bluuebunny/crossref_metadata_2025 huggingface dataset:
Aluminum Doping by Low-Temperature Homoepitaxial Growth for Ni Ohmic Contacts to p-Type 4H-SiC
Authors: Krishnan Bharat , Kotamraju Siva Prasad , Melnychuk Galyna , Merrett Neil , Koshka Yaroslav
Published: March 2009

Low-temperature halo-carbon homoepitaxial growth is suitable for selective epitaxial growth of 4H-SiC using SiO2 mask. A possibility of achieving high values of doping in combination with the selective growth makes it an alternative to ion implantation for selective doping in SiC. In this work, TMA doping in situ during a blanket low-temperature epitaxial growth was utilized to produce heavily Al doped SiC layers for Ohmic contact formation to p-type SiC. Nearly featureless epilayer morphology with Al atomic concentration exceeding 3x1020 cm-3 was obtained after growth at 13000C with the growth rate of 1.5 µm/hr. Ni TLM contacts with a thin adhesion layer of Ti were formed. The as-deposited metal contacts were almost completely Ohmic even before annealing. The specific contact resistance of 2x10-2 Ohm-cm2 and 6x10-5 Ohms-cm2 was achieved without and with contact annealing respectively. The resistivity of the epitaxial layers better than 0.01 Ohm cm was measured for Al atomic concentration of 2.7x1020 cm-3.
A Comprehensive Study of Hydrogen Etching on the Major SiC Polytypes and Crystal Orientations
Authors: Frewin Christopher L. , Coletti Camilla , Riedl Christian , Starke Ulrich , Saddow Stephen E.
Published: March 2009

A comprehensive study on the hydrogen etching of numerous SiC polytype surfaces and orientations has been performed in a hot wall CVD reactor under both atmospheric and low pressure conditions. The polytypes studied were 4H and 6H-SiC as well as 3C-SiC grown on Si substrates. For the hexagonal polytypes the wafer surface orientation was both on- and off-axis, i.e. C and Si face. The investigation includes the influence of the prior surface polishing method on the required etching process parameters. 3C-SiC was also studied grown in both the (100) and (111) orientations. After etching, the samples were analyzed via atomic force microscopy (AFM) to determine the surface morphology and the height of the steps formed. For all cases the process conditions necessary to realize a well-ordered surface consisting of unit cell and sub-unit cell height steps were determined. The results of these experiments are summarized and samples of the corresponding AFM analysis presented.
Electrochemical Polishing of p-Type 4H SiC
Authors: Ke Yue , Yan Fei , Devaty Robert P. , Choyke Wolfgang J.
Published: March 2009

This article discusses the electrochemical polishing of silicon-face p-type 4H SiC using diluted aqueous HF solution. Etchings on the silicon and carbon faces of SiC samples are performed and compared. The experimental results show that the RMS surface roughness of the electrochemically polished Si-face could be as low as about 2 nm. Carbon-face electrochemical polishing gives a rougher surface. Therefore, silicon-face 4H SiC is a better candidate for MEMS processing. The underlying mechanism is also discussed.
SiC Freestanding Micromechanical Structures on Silicon-On-Insulator Substrates
Authors: Placidi Marcel , Zielinski Marcin , Abadal Gabriel , Montserrat Josep , Godignon Philippe
Published: March 2009

The fabrication of freestanding SiC microstructures on Silicon-On-Insulator (SOI) and semi-insulating Silicon substrates is reported. SiC layers were grown on SOI and semi-insulating Si by chemical vapour deposition (CVD) and to avoid the instability currently obtained in SOI structures, the growth process parameters have been optimized. Isotropic wet chemical etching of the Si sacrificial layer released the electrostatic SiC microstructures patterned by dry etching. Moreover a new concept for reducing the gap between resonators and electrodes by the uses of bistable mobile electrodes is introduced.
4H-SiC Schottky Barrier Diodes Using Mo-, Ti- and Ni-Based Contacts
Authors: Perrone Denis , Naretto Marco , Ferrero Sergio , Scaltrito Luciano , Pirri C. Fabrizio
Published: March 2009

We have studied different Schottky and ohmic contacts on 4H-SiC with the aim to obtain Schottky barrier diodes (SBDs) capable to operate at high temperatures, frequencies and power densities for long periods of time, and showing low power losses. The control of the Schottky barrier plays an important role in minimizing the power loss of a SBD, and the metal-semiconductor interface properties strongly affect the overall performances of such a device. Schottky contacts were deposited using Ni, Ti, Ti/Al, Mo and Mo/Al layers, and the annealing treatments have been performed up to 600 °C using a rapid thermal annealing process (RTA). Ohmic contacts have been deposited on the wafer backside using Ti/Al or Ti/Ni/Ag layers. The Schottky diodes have been characterized by means of standard current-voltage (I-V) and capacitance-voltage (C-V) techniques. Schottky diodes with Mo and Mo/Al barriers show a lower barrier height and better overall performances in forward polarization when compared to the Ti- and Ni-based contacts.
Post Annealing Etch Process for Improved Reverse Characteristics of 4H-SiC Diode
Authors: Kang In Ho , Bahng Wook , Joo Sung Jae , Kim Sang Cheol , Kim Nam Kyun
Published: March 2009

The effects of post annealing etch process on electrical performances of a 4H-SiC Schottky diodes without any edge termination were investigated. The post etch was carried out using various dry the dry etch techniques such as Inductively Coupled Plasma (ICP) and Neutral Beam Etch (NBE) in order to eliminate suspicious surface damages occurring during a high temperature ion activation process. The leakage current of diodes treated by NBE measured at -100V was about one order lower than that of diode without post etch and a half times lower than that of diode treated by ICP without a significant degradation of forward electrical characteristics. Based on the above results, the post annealing process was adapted to a junction barrier Schottky diode with a field limiting ring. The blocking voltages of diode without post annealing etch and diodes treated by ICP and NBE were -1038V, -1125V, and -1595V, respectively.
Avalanche Breakdown Characteristics of 4H-SiC Graded p+-n Junction Formed with Aluminum Ion-Implanted p+-Layer
Authors: Ono Shuichi , Katakami S. , Arai Manabu
Published: March 2009

The avalanche breakdown characteristics of a graded p+-n junction formed with aluminum ion-implantation for 4H-SiC were investigated. The breakdown voltage of the graded p+-n junction was calculated using a commercial process/device simulator and considering the ion-implanted distribution of aluminum. To compare the calculated results to the experimental results, a p+/n/n+ diode with an aluminum ion-implanted p+-layer was fabricated on a 2.8-μm-thick 1.1 × 1017-cm-3 n-type epitaxial layer. The breakdown voltage of the fabricated diode showed a higher breakdown voltage than that of the calculation. The cause of the difference in the breakdown voltages between the fabricated diode and the calculation is discussed.
Doping Level Dependence of Electrical Properties for p+n 4H-SiC Diode Formed by Al Ion Implantation
Authors: Satoh Masataka , Nagata Shohei , Nakamura Tohru , Doi Hiroshi , Shibagaki Masami
Published: March 2009

Electrical properties of p+n 4H-SiC(0001) diode formed by Al ion implantation to n-type epitaxial layer have been investigated as a function of Al doping concentration ranging from 1 x 1020 to 6 x 1020 /cm3 and the operation temperature. The n-type 4H-SiC(0001) epitaxial layer with a net donor concentration of 1 x 1016 /cm3 are multiply implanted by Al ions in the energy range from 30 to 170 keV at elevated temperature of 500 oC with a implantation layer thickness of 350 nm, followed by the annealing at 1900 oC for 1min using EBAS. On-state resistance of diode with Al concentration of 1 x 1020 /cm3 is estimated to be about 4.5 mcm2, while that for diode with Al concentration of 6 x 1020 /cm3 is 1.8 mcm2 at 25 oC. In the sample with Al concentration of 6 x 1020 /cm3 shows the positive temperature coefficient of on-state resistance of diode, while that for sample with Al concentration less than 3 x 1020 /cm3 is negative. The diode formed by Al implantation at the concentration of 6 x 1020 /cm3 is able to operate at the constant current density of 80 A/cm2 at the bias of 2.9 V independent to operation temperature.
Polyimide Passivation Effect on High Voltage 4H-SiC PiN Diode Breakdown Voltage
Authors: Diaham Sombel , Locatelli Marie Laure , Lebey Thierry , Raynaud Christophe , Lazar Mihai , Vang Heu , Planson Dominique
Published: March 2009

A polyimide (PI) has been used for the passivation of maximum 7.8 kV 4H-SiC P+N–N+ (PiN) diodes with a 60 µm-thick base epilayer and a junction termination extension (JTE) periphery protection. The dielectric strength of PI films is studied versus area and temperature. The reverse electrical characterization of the PI–passivated PiN diodes is presented for different natures of the environmental atmosphere. The results are compared to those obtained from same devices passivated with a deposited SiO2 thick film. The highest experimental breakdown voltages are obtained for PI–passivated PiN diodes immersed in PFPE oil, with a 5-6 kV typical value, and a 7.3 kV maximum value. Experimental observations are discussed in correlation with the insulating film properties.
Initial Stage Modification for 6H-SiC Single Crystal Grown by the Physical Vapor Transport (PVT) Method
Authors: Choi Jung Woo , Son Chang Hyun , Choi Jong Mun , Lee Gi Sub , Lee Won Jae , Kim Il Soo , Shin Byoung Chul , Ku Kap Ryeol
Published: March 2009

Two SiC single crystal ingots were prepared using sublimation PVT techniques through the different process procedure and then their crystal quality was systematically compared, because the present research was focused to improve the quality of SiC crystal by modifying the initial stage of the PVT growth. Before the main growth step for growing SiC bulk crystal, initial stage period where growth rate was kept to relatively low rate of <10μm/h was introduced to conventional process procedure. N-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC was successfully fabricated. As compared to the characteristics of SiC crystal grown using the conventional schedule, the quality of SiC crystal grown with modifying the initial stage was significantly improved, exhibiting decrease of defect formation such as micropipe and polytype formation.
Critical Issues for MOS Based Power Devices in 4H-SiC
Authors: Ryu Sei Hyung , Dhar Sarit , Haney Sarah K. , Agarwal Anant K. , Lelis Aivars J. , Geil Bruce , Scozzie Charles
Published: March 2009

In this paper, we present the effects of MOS channel processing on the threshold voltage and the MOS field effect mobility of 4H-SiC MOSFETs. By increasing the p-well doping concentration by two orders of magnitude, the threshold voltage could be shifted positive from 0V to 5 V when a thermal oxide layer with NO post oxidation anneal was used as the gate dielectric layer. However, a severe degradation of MOS field effect mobility, decreasing from 37 cm2/Vs to 5 cm2/Vs, was also observed. Using a different processing technique, which uses a deposited oxide layer with an NO anneal, a threshold voltage of 7.5 V and a MOS field effect mobility of 15 cm2/Vs could be achieved. A 10 kV, 1 A power DMOSFET was demonstrated with this technique. A DMOSFET turn-off voltage of 5.25 V was measured at room temperature, which shifted to 3.0 V at 250oC, providing acceptable noise margins throughout the operating temperature range.
Improved On-Current of 4H-SiC MOSFETs with a Three-Dimensional Gate Structure
Authors: Nanen Yuichiro , Yoshioka Hironori , Noborio Masato , Suda Jun , Kimoto Tsunenobu
Published: March 2009

4H-SiC (0001) MOSFETs with a three-dimensional gate structure, which has a top channel on the (0001) face and side-wall channels on the {11-20} face have been fabricated. The three-dimensional gate structures with a 1-5 m width and 0.8 m height have been formed by reactive ion etching, and the gate oxide has been deposited by plasma-enhanced chemical vapor deposition and then annealed in N2O ambient at 1300°C. The fabricated MOSFETs have exhibited superior characteristics: ION / IOFF, the subthreshold swing and VTH are 1010, 250 mV/decade and 3.5 V, respectively. The drain current normalized by the gate width is increasing with decreasing the gate width. The normalized drain current of a 1 m-wide MOSFET is ten times higher than that of a conventional planar MOSFET.
Implantation-Free Low On-Resistance 4H-SiC BJTs with Common-Emitter Current Gain of 50 and High Blocking Capability
Authors: Ghandi Reza , Lee Hyung Seok , Domeij Martin , Buono Benedetto , Zetterling Carl Mikael , Östling Mikael
Published: March 2009

In this study, high voltage blocking (2.7 kV) implantation-free SiC Bipolar Junction Transistors with low on-state resistance (12 mΩ•cm2) and high common-emitter current gain of 50 have been fabricated. A graded base doping was implemented to provide a low resistive ohmic contact to the epitaxial base. This design features a fully depleted base layer close to the breakdown voltage providing an efficient epitaxial JTE without ion implantation. Eliminating all ion implantation steps in this approach is beneficial for avoiding high temperature dopant activation annealing and for avoiding generation of life-time killing defects that reduces the current gain. Also in this process large area transistors showed common-emitter current gain of 38 and open-base breakdown voltage of 2 kV.
Influence of Defects in 4H-SiC Avalanche Photodiodes on Geiger-Mode Dark Count Probability
Authors: Vert Alexey V. , Soloviev Stanislav I. , Fronheiser Jody , Sandvik Peter M.
Published: March 2009

4H-SiC single photon avalanche diodes are reported. A separate absorption and multiplication non-reach through device structure was optimized for operation in Geiger mode. An estimated dark current at a gain of 1000 was ranging between 0.4 pA (0.75 nA/cm2) and 20nA (38 A/cm2) on devices with an effective mesa diameter of 260 m. The electron beam induced current technique was used to image defects in the active region of studied devices. Increased reverse bias leakage current and increased Geiger mode dark count probability were correlated with the presence of large number of defects. Single photon detection efficiencies of up to 11% were measured at a wavelength of 266 nm in Geiger mode.
Comparison of SiC-JFET and Si-IGBT Inverter Losses
Authors: Koch Immo , Canders Wolf Rüdiger
Published: March 2009

Because of the fixed chip size of available sample devices a comparison of SiC-JFET and silicon IGBT with another fixed chip size necessitates the regard to the active area of the chip. The paper presents measurement results considering the active area and shows a comparison of inverter losses depending on junction temperature and switching frequency.
Electrical Properties of Ni/GaN Schottky Contacts on High-Temperature Annealed GaN Surfaces
Authors: Iucolano Ferdinando , Roccaforte Fabrizio , Giannazzo Filippo , Di Franco Salvatore , Moschetti Giuseppe , Puglisi Valeria , Raineri Vito
Published: March 2009

The recent improvement of GaN material quality launched new perspective for its application in power devices. However, ion-implanted guard-ring edge terminations, necessary to improve the breakdown voltage, are not well developed as in SiC technology. Indeed, the effects of high-temperature annealing, required for the electrical activation of the implanted species in GaN, on the electrical behaviour of Schottky contact was not reported. In this work, the influence of high temperature annealing (1150-1200°C) on the surface morphology of GaN and on the electrical behaviour of Schottky contact was studied. Although the morphology of GaN surface did not substantially change after annealing, a worsening of the electrical behaviour of Schottky contact was observed. This latter was ascribed to the formation of a high density of interface states after annealing.
Improved Current Gain in GaN/SiC Heterojunction Bipolar Transistors by Insertion of Ultra-Thin AlN Layer at Emitter-Junction
Authors: Miyake Hiroki , Kimoto Tsunenobu , Suda Jun
Published: March 2009

GaN/SiC Heterojunction Bipolar Transistors (HBTs) with ultra-thin AlN insertion layers at the n-GaN/p-SiC emitter junction are proposed to improve carrier injection efficiency. The current-voltage characteristics of n-GaN/AlN/p-SiC heterojunctions have exhibited very small reverse leakage and good rectification. The capacitance-voltage measurement have revealed that the conduction band offset between n-GaN and p-SiC has been reduced from -0.74 eV to -0.54 eV by insertion of AlN, indicating that the GaN/AlN/SiC heterojunction may show better electron-injection efficiency. A significantly improved common-base current gain (α~0.2) is obtained for GaN/AlN/SiC HBTs with initial N* pre-irradiation, while it was very low (α~0.001) for GaN/SiC HBTs without AlN layers.
Pollen loads and pollen diversity on bodies of Eulonchus tristis (Diptera: Acroceridae): implications for pollination and flower visitation
Authors: Borkent Christopher J. , Schlinger Evert I.
Published: March 2009

Acroceridae is a family of spider-parasitic flies that often visit flowers as adults, although little is known about their possible role as pollinators. Eulonchus tristis Loew visiting flowers of Brodiaea elegans Hoover (Liliaceae s.l.) and Iris douglasiana Herbert (Iridaceae) were collected in California. Individuals carried large pollen loads, although visitors to B. elegans carried significantly more pollen grains than visitors to I. douglasiana. Visitors to B. elegans also carried a higher percentage of focal-plant pollen (91%) than visitors to I. douglasiana (38%). There was no difference in the diversity of pollen species (approximately nine) carried by visitors to either plant species. For visitors to B. elegans, no difference was seen in the amount or diversity of pollen carried with respect to the sex of the visitor. The behaviour potentially resulting in the acquisition of these pollen loads is discussed. These results show that E. tristis has the potential to be an important pollinator for these plant species, particularly B. elegans.
Host selection byAgrilus planipennis(Coleoptera: Buprestidae): inferences from sticky-band trapping
Authors: Lyons D. Barry , de Groot Peter , Jones Gene C. , Scharbach Roger
Published: March 2009

Sticky-band trapping experiments were undertaken in 2003–2006 to examine the host-seeking behaviour of the emerald ash borer,Agrilus planipennisFairmaire, in woodlots in southwestern Ontario, Canada. The female proportion ofA. plannipennisemerging from host logs ranged from 0.414 to 0.582. Landings on sticky-band traps varied more with the female proportion, ranging from 0.392 to 0.889, with the majority in the upper range, suggesting behavioural differences between the sexes. Correlations between landing density and tree size measured as diameter at breast height were positive or showed no relationship. In some locations more beetles were captured on the south side of the tree than on the north side; however, there was no difference between these cardinal directions at other locations. Numbers of captured beetles were never significantly greater on the north side of boles. We observed greater landing densities of adults of both sexes on traps on trees along the edges of woodlots than on trees within the woodlots. When given a choice under natural conditions, beetles landed almost exclusively on host trees (Fraxinus pennsylvanicaMarsh. (Oleaceae)) rather than on other common trees species (Carya ovata(Mill.) K. Koch (Juglandaceae),Tilia americanaL. (Tiliaceae), and species ofAcerL. (Aceraceae)) found in the same woodlots. Our data suggest thatA. planipennismake host-selection decisions while in flight rather than landing randomly. Implications for monitoringA. plannipennisusing sticky-band traps and understanding its host-seeking behaviour are discussed.
Eucalyptus
Authors: Labate Carlos Alberto , de Assis Teotônio Francisco , Oda Shinitiro , de Mello Eduardo José , González Esteban Roberto , Zauza Edival A. Valverde , Mori Edson Seizo , de Moraes Mario Luiz Teixeira , Cid Luis Pedro Barrueto , Alfenas Acelino Couto , Foelkel Celso , Moon David H. , de Carvalho Mayra Costa da Cruz Gallo , Caldas Danielle Gregorio Gomes , Carneiro Raphael Tozelli , de Andrade Alexander , Salvatierra Guilhermo Rafael
Published: March 2009

The genusEucalyptusis currently an important source of timber, cellulose pulp, and energy in a world that is becoming increasingly more conscious of the need to use renewable resources. This chapter initially explains the importance of hybridization and cloning techniques in intensive breeding programs that occurred in Brazil during the last few decades. The strength of these programs is based on the selection of the genetic material and the evaluation of the factors that can influence the expected genetic gains in forestry breeding programs using seeds. Factors such as endogamy, floral development, pollen viability, and pollination are discussed together with seed vigor and the influence of environmental factors on correct evaluation of candidate material. The recent application of molecular markers in eucalypt breeding programs is also mentioned with particular emphasis on genetic diversity, genotyping, and their association with disease resistance. An introduction into Eucalyptus tissue culture is also given as a prelude to the current status of genetic transformation using biolistics andAgrobacterium tumefaciensin this genus. The final sections describe the current challenges, disease resistance, and wood quality for large‐scale cultivation and utilization of eucalyptus wood as prime material.
Incremental identification of fluid multi‐phase reaction systems
Authors: Michalik Claas , Brendel Marc , Marquardt Wolfgang
Published: March 2009

Despite their importance, rigorous process models are rarely available for reaction and especially multi‐phase reaction systems. The high complexity of these systems, which is due to the superposed effects of mass transfer and intrinsic reaction, is the major barrier for the development of process models. A methodology that allows thesystematic decomposition of mass transfer and chemical reaction and thus enables the efficient identification of multi‐phase reaction systems is proposed in this work. The method is based on the so‐called Incremental Identification Method, recently presented by Brendel et al., Chem Eng Sci. 2006;61:5404‐5420. The method allows to easily test the identifiability of a system based on the available measurement data. If identifiability is given, the intrinsic reaction kinetics can be identified in a sound and numerically robust manner. These benefits are illustrated using a simulated 2‐phase enzyme reaction system. © 2009 American Institute of Chemical Engineers AIChE J, 2009
Palladium‐Catalyzed Three‐Component Cascade Cyclization Reaction of Bisallenes with Propargylic Carbonates and Organoboronic Acids: Efficient Construction of cis‐Fused Bicyclo[4.3.0]nonenes
Authors: Shu Wei , Jia Guochen , Ma Shengming
Published: March 2009

A bicycle built for two: The title reaction affords cis‐fused bicyclo[4.3.0]nonenes from readily available 1,5‐bisallenes with structurally diverse propargylic carbonates and arylboronic acids (see scheme; X=NTs, C(E1)2 with E1=CO2Bn, SO2Ph, dba=trans,trans‐dibenzylidenacetone). The reaction may involve a sequential oxidative addition, two different types of three carbopalladations, and a Suzuki‐type coupling.

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Physiological factors that regulate skin pigmentation
Authors: Yamaguchi Yuji , Hearing Vincent J.
Published: March 2009

More than 150 genes have been identified that affect skin color either directly or indirectly, and we review current understanding of physiological factors that regulate skin pigmentation. We focus on melanosome biogenesis, transport and transfer, melanogenic regulators in melanocytes, and factors derived from keratinocytes, fibroblasts, endothelial cells, hormones, inflammatory cells, and nerves. Enzymatic components of melanosomes include tyrosinase, tyrosinase‐related protein 1, and dopachrome tautomerase, which depend on the functions of OA1, P, MATP, ATP7A, and BLOC‐1 to synthesize eumelanins and pheomelanins. The main structural component of melanosomes is Pmel17/gp100/Silv, whose sorting involves adaptor protein 1A (AP1A), AP1B, AP2, and spectrin, as well as a chaperone‐like component, MART‐1. During their maturation, melanosomes move from the perinuclear area toward the plasma membrane. Microtubules, dynein, kinesin, actin filaments, Rab27a, melanophilin, myosin Va, and Slp2‐a are involved in melanosome transport. Foxn1 and p53 up‐regulate skin pigmentation via bFGF and POMC derivatives including α‐MSH and ACTH, respectively. Other critical factors that affect skin pigmentation include MC1R, CREB, ASP, MITF, PAX3, SOX9/10, LEF‐1/TCF, PAR‐2, DKK1, SCF, HGF, GM‐CSF, endothelin‐1, prostaglandins, leukotrienes, thromboxanes, neurotrophins, and neuropeptides. UV radiation up‐regulates most factors that increase melanogenesis. Further studies will elucidate the currently unknown functions of many other pigment genes/proteins. © 2009 International Union of Biochemistry and Molecular Biology, Inc.
Mg2+ ions bind at the C‐terminal region of skeletal muscle α‐tropomyosin
Authors: Corrêa Fernando , Farah Chuck S. , Salinas Roberto K.
Published: March 2009

Tropomyosin (Tm) is a dimeric coiled‐coil protein that polymerizes through head‐to‐tail interactions. These polymers bind along actin filaments and play an important role in the regulation of muscle contraction. Analysis of its primary structure shows that Tm is rich in acidic residues, which are clustered along the molecule and may form sites for divalent cation binding. In a previous study, we showed that the Mg2+‐induced increase in stability of the C‐terminal half of Tm is sensitive to mutations near the C‐terminus. In the present report, we study the interaction between Mg2+ and full‐length Tm and smaller fragments corresponding to the last 65 and 26 Tm residues. Although the smaller Tm peptide (Tm259‐284(W269)) is flexible and to large extent unstructured, the larger Tm220‐284(W269) fragment forms a coiled coil in solution whose stability increases significantly in the presence of Mg2+. NMR analysis shows that Mg2+ induces chemical shift perturbations in both Tm220‐284(W269) and Tm259‐284(W269) in the vicinity of His276, in which are located several negatively charged residues. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 583–590, 2009.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
The prevalence of cervical ribs in a London population
Authors: Brewin James , Hill Martin , Ellis Harold
Published: March 2009

Cervical ribs are an important cause of neurovascular compression at the thoracic outlet. Previous studies have shown the prevalence of cervical ribs to be between 0.05 and 3%, depending on the sex and race of the population studied. We examined 1,352 chest radiographs to determine the prevalence of cervical ribs in a London population of mixed sex and ethnicity. Our study found that the overall prevalence of cervical ribs was 0.74% with a higher rate in females compared with males (1.09 and 0.42%, respectively). Of the 10 individuals with a cervical rib, five were on the left, three were on the right and two were bilateral. The presence of elongated C7 transverse processes (transverse apophysomegaly) was also noted. We found a total of 30 elongated transverse processes with an overall prevalence of 2.21%. They were also more common in females (3.43%) than males (1.13%). Clin. Anat. 22:331–336, 2009. © 2009 Wiley‐Liss, Inc.
Involution of latent endometrial precancers by hormonal and nonhormonal mechanisms
Authors: Lin Ming‐Chieh , Burkholder Kyla A. , Viswanathan Akila N. , Neuberg Donna , Mutter George L.
Published: March 2009

BACKGROUND:

Inactivation of the PTEN suppressor gene has been shown to occur in the majority of endometrial cancer cases. Somatic PTEN inactivation by deletion and/or mutation, the first detectible change of endometrial carcinogenesis, has been reported to occur at a high frequency in the endometrium of normal premenopausal women, although few of these cases progress to cancer. It was hypothesized that the 50% to 60% reduced cancer risk attributed to oral contraceptives (OCPs) and intrauterine devices (IUDs) occurred in part through their activity as negative selection factors for these subclinical mutated glands.

METHODS:

A total of 71 women with a history of OCP use and 80 with a history of IUD use were age matched with 191 and 119 controls, respectively. Endometrial biopsy specimens were immunostained for PTEN, and each was scored for the presence or absence of PTEN‐null glands (latent precancer).

RESULTS:

The frequency of latent precancers was found to be significantly reduced in OCP‒exposed (13%; odds ratio [OR], 0.19 [P < .001]) and IUD‒exposed (18%; OR, 0.42 [P = .015]) women compared with respective matched controls (43% and 34%). The presence or absence of endometritis did not appear to be significantly correlated with PTEN status within the IUD‐exposed group (P = .24).

CONCLUSIONS:

Normal‐appearing PTEN mutated endometrial glands, which are highly prevalent in the normal population, may be targets of endometrial cancer risk‒modulating exposures. Some exposures reported to diminish the incidence of endometrial cancer in epidemiologic outcome studies, including OCP and IUD use, are associated with a proportionate decline in the frequency of latent precancers. Involution of pre‐existing endometrial latent precancers, as evaluated by PTEN analysis, may provide an accessible surrogate marker for long‐term endometrial cancer risk. Cancer 2009. © 2009 American Cancer Society.
Vertically aligned and interconnected nickel oxide nanowalls fabricated by hydrothermal route
Authors: Kumari L. , Li W. Z. , Vannoy C. H. , Leblanc R. M. , Wang D. Z.
Published: March 2009

Vertically aligned and well interconnected NiO nanowalls with thin nanodiscs of cubic NiO as the in situ formed building blocks were fabricated via a template‐free approach. The alkaline solution of ammonium hydroxide was used as a reductant and Ni foil as both source material and substrate for the nanowall synthesis. Surface morphology analysis confirmed the formation of 15 nm thick and 0.2–1.5 μm wide nanowalls. The nanowalls had the crystal structure of cubic NiO with their growth plane along the [111] direction. An optical band gap of about 3.8 eV for the NiO nanowalls was obtained from the optical absorption measurement. NiO nanowalls exhibited a broad UV emission band centered at around 390 nm. This simple, but efficient synthesis technique can facilitate the growth of well aligned 2D nanostructures with large surface area for possible applications in nanoscale devices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of 4‐Aminopyridinium‐4‐nitro phenolate single crystals
Authors: Babu G. Anandha , Thirupugalmani K. , Ramasamy P.
Published: March 2009

Organic optical material 4‐Aminopyridinium‐4‐nitro phenolate (4AP4NP) has been synthesized, and single crystals of size 20 x 14 x 6 mm3 have been grown from acetone solvent at room temperature by solvent evaporation technique. The grown crystals have been characterized by X‐ray diffraction to determine the cell parameters, and by FT‐IR technique to confirm the formation of the expected compound. The crystal belongs to monoclinic crystal system with space group P21/a.The structural perfection of the grown crystals has been analyzed by high‐resolution X‐ray diffraction (HRXRD) rocking curve measurements. The thermal stability of the compound has been determined by TG‐DTA curves. The transmittance of 4AP4NP has been used to determine the refractive index n; the extinction coefficient K and both the real εr and imaginary εi components of the dielectric constant as functions of photon energy. The optical band gap of 4AP4NP is 2.4 eV. The dielectric and mechanical behavior of the specimen was also studied. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Voluntary exercise and caloric restriction enhance hippocampal dendritic spine density and BDNF levels in diabetic mice
Authors: Stranahan Alexis M. , Lee Kim , Martin Bronwen , Maudsley Stuart , Golden Erin , Cutler Roy G. , Mattson Mark P.
Published: March 2009

Diabetes may adversely affect cognitive function, but the underlying mechanisms are unknown. To investigate whether manipulations that enhance neurotrophin levels will also restore neuronal structure and function in diabetes, we examined the effects of wheel running and dietary energy restriction on hippocampal neuron morphology and brain‐derived neurotrophic factor (BDNF) levels in db/db mice, a model of insulin resistant diabetes. Running wheel activity, caloric restriction, or the combination of the two treatments increased levels of BDNF in the hippocampus of db/db mice. Enhancement of hippocampal BDNF was accompanied by increases in dendritic spine density on the secondary and tertiary dendrites of dentate granule neurons. These studies suggest that diabetes exerts detrimental effects on hippocampal structure, and that this state can be attenuated by increasing energy expenditure and decreasing energy intake. Published 2009 Wiley‐Liss, Inc.
Genetic ablation of tenascin‐C expression leads to abnormal hippocampal CA1 structure and electrical activity in vivo
Authors: Gurevicius Kestutis , Kuang Fang , Stoenica Luminita , Irintchev Andrey , Gureviciene Irina , Dityatev Alexander , Schachner Melitta , Tanila Heikki
Published: March 2009

Despite evidence that the extracellular matrix glycoprotein tenascin‐C (TNC) is implicated in brain development and plasticity, its roles in the intact adult brain are unknown. Here we report that spontaneous local field potential (LFP) activity in freely moving adult TNC‐deficient mice is abnormal. The power of cortical and hippocampal theta and gamma oscillations was enhanced in comparison to wild‐type mice. The alteration in hippocampal gamma rhythm was subfield specific, such that CA1 gamma was accentuated while dentate gyrus gamma was normal. Similar to LFP, synaptic transmission and plasticity at perforant path synapses in the dentate gyrus were unaffected by the mutation. Morphological analyses revealed a subfield‐specific reduction in the CA1 volume and a reduction in the numbers of somatostatin‐positive interneurons in the hippocampus as potential structural substrates of the observed functional aberrations. These findings indicate a role for tenascin‐C in structural organization of the CA1 hippocampal subfield and in shaping neural activity. © 2009 Wiley‐Liss, Inc.
Mucin‐depleted foci show strong activation of inflammatory markers in 1,2‐dimethylhydrazine‐induced carcinogenesis and are promoted by the inflammatory agent sodium dextran sulfate
Authors: Femia Angelo Pietro , Dolara Piero , Luceri Cristina , Salvadori Maddalena , Caderni Giovanna
Published: March 2009

Mucin‐depleted foci (MDF), formed by dysplastic crypts devoid of mucins, have been identified in the colon of carcinogen‐treated rodents and in humans at high risk for colon cancer. The lack of the protective layer of mucus may cause inflammation which has been linked to colon carcinogenesis, therefore, the expression of markers such as cyclooxygenase‐2 (COX‐2), inducible nitric oxide synthase (i‐NOS) and macrophage infiltration was studied with immunohistochemistry (IH) in MDF harvested from F344 rats treated with the colon carcinogen 1,2‐dimethylhydrazine (DMH). The same determinations were performed in aberrant crypt foci (ACF) and, at a later time point, in tumours. A dramatic increase in COX‐2, i‐NOS and macrophage infiltration was observed in MDF but ACF showed a moderate increase compared with the paired normal mucosa. Tumours were positive for all the markers. RT‐PCR experiments demonstrated that i‐NOS RNA expression was increased in a set of MDF confirming the results obtained with immunohistochemistry. In an inflammation‐cancer experimental model [mice treated with azoxymethane (AOM) and dextran sodium sulphate (DSS)], we observed that DSS‐induced inflammation promoted MDF in a dose‐dependent manner, whereas ACF were not affected. In conclusion, we report here for the first time a strong activation of the inflammatory process in MDF, which may contribute to the further progression of MDF to tumours. © 2009 UICC
Culture of human mesenchymal stem cells using electrosprayed porous chitosan microbeads
Authors: Maeng Yu‐Jeong , Choi Sung‐Wook , Kim Hyun Ok , Kim Jung‐Hyun
Published: March 2009

The aim of this study was to fabricate porous chitosan microbeads using an electrospraying method into liquid nitrogen, then thawing and refreezing. The microbeads were then used to evaluate their potential for tissue engineering of human mesenchymal stem cells (hMSCs). Scanning electron microscopy (SEM) and a mercury porosimeter were used to show the morphology of the scaffolds formed and to determine their pore size and porosity. As the chitosan concentration increased (0.5, 1, 1.5, and 2 wt %), the diameter of the porous microbead increased from 350 to 890 μm, and the average pore size and the porosity decreased from 65 to 21 μm and 95 to 38%, respectively. The hMSCs were cultured onto the porous microbeads in a spinner flask. SEM images and methyl tetrazolium salt assays at 3, 7, 14, and 21 days of culture revealed that hMSCs had successfully attached and proliferated inside the porous microbeads. This study demonstrated that electrosprayed porous chitosan microbeads can be used as three‐dimensional scaffolds for tissue engineering. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res, 2010
Synthesis of tricyclic phospholene oxides by cycloaddition of phosphorus halides with heterocyclic analogs of 1‐vinyl‐3,4‐dihydronaphthalenes
Authors: Quin Louis D. , Gordon Michael D. , Macdiarmid Joan E.
Published: March 2009

Replacement of C‐4 with a hetero substituent (NR,O,S) in the 1‐vinyl‐3,4‐dihydronaphthalene system has provided a new type of diene for participation in the McCormack cycloaddition reaction with P(III) halides. The tricyclic phospholene oxides so obtained are the first to bear an additional heteroatom in the ring system. 1,2‐Dihydro‐7‐methoxy‐1‐(p‐toluenesulfonyl)‐4‐vinylquinoline is a stable solid that reacts with methylphosphonous dichloride to give, after hydrolysis of the cycloadduct, the 1,2,4,5‐tetrahydro‐1H‐phospholo‐[2,3‐c]quinoline ring system. The dihydroquinoline moiety was aromatized by detosylation with potassium t‐butoxide. The tendency of 4‐vinyl‐2H‐benzopyran to dimerize was a serious complication in its use, and the cycloaddition with methylphosphonous dichloride proceeded only in low yield. The product, a 2,3,3a,4‐tetra‐hydrobenzo[3,2‐d]pyran derivative, was a stable, easily purified and characterized substance. 4‐Vinyl‐2H‐benzo[b]thiopyran was more stable than the pyran, but the phospholo derivative from reaction with methylphosphonous dichloride was more difficult to purify. All products were characterized by 13C‐nmr spectroscopy.
Some reactions of mono substituted pyrazine monoxides
Authors: Ohta Akihiro , Watanabe Tokuhiro , Akita Yasuo , Yoshida Maki , Toda Suzumi , Akamatsu Tomoko , Ohno Hiroko , Suzuki Akiko
Published: March 2009

The reactions of the monoxides of propylpyrazine and phenylpyrazine with phosphoryl chloride or acetic anhydride were investigated. Except in the case of the reaction of 2‐propylpyrazine 1‐oxide with acetic anhydride, chlorination or acetoxylation occurred on the pyrazine ring in all cases; moreover, these reactions occurred preferentially at the position poorest in π‐electron density. The N‐oxidation and the successive chlorination of monochloro‐phenylpyrazines were also investigated, and the structures of the products were confirmed.
Reaction of α,β‐unsaturated ketones with guanidine. Substituent effects on the protonation constants of 2‐amino‐4,6‐diarylpyrimidines
Authors: Al‐Hajjar Farouk H. , Sabri Salim S.
Published: March 2009

1,3‐Diaryl‐2‐propen‐1‐ones, I, reacted with guanidine hydrochloride (II) in the presence of 3 moles of sodium hydroxide to give the corresponding 2‐amino‐4,6‐diarylpyrimidines, III. The structure and configuration of the products are based on chemical and spectroscopic evidence.

The protonation constants of these compounds (series A and series B) have been determined in 50 volume percent ethanol‐water medium. Excellent linear correlations are obtained when pKa values of the two series of 2‐amino‐4,6‐diarylpyrimidines, IIIa‐j and IIIk‐r, are plotted against the substituent constant, σx, and the polar substituent constant, σ* xC6H4, for substituted phenyl groups.

The pKa values have also been correlated with the extended Hammett equation. The correlation follows the equations:

Series A; pKa = 3.273 ‐ 0.820σI,X ‐ 0.662σR,X

Series B; pKa = 3.169 ‐ 0.424σI,X ‐ 0.137σR,X
6‐Aza und 7‐azacodeinone
Authors: Bös Michael , Fleischhacker Wilhelm , Kratzel Martin
Published: March 2009

Ausgehend von 1a werden durch Ringerweiterungsreaktionen neue N‐heterocyclische Codeinonderivative erhalten.
Synthesis of benzo[4,5]phenaleno[1,9‐bc]thiophene and benzo[4,5]phenaleno[9,1–6c]thiophene
Authors: Tominaga Yoshinori , Castle Raymond N. , Lee Milton L.
Published: March 2009

Two pentacyclic thiophenes, benzo[4,5]phenaleno[1,9–6c]thiophene (1) and benzo[4,5]phenaleno[9,1‐bc]‐thiophene (2) were synthesized via the corresponding 3‐methylphenanthro[2,1‐b]thiophene (7) and 1‐methylanthra[2,1–6]thiphene (19).
Synthesis of 2′‐amino‐2′‐deoxy‐5‐fluorocytidine
Authors: Sharma R. A. , Bloch A. , Bobek M.
Published: March 2009

Acetylation of 2′‐deoxy‐5‐fluoro‐2′‐trifluoroacetamidouridine with acetic anhydride in pyridine, followed by treatment with phosphorus pentasulfide in refluxing dioxane afforded 3′,5′‐di‐O‐acetyl‐2′‐deoxy‐5‐fluoro‐2′‐trifluorothioacetamido‐4‐thiouridine (3). Treatment of 3 with methanolic sodium methoxide furnished 2′‐deoxy‐2′‐trifluorothioacetamido‐4‐thiouridine (4), whereas its treatment with methanolic ammonia gave 2′‐amino‐2′‐deoxy‐5‐fluorocytidine (5). An alternative approach for the preparation of this compound proceeding from 2′‐trifluoroacetamidocytidine was unsuccessful, since the use of acetic anhydride in pyridine led to the replacement of the trifluoroacetyl function by an acetyl group, yielding an intermediate unsuitable for obtaining the target compound.

The title compound was inactive at 1 × 10−4 M concentration against HeLa and leukemia L1210 cells in vitro, but inhibited the in vitro growth of E. coli cells at a concentration of 1 × 10−7 M. It was also found to be a substrate for CR/dCR deaminase partially purified from human liver, with a Km of 128 μM.
Nichtsteroidale entzündungshemmer. 13. Bis‐(4‐methoxyphenyl)‐2‐arylthiopyrimidine
Authors: Klose Walter , Schwarz Katica
Published: March 2009

The synthesis of 4,5‐bis‐(4‐methoxyphenyl)‐2‐arylthio‐ and 4,6‐bis‐(4‐methoxyphenyl)‐2‐arylthiopyrimidines are described. The phenylthio, 4‐fluorophenylthio‐, 2‐thienylthio derivatives were prepared.
A novel synthesis of 2‐substituted oxazolines
Authors: Mundy Bradford P. , Kim Youseung
Published: March 2009

Thermal rearrangement of N‐acyl‐2‐oxazolidones in the presence of calcium oxide has been shown to provide a new entry into 2‐substituted oxazolines.
A simple and efficient synthesis of 3‐cyano‐4‐phenyl‐2‐pyridone
Authors: Marecki Paul E. , Wemple James N. , Butke Gregory P.
Published: March 2009

A preparatively useful method for the synthesis of 3‐cyano‐4‐phenyl‐2‐pyridone (I) is described. Reaction of 2‐cyano‐3‐methylcinnamamide (VII) with N,N‐dimethylformamide dimethyl acetal affords the corresponding dimethylaminomethylidene amide VIII which in turn, is thermally cyclized to I in DMF solvent. The advantages of this method include mild reaction conditions for short periods to give good yields of I on large scales without chromatographic purification.
The first example ot the benzo[b]pyrimido[4,5‐f]azocine king system
Authors: Schwan Thomas J. , Miles Nelson J.
Published: March 2009

Base catalyzed cyclization of ethyl 4‐[2‐(2‐amino‐4,5‐dimethoxyphenyl)ethyl]‐2‐phenylpyrimidine‐5‐carboxylate, derived from ethyl 4‐methyl‐2‐phenyl‐5‐pyrimidinecarboxylate and 3,4‐dimethoxy‐6‐nitrobenz‐aldehyde, gave 5,6‐dihydro‐8,9‐dimethoxy‐3‐phenylbenzo[b]pyrimido[4,5‐f]azocine‐12(11H)‐one, the first reported example of this ring system.
Aminopyrazoles. IV . Pyrazol‐3‐ and 5‐amines from 2,3‐dihaloalkanenitriles or 3‐chloroacrylonitriles and hydrazines
Authors: Ege Günter , Franz Hermann
Published: March 2009

2,3‐Dihalopropanenitriles and substituted 3‐chloropropenenitriles react with hydrazines in basic solution to form either pyrazol‐3‐amines 4 or pyrazol‐5‐amines 5 or a mixture of both isomers.
Photochemical approach to 4,5‐dioxoaporphine alkaloids. The total synthesis of pontevedrine
Authors: Castedo Luis , Estévez Ramón J. , Saá José M. , Suau Rafael
Published: March 2009

An easy and efficient total synthesis of pontevedrine 14b, a 4,5‐dioxoaporphine alkaloid, was achieved for the first time. It is based on the controlled photo‐oxidation of the lactam 7c, to give the benzylidene‐dioxo compound 13b and its subsequent photocyclizaton. A “one pot” transformation of the lactam 7c into norpontevedrine 14a was also achieved.
The reaction of 3‐(1‐imidazolyl)‐2‐alken‐1‐ones with nucleophiles
Authors: Kashima C. , Tajima T. , Shimizu M. , Omote Y.
Published: March 2009

Generally 3‐hetero‐substituted 2‐alken‐1‐ones were prepared from 1,3‐alkanediones, 3‐chloro‐2‐alken‐1‐ones, or conjugated ynones. The preparation of 3‐hetero‐substituted 2‐alken‐1‐ones was subjected to some limitations by these methods. By the reaction of 3‐(1‐imidazolyl)‐2‐alken‐1‐ones (I) and 3‐(3‐oxo‐1‐alkenyl)‐1‐methylimidazolium iodides (II) with nucleophiles, 3‐hetero‐substituted 2‐alken‐1‐ones could be obtained regioselectively in good yield under mild conditions. These results suggested that compounds I and II were concluded to be useful intermediates for the organic synthesis.
The regiospecific synthesis of N‐substituted pyrazoles. I. 1‐ and 2‐substituted indeno[1,2‐c]pyrazol‐4(1H)‐ones
Authors: Lemke Thomas L. , Sawhney Kailash N.
Published: March 2009

The reaction of the enaminoketones (2 or 5) of 2‐acyl‐1,3‐indandiones with unsymmetrical hydrazines results in the regiospecific synthesis of 1,3‐ or 2,3‐disubstituted indeno[1,2‐c]pyrazol‐4(1H)‐ones (4 or 7). The synthesis of the enaminoketones (2 or 5) is accomplished by way of amine addition to the 2‐acyl‐1,3‐indandiones 8a‐c or by reduction of the indenoisoxazole 9. The structural assignment of the isomeric indenopyrazoles 4 and 7 is based upon 1H‐nmr chemical shifts.
Chemistry of 1,6‐diazaphenalene. Reaction with alkylating and acylating agents
Authors: Avasthi Kamlakar , Cook J. M.
Published: March 2009

A study of the reactivity of 1,6‐diazaphenalene (1) toward alkylating and acylating agents has been carried out in order to investigate the chemistry of this new heterocycle. Attempts to alkylate 1 were successfully completed by stirring the lithium stabilized anion of 1 with either methyl iodide or benzyl bromide to provide N‐alkyldiazaphenalenes 4 and 5, respectively, whereas, experiments performed to alkylate 1 under conditions employed for alkylation of imidazole were unsuccessful. Studies directed toward acylation of 1 did not lead, in general, to isolable acyldiazaphenalenes; however, in one specific case successful acylation of 2‐chloro‐9‐methoxy‐1,6‐diazaphenalene (10) did provide a characterisable amide (14). Where possible the chemistry of 1,6‐diazaphenalene has been compared to that reported for imidazole.
Synthesis of 2,3,3a,8a‐tetrahydroindeno[2,1‐b]pyrrole derivatives
Authors: Crooks Peter A. , DeSimone Francesco , Ramundo Eliseo
Published: March 2009

A new entry into the 2,3,3a,8a‐tetrahydroindeno[2,1‐b]pyrrole system, 1, has been investigated. 2,3,3a,8a‐Tetrahydro‐3a,8a‐dihydroxy‐1‐methylindeno[2,1–6]pyrrole‐2,8‐dione, 3, formed from the reaction of ninhydrin and N‐methylacetamide has been subjected to catalytic hydrogenation, hydride reduction, and chlorination reactions to afford a variety of substituted derivatives of 1.