparison of these positioning systems, allowing us to navigate, in some cases, on public roads at speeds near 120 km/h and up to 100 km from the start position without any significant accuracy reduction.
Virtual evolution for visual search in natural images results in behavioral receptive fields with inhibitory surrounds
Authors: ZHANG SHENG , ABBEY CRAIG K. , ECKSTEIN MIGUEL P.
Published: March 2009

The neural mechanisms driving perception and saccades during search use information about the target but are also based on an inhibitory surround not present in the target luminance profile (e.g., Eckstein et al., 2007). Here, we ask whether these inhibitory surrounds might reflect a strategy that the brain has adapted to optimize the search for targets in natural scenes. To test this hypothesis, we sought to estimate the best linear template (behavioral receptive field), built from linear combinations of Gabor channels representing V1 simple cells in search for an additive Gaussian target embedded in natural images. Statistically nonstationary and non-Gaussian properties of natural scenes preclude calculation of the best linear template from analytic expressions and require an iterative optimization method such as a virtual evolution via a genetic algorithm. Evolved linear receptive fields built from linear combinations of Gabor functions include substantial inhibitory surround, larger than those found in humans performing target search in white noise. The inhibitory surrounds were robust to changes in the contrast of the signal, generalized to a larger calibrated natural image data set, and tasks in which the signal occluded other objects in the image. We show that channel nonlinearities can have strong effects on the observed linear behavioral receptive field but preserve the inhibitory surrounds. Together, the results suggest that the apparent suboptimality of inhibitory surrounds in human behavioral receptive fields when searching for a target in white noise might reflect a strategy to optimize detection of signals in natural scenes. Finally, we contend that optimized linear detection of spatially compact signals in natural images might be a new possible hypothesis, distinct from decorrelation of visual input and sparse representations (e.g., Graham et al., 2006), to explain the evolution of center–surround organization of receptive fields in early vision.