bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel HVPE technology to grow nanometer thick GaN, AlN, AlGaN layers and multi‐layered structures
Authors: Usikov Alexander , Shapovalova Lisa , Kovalenkov Oleg , Sukhoveev Vitali , Volkova Anna , Ivantsov Vladimir , Dmitriev Vladimir , Meng Fanyu , Datta Ranjan , Mahajan Subhash , Readinger Eric , Garrett Gregory , Wraback Michael , Reshchikov Michael
Published: June 2007

In this paper, we demonstrate new results on controllable HVPE growth of nitride materials with a deposition rate below 0.02 microns per minute and the first quantum size structures fabricated by HVPE. The nm‐scale layer thicknesses were verified by transmision electron microscopy (TEM) and photoluminescence (PL). Quantum well (QW) GaN/AlGaN and AlN/AlGaN structures have been grown by HVPE for the first time. Properties of the HVPE grown QWs are reported. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Correlation between the leakage current and the thickness of GaN‐layer of AlGaN/GaN‐HFET
Authors: Hinoki Akihiro , Kamiya Shinichi , Tsuchiya Tadayoshi , Yamada Tomoyuki , Kikawa Junjiroh , Araki Tsutomu , Suzuki Akira , Nanishi Yasushi
Published: June 2007

For further improvements in AlGaN/GaN heterojunction field‐effect transistor performance, it is necessary to reduce the buffer leakage current of the GaN layer. We studied the correlation between the buffer leakage current and the thickness of GaN layers. Unintentionally doped GaN layers with different thicknesses from 0.2 μm to 2 μm were grown by metal organic chemical vapor deposition on SiC substrates. The buffer leakage current of the GaN layer was measured after deposition of ohmic metal contact and the dislocations were observed using a transmission electron microscopy. The thinner samples had a smaller buffer leakage current although a higher density of threading dislocations. We discussed the origin for the reduction in the buffer leakage current for the thinner GaN layers by assuming that the residual carrier in the GaN layer was compensated by dislocations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐separation of thick two inch GaN layers grown by HVPE on sapphire using epitaxial lateral overgrowth with masks containing tungsten
Authors: Hennig Ch. , Richter E. , Weyers M. , Tränkle G.
Published: June 2007

Self‐separation of freestanding GaN layers of 50 mm diameter and thicknesses from around 50 µm to several hundred mm has been achieved using lateral overgrowth over silicon nitride masks with a high fraction of tungsten (WSiN). The moment of the separation was found to change with both the area ratio of the mask and the absolute structure size.
Reduction of threading dislocations in nonpolar 4H‐AlN on 4H‐SiC (11$ \bar 2 $0) grown by molecular‐beam epitaxy with slightly Al‐rich conditions
Authors: Horita M. , Suda J. , Kimoto T.
Published: June 2007

Growth of AlN on (11$ \bar 2 $0) 4H‐SiC a‐plane face substrates by molecular‐beam epitaxy has been investigated. Nonpolar (11$ \bar 2 $0) 4H‐AlN was isopolytypically grown on (11$ \bar 2 $0) 4H‐SiC substrates under slightly Al‐rich conditions. When growth was performed under slightly N‐rich conditions, (11$ \bar 2 $0) 2H‐AlN with high stacking fault density was obtained. A reduced density of defects such as stacking faults and threading dislocations was achieved by growing in slightly Al‐rich conditions. For the best sample, the stacking fault density was 2 × 105 cm–1, and the partial and perfect threading dislocation densities were 7 × 107 cm–2 and 1 × 107 cm–2, respectively.
Void assisted dislocation reduction in AlN and AlGaN by high temperature MOVPE
Authors: Balakrishnan K. , Iida K. , Bandoh A. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I.
Published: June 2007

Bridge layers of AlN and Al0.25Ga0.75N have been formed on linearly grooved substrates of 6H‐SiC by high temperature metal organic vapor phase epitaxy. Void assisted dislocation reduction was achieved in the formed bridge layers. Distinct difference in growth and coalescence behaviors of the Al0.25Ga0.75N layers was observed when the layers were grown on the substrates with grooves formed along 〈1$ \bar 1 $00〉 and 〈11$ \bar 2 $0〉 directions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of HVPE growth of freestanding c‐plane GaN layers using (100) γ‐LiAlO2 substrates
Authors: Richter E. , Hennig Ch. , Wang L. , Zeimer U. , Weyers M. , Tränkle G.
Published: June 2007

Freestanding c‐plane GaN substrates are obtained using (100) γ‐LiAlO2 substrates due to spontaneous separation during post‐growth cool down. It is shown that by growth optimization the structural properties of 200 µm thick freestanding GaN layers can be improved resulting in FWHM values of ω‐rocking curves below 400 arcsec for 002 and 302 reflection and threading‐dislocation densities below 109 cm–2. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InN clusters in InxGa1–xN quantum wells: analysis of bond lengths
Authors: Lei H. , Jiang X. J. , Chen J. , Belabbas I. , Ruterana P. , Nouet G.
Published: June 2007

In InxGa1–xN quantum wells, In‐N and Ga‐N bond lengths were analysed with a Stillinger‐Weber potential optimized for the III‐V nitride semiconductors. The Ga‐N and In‐N average bond lengths show a compressed state depending on the In concentration of the cluster.
Novel field plate structure of AlGaN/GaN HEMTs
Authors: Nakajima Akira , Shimizu Mitsuaki , Okumura Hajime
Published: June 2007

A novel FP structure, namely the floating field plate (FFP), is proposed to obtain a high breakdown voltage (VB) in AlGaN/GaN HEMTs. The FFP is characterized by electrically floating metals that are placed between the gate and drain electrodes beside a conventional field plate (FP). An optimization procedure for the FFP structure using an analytical model was investigated. Our numerical simulations yielded a VB value for the optimized FFP‐HEMTs of more than 2 kV, which is twice that of a conventional FP‐HEMT. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of hexagonal GaN films on the nitridated β‐Ga2O3 substrates using RF‐MBE
Authors: Ohira S. , Suzuki N. , Minami H. , Takahashi K. , Araki T. , Nanishi Y.
Published: June 2007

The growth of hexagonal GaN (h‐GaN) films on the nitridated β‐Ga2O3 substrates using radio‐frequency. molecular beam epitaxy (RF‐MBE) was investigated. The β‐Ga2O3 single crystal prepared by optical floating zone method was used to a substrate for GaN film growth, and nitridated by exposing to electron cyclotron resonance nitrogen plasma. It was found that h‐GaN layer is formed on the surface of β‐Ga2O3 substrates by controlling the nitridation condition, and homo‐epitaxial growth of h‐GaN films was succesfully achieved by optimizing the RF‐MBE growth condition. The observation of cross‐sectional high‐resolution transmission electron microscopy indicated that obtained GaN films grown on these nitridated β‐Ga2O3 substrates were of a high structural quality. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The surface diffusion of Ga species on an AlGaN facet structure in low pressure MOVPE
Authors: Narita Tetuso , Honda Yoshio , Yamaguchi Masahito , Sawaki Nobuhiko
Published: June 2007

The diffusion of Ga species in gas phase as well as on the surface are studied in selective area growth of AlGaN in low pressure metalorganic vapor phase epitaxy. The experiments were performed on a trapezoidal stripe with (0001) facet on the top and (1‐101) facet on the sides. It was found that the ridge growth on the facets were sensitive to the growth pressure, in agreement with numerical results. At a low pressure of 100 Torr, we got a uniform thickness of AlGaN alloy, but the alloy composition was not uniform. Exponential variation of the composition gave the effective diffusion length of Ga on the order of 0.7 μm which was independent of the growth pressure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication and characterization of transparent conductive Sn‐doped β‐Ga2O3 single crystal
Authors: Suzuki N. , Ohira S. , Tanaka M. , Sugawara T. , Nakajima K. , Shishido T.
Published: June 2007

Transparent conductive Sn‐doped β‐Ga2O3 single crystal with high crystallinity was successfully fabricated as a substrate for the growth of GaN‐based compounds. Sn‐doped β‐Ga2O3 single crystals were grown using a floating zone (FZ) method, and the properties of electrical conductivity, optical transmittance, and crystallinity were characterized to optimize the growth condition. It was found that these properties are controlled by the Sn doping concentration, and the specimen for 32 ppm Sn‐doped β‐Ga2O3 single crystal was optimized to satisfy these properties simultaneously, i.e. the substrate with the internal optical transmittance of above ∼85% in the visible region, the electrical resistivity of 4.27×10–2 Ωcm, the carrier density of 2.26×1018 cm–3, and the FWHM of X‐ray rocking curve of 43 arcsec was obtained. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adduct formation of CP2Mg with NH3 in MOVPE growth of Mg‐doped InN
Authors: Nagai Y. , Niwa H. , Hashimoto A. , Yamamoto A.
Published: June 2007

The Mg doping for MOVPE InN has been studied using biscyclopentadienyllmagnesium CP2Mg as a Mg source. The InN samples grown near the upstream end of the 18 cm long susceptor have very small grain size and contain a high level of C and H contamination. The XPS analysis of the deposits obtained by the supply of CP2Mg together with NH3 reveals that new Mg compounds are formed near the upstream end of the susceptor. The new compounds are adducts of CP2Mg and NH3, because they can not be formed when only CP2Mg is supplied. The adduct formation seems to be a cause for the very small grain size and the high levels of C and H contamination. The adduct formation is suppressed at positions with a distance more than 9 cm from the upstream end. This means that designs of reactor and susceptor are very important for successful Mg doping of InN with CP2Mg. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐step growth of InGaN quantum dots and application to light emitters
Authors: Yamaguchi T. , Dennemarck J. , Tessarek C. , Sebald K. , Gangopadhyay S. , Falta J. , Gutowski J. , Figge S. , Hommel D.
Published: June 2007

A two‐step growth method for creating InGaN quantum dots (QDs) was developed by using a combination of an InxGa1–xN nucleation layer (NL) without island structures and an InyGa1–yN formation layer (FL) with an indium content lower than that of the InxGa1–xN NL. The realization of QDs was confirmed by micro‐photoluminescence (μ‐PL) measurements only for the sample with both the InxGa1–xN NL and the InyGa1–yN FL. The spectral position of the QD ensemble recombination was controlled mainly by the deposition time of the InxGa1–xN NL. Green (∼520 nm) and amber (∼600 nm) LEDs with the QD layers grown by the two‐step growth method as the active region were also fabricated and compared with that having InGaN QW layers, reported previously. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of bulk aluminum nitride crystals
Authors: Helava H. , Davis S. J. , Huminic G. D. , Ramm M. G. , Avdeev O. V. , Barash I. S. , Chemekova T. Yu. , Mokhov E. N. , Nagalyuk S. S. , Roenkov A. D. , Segal A. S. , Vodakov Yu. A. , Makarov Yu. N.
Published: June 2007

We discuss the main growth issues for bulk AlN crystals: 1. durability of the crucible; 2. purity of the source; and 3. availability of large seeds. In situ‐prepared TaC crucibles and re‐crystallized powder sources are used in combination with SiC starting seeds to obtain high‐quality AlN bulk single crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of non‐stoichiometry and compensation on fundamental parameters of heavily‐doped InN
Authors: Shubina T. V. , Glazov M. M. , Ivanov S. V. , Vasson A. , Leymarie J. , Monemar B. , Araki T. , Naoi H. , Nanishi Y.
Published: June 2007

The empirical nearest‐neighbor tight binding theory and the Harrison bond‐orbital model are exploited to investigate the variation in effective band gap, electron effective masses and dielectric constants induced by non‐stoichiometry. A model is proposed to describe absorption edges in heavily‐doped InN using the Efros‐Shklovslii approach for compensated semiconductors and taking into account the non‐parabolicity of the InN band structure. Reasonable agreement with experimental trends has been demonstrated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence excitation spectroscopy of Er3+ ions in cubic GaN:Er
Authors: Glukhanyuk V. , Przybylińska H. , Kozanecki A.
Published: June 2007

In this paper we report the results of study of cubic GaN implanted with erbium by means of photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy. Only one optical emission center is observable at resonant excitation of Er3+ ions to 4I9/2 state. The positions of erbium energy levels were determined from the results of PL and PLE measurements for 4I15/2 and 4I9/2 state. Symmetry of energy levels has been assign according to group theory. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evaluation of AlGaN/GaN‐HFET with HfAlO gate insulator
Authors: Sazawa H. , Hirata K. , Kosaki M. , Shibata N. , Furuta K. , Yagi S. , Tanaka Y. , Kinoshita A. , Shimizu M. , Okumura H.
Published: June 2007

Metal‐insulator‐semiconductor (MIS) heterostructure field‐effect transistors (HFETs) fabricated with HfAlO as a gate insulator with high dielectric permittivity are demonstrated to achieve true enhancement‐mode operation with no gate leakage and high drain current density. Insertion of the HfAlO layer allows for forward gate bias voltages of up to +8 V without gate leakage (maximum gate current density of 1.2×10–5 mA/mm at +8 V gate bias) under direct current operation. Utilizing the extended forward gate bias swing, a maximum drain current density of 767 mA/mm is achieved, substantially higher than that of the non‐insulated HFET (427 mA/mm). A recessed‐gate MIS‐HFET with the HfAlO gate insulator exhibits a threshold voltage of +2.0 V and zero transconductance below a gate bias of +0.9 V, demonstrating true enhancement‐mode operation for the first time in recessed‐gate AlGaN/GaN‐HFETs with a maximum drain current density of 253 mA/mm at +5 V (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of substrate surface on GaN dot structure grown on Si(111) by droplet epitaxy
Authors: Otsubo Hiroaki , Kondo Toshiyuki , Yamamoto Yo , Maruyama Takahiro , Naritsuka Shigeya
Published: June 2007

The effect of substrate surface on GaN dot structure grown on Si(111) by droplet epitaxy using an rf plasma molecular beam epitaxy (MBE) system is reported. Compared with nitridated substrates, both enhancement of Ga migration and poorer wettability were observed on oxidized substrates, inducing enlargement of Ga droplets during nitridation. We demonstrated that the size and density of GaN dots grown by droplet epitaxy are strongly affected by pre‐treatment of the substrate. In the fabrication of GaN dots by droplet epitaxy, the importance of optimizing nitridation conditions according to the substrate surface is demonstrated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nitride‐organic semiconductor hybrid heterostructures for optoelectronic devices
Authors: Kim Hyunjin , Dang Cuong , Song Yoon‐Kyu , Zhang Qiang , Patterson William , Nurmikko A.V. , Kim K.‐K. , Song S.‐Y. , Han Jung
Published: June 2007

We explore hybrid gallium nitride‐organic semiconductors as composite layered thin film materials and report on initial results of fundamental studies of carrier transport across a junction composed of InGaN and selected organic thin films, with the eventual application goal towards versatile optoelectronic devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐color light emitting diode using polarization‐induced tunnel junctions
Authors: Grundmann Michael J. , Mishra Umesh K.
Published: June 2007

A multi‐color light emitting diode (LED) using two distinct active regions connected via a tunnel junction was grown by rf‐plasma‐assisted molecular beam epitaxy. The LED is contacted through n‐type layers, one of which provides efficient contact to a p‐type layer via a second tunnel junction. The tunnel junctions used in the structure use the high polarization fields found in the III‐nitrides material system to narrow the depletion width of the junction. Two peaks at 405 nm and 490 nm are observed in the electroluminescence spectrum of the LED, and current‐voltage characteristics indicate a turn‐on voltage of roughly 7.5 V and dynamic series resistance of 19 Ω at 80 mA for a 300 μm square device. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the elemental composition of trace analytes in complex matrices using exact masses of product ions and corresponding neutral losses
Authors: Kaufmann Anton
Published: June 2007

The emergence of time‐of‐flight (TOF) and hybrid quadrupole/time‐of‐flight (Q‐TOF) mass spectrometers has offered new possibilities for determining the elemental composition of analytes present at trace levels. The mass accuracy provided by these instruments is currently in the range of 2–5 m m/z units, permitting the determination of the elemental composition of small molecules. The orthogonal information of relative isotopic abundances (RIAs) is used to reduce the number of elemental compositions that are possible, based on consideration of exact masses. Elimination of additional possible compositions has been reported when the analyte is fragmented and its resulting product ions and corresponding neutral losses are carefully analyzed. Published algorithms reduce the number of proposed precursor ions by deleting each precursor candidate which cannot be explained by summing any combination of postulated product ion and corresponding neutral loss elemental composition candidates. An extension of such algorithms is described in this paper. This approach compares not only the precursor ion with the different fragments, but tests the possible descent of any ion from all other recorded ions. This extended algorithm has been tested by processing published data. Algorithms analyzing product ion spectra can be used for real‐life data. However, there is a risk that an ion which originates from the mobile phase or from a co‐eluting matrix compound can be mathematically correlated to the investigated precursor ion. Such an incorrect correlation can lead to the deletion of a correct elemental composition. This is an important issue if TOF rather than Q‐TOF instruments are used. Therefore, ultra‐performance liquid chromatography (UPLC) and a peak deconvolution algorithm were used to generate and process TOF chromatograms in order to minimize the number of ions which are not related to the analyte precursor ion. The combined use of chromatographic deconvolution and product ion spectra has been tested and is critically discussed. Copyright © 2007 John Wiley & Sons, Ltd.
Development of a sensitive and specific liquid chromatography/mass spectrometry method for the determination of tenofovir in human plasma
Authors: Bennetto‐Hood Chantelle , Long Mary C. , Acosta Edward P.
Published: June 2007

A sensitive and specific method for the quantitation of tenofovir (TFV) in human plasma by liquid chromatography/electrospray ionization mass spectrometry was developed and validated. Plasma samples were prepared by solid‐phase extraction performed on Waters Oasis cation‐exchange cartridges (30 mg). Chromatographic separation was performed isocratically on a reversed‐phase Waters Atlantis dC18 column (2.0 × 100 mm, 3 µm). The mobile phase consisted of a hydroxylamine/acetic acid buffer (pH 6.75) and methanol (93:7, v/v). The acquisition was performed in selected ion monitoring mode for the protonated molecular ions [M+H]+ of m/z 288.2 for TFV and 212.2 for the internal standard, zalcitibine. The method was fully validated to determine its specificity, recovery, linearity and sensitivity, accuracy and precision. The analytical range was set at 1–750 ng/mL using a 200 µL plasma sample, with a mean coefficient of determination (r2) of 0.9969. The mean accuracies for the calibration standards ranged from −5.0 to 4.3%, while the precisions were within 1.2 and 6.4%. Intra‐assay and inter‐assay mean accuracies for three quality control concentrations (2, 60, and 600 ng/mL) ranged from −6.1 to 10.7%, while the precisions were within 1.3 and 9.1%. TFV was shown to be stable under normal storage and assay conditions; no degradation was seen when stored at −20°C or −80°C for up to 6 months, and after 16 h at room temperature in the injection matrix. The present method provides an accurate, precise, and sensitive tool for TFV quantitation and was successfully applied to an external proficiency‐testing program and pharmacokinetic analysis. Copyright © 2007 John Wiley & Sons, Ltd.
Improved method for the simultaneous determination of d4T, 3TC and ddl intracellular phosphorylated anabolites in human peripheral‐blood mononuclear cells using high‐performance liquid chromatography/tandem mass spectrometry
Authors: Becher François , Pruvost Alain , Goujard Cécile , Guerreiro Catherine , Delfraissy J.‐F. , Grassi Jacques , Benech Henri
Published: June 2007

The original article to which this Erratum refers was published in Rapid Commun Mass Spectrom. 2002; 16: 555–565.
New estimates of the prevalence of neurological and sensory sequelae and mortality associated with congenital cytomegalovirus infection
Authors: Dollard Sheila C. , Grosse Scott D. , Ross Danielle S.
Published: June 2007

Congenital CMV is a major cause of neurological and sensory impairment in children. Reliable estimates of the prevalence of permanent sequelae and mortality associated with congenital CMV are needed to guide development of education and prevention programmes and to gauge the financial costs associated with this disease. To calculate such estimates, this review used data solely from studies in which children with congenital CMV were identified through universal screening. Based on 15 studies with a total of 117 986 infants screened, the overall CMV birth prevalence estimate was 0.7%. The percentage of infected children with CMV‐specific symptoms at birth was 12.7%. The percentage of symptomatic children with permanent sequelae was 40–58%. The percentage of children without symptoms at birth who developed permanent sequelae was estimated to be 13.5%. The true burden of congenital CMV infection is unclear because data on important outcomes, such as visual impairment, are lacking and follow‐up of infected children has been too short to fully identify late‐onset sequelae. Therefore, the estimates of permanent sequelae associated with congenital CMV presented here are likely underestimates. Future studies should extend follow‐up of CMV‐infected children identified through universal screening and include the evaluation of visual impairment. Copyright © 2007 John Wiley & Sons, Ltd.
The phase transition in inhomogeneous random graphs
Authors: Bollobás Béla , Janson Svante , Riordan Oliver
Published: June 2007

The “classical” random graph models, in particular G(n,p), are “homogeneous,” in the sense that the degrees (for example) tend to be concentrated around a typical value. Many graphs arising in the real world do not have this property, having, for example, power‐law degree distributions. Thus there has been a lot of recent interest in defining and studying “inhomogeneous” random graph models.

One of the most studied properties of these new models is their “robustness”, or, equivalently, the “phase transition” as an edge density parameter is varied. For G(n,p), p = c/n, the phase transition at c = 1 has been a central topic in the study of random graphs for well over 40 years.

Many of the new inhomogeneous models are rather complicated; although there are exceptions, in most cases precise questions such as determining exactly the critical point of the phase transition are approachable only when there is independence between the edges. Fortunately, some models studied have this property already, and others can be approximated by models with independence.

Here we introduce a very general model of an inhomogeneous random graph with (conditional) independence between the edges, which scales so that the number of edges is linear in the number of vertices. This scaling corresponds to the p = c/n scaling for G(n,p) used to study the phase transition; also, it seems to be a property of many large real‐world graphs. Our model includes as special cases many models previously studied.

We show that, under one very weak assumption (that the expected number of edges is “what it should be”), many properties of the model can be determined, in particular the critical point of the phase transition, and the size of the giant component above the transition. We do this by relating our random graphs to branching processes, which are much easier to analyze.

We also consider other properties of the model, showing, for example, that when there is a giant component, it is “stable”: for a typical random graph, no matter how we add or delete o(n) edges, the size of the giant component does not change by more than o(n). © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 31, 3–122, 2007
Shrinkage of de Morgan formulae under restriction
Authors: Paterson Michael S. , Zwick Uri
Published: June 2007

It is shown that a random restriction leaving only a fraction ϵ of the input variables unassigned reduces the expected de Morgan formula size of the induced function by a factor ofO(E(5−√2)/2) =O(ϵ1.63). (A de Morgan, or unate, formula is a formula over the basis {∧, ∨, ¬}.) This improves a long‐standing result ofO(ϵ1.5) by Subbotovskaya and a recent improvement toO(ϵ(21−√73)/8) =O(ϵ1.55) by Nisan and Impagliazzo. The New exponent yields an increased lower bound ofn(7−√3)/2−o(1)= Ω(n2.63) for the de Morgan formula size of a function in P defined by Andreev. This is the largest formula size lower bound known, even for functions in NP. © 1993 John Wiley & Sons, Inc.
Long range percolation in stationary point processes
Authors: Burton Robert M. , Meester Ronald W. J.
Published: June 2007

We consider a continuum percolation model in ℝd, d ⩾ 1 in which any two points of a stationary point process are connected with a probability which decays exponentially in the distance between the points. We give sufficient conditions for the (non)‐existence of a phase transition. We also give examples of processes which show that it is impossible to write down a theorem which relates the critical parameter value of a process to its density. Finally, we show that uniqueness of the infinite cluster is still valid in this general setting. © 1993 John Wiley & Sons, Inc.
A probabilistic analysis of a pattern matching problem
Authors: Atallah Mikhail J. , Jacquet Philippe , Szpankowski Wojciech
Published: June 2007

The study and comparison of strings of symbols from a finite or an infinite alphabet is relevant to various areas of science, notably molecular biology, speech recognition, and computer science. In particular, the problem of finding the minimum “distance” between two strings (in general, two blocks of data) is of a practical importance. In this article we investigate the (string) pattern matching problem in a probabilistic framework, namely, it is assumed that both strings form an independent sequences of i.i.d. symbols. Given a text stringaof lengthnand a pattern stringbof lengthm, letMm,nbe the maximum number of matches betweenband allm‐substrings ofa. Our main probabilistic result shows that for a wide range of input parametersin probability (pr.) providedm, n→∞ such that logn=o(m), wherePis the probability of a match between any two symbols of these strings, andTis the probability of a match between two positions in the text string and a given position of the pattern string. We also prove thatMm,n/m→P almost surely(a.s.) for logn=o(m). © 1993 John Wiley & Sons. Inc.
Radius and diameter of random subgraphs of the hypercube
Authors: Kostochka A. V. , Sapozhenko A. A. , Weber K.
Published: June 2007

Let Gn = (Vn, En) be the random subgraph of the n‐cube graph Qn produced as follows: Vn is randomly sampled from the vertex set of Qn so that E{x ∈Vn} = pv independently for each vertex x ∈Qn. Then En is randomly sampled from the set of edges induced by Vn in Qn so that P{(x, y) ∈ En} = pe independently for each induced edge (x, y). Let Pv and pe be fixed probabilities such that 0 < p = pvpe ⩽ 1 and mp = [−1 /log2(1 − p)]. We show that for the radius R(Gn) and the diameter D(Gn) of the main component of Gn almost surely the following inequalities hold magnified image. © 1993 John Wiley & Sons, Inc.
Random graphs with monochromatic triangles in every edge coloring
Authors: Rödl Vojtech , Ruciński Andrzej
Published: June 2007

We prove that for every r ⩾ 2 there is C > 0 such that if p Cn−1/2 then almost surely every r‐coloring of the edges of the binomial random graph K(n, p) results in a monochromatic triangle. © 1994 John Wiley & Sons, Inc.
Random walks on colored graphs
Authors: Condon Anne , Hernek Diane
Published: June 2007

We initiate a study of random walks on undirected graphs with colored edges. In our model, a sequence of colors is specified before the walk begins, and it dictates the color of edge to be followed at each step. We give tight upper and lower bounds on the expected cover time of a random walk on an undirected graph with colored edges. We show that, in general, graphs with two colors have exponential expected cover time, and graphs with three or more colors have doubly‐exponential expected cover time. We also give polynomial bounds on the expected cover time in a number of interesting special cases. We described applications of our results to understanding the dominant eigenvectors of products and weighted averages of stochastic matrices, and to problems on time‐inhomogeneous Markov chains. © 1994 John Wiley & Sons, Inc.
Grids in random graphs
Authors: Fernandez de la Vega W. , Manoussakis Y.
Published: June 2007

Threshold probabilities for the existence in a random graph on n vertices of a graph isomorphic to a given graph of order Cn and average degree at least three are investigated. In particular it is proved that the random graph G(n, p) on n vertices with edge probability contains a square grid on En/2 vertices. © 1994 John Wiley & Sons, Inc.
Note on the heights of random recursive trees and random m‐ary search trees
Authors: Pittel Boris
Published: June 2007

A process of growing a random recursive tree Tn is studied. The sequence {Tn} is shown to be a sequence of “snapshots” of a Crump–Mode branching process. This connection and a theorem by Kingman are used to show quickly that the height of Tn is asymptotic, with probability one, to c log n. In particular, c = e = 2.718 … for the uniform recursive tree, and c = (2γ)−1, where γe1+γ = 1, for the ordered recursive tree. An analogous reduction provides a short proof of Devroye's limit law for the height of a random m‐ary search tree. We show finally a close connection between another Devroye's result, on the height of a random union‐find tree, and our theorem on the height of the uniform recursive tree. © 1994 John Wiley & Sons, Inc.
Almost all regular graphs are hamiltonian
Authors: Robinson R. W. , Wormald N. C.
Published: June 2007

In a previous article the authors showed that almost all labelled cubic graphs are hamiltonian. In the present article, this result is used to show that almost all r‐regular graphs are hamiltonian for any fixed r ⩾ 3, by an analysis of the distribution of 1‐factors in random regular graphs. Moreover, almost all such graphs are r‐edge‐colorable if they have an even number of vertices. Similarly, almost all r‐regular bipartite graphs are hamiltonian and r‐edge‐colorable for fixed r ⩾ 3. © 1994 John Wiley & Sons, Inc.
Random sparse unary predicates
Authors: Shelah Saharon , Spencer Joel
Published: June 2007

Random unary predicates U on [n] holding with probability p are examined with respect to sentences A in a first‐order language containing U and “less than.” When p = p(n) satisfies nk+1 ≪ 1 ≪ npk it is shown that Pr[A] approaches a limit dependent only on k and A. In a similar circular model the limit is shown to be zero or one. © 1994 John Wiley & Sons, Inc.
Unlabeled trees: Distribution of the maximum degree
Authors: Goh William M. Y. , Schmutz Eric
Published: June 2007

Pick a tree uniformly at random from among all unlabeled trees on n vertices, and let Xn be the maximum of the degrees of its vertices. For any fixed integer d,
magnified image
as n→∞, where μn = c1 log n, where {μn} : = μn – ⌊μ⌋ denotes the fractional part of μn and where co, c1, and η∞ are knnown constants, givenb approximately by c0 = 3.262 …, c1 = 0.9227 …, and η∞ = 0.3383…. © 1994 John Wiley & Sons, Inc.
Low‐diameter graph decomposition is in NC
Authors: Awerbuch Baruch , Berger Bonnie , Cowen Lenore , Peleg David
Published: June 2007

We obtain the firstNCalgorithm for the low‐diameter graph decomposition problem on arbitrary graphs. Our algorithm runs inO(log5(n)) time, and usesO(n2) processors. © 1994 John Wiley & Sons, Inc.
A probably fast, provably optimal algorithm for rectilinear Steiner trees
Authors: Deneen Linda L. , Shute Gary M. , Thomborson Clark D.
Published: June 2007

We use the technique of divide‐and‐conquer to construct a rectilinear Steiner minimal tree on a set of sites in the plane. A well‐known optimal algorithm for this problem by Dreyfus and Wagner [10] is used to solve the problem in the base case. The run time of our optimal algorithm is probabilistic in nature: for all ϵ > 0, there exists b > 0 such that Prob[T(n) > 2b√n log n]>1–ϵ, for n log n > 1 – ϵ, for n sites uniformly distributed on a rectangle. The key fact in the run‐time argument is the existence of probable bounds on the number of edges of an optimal tree crossing our subdivision lines. We can test these bounds in low‐degree polynomial time for any given set of sites. © 1994 John Wiley & Sons, Inc.
Near‐perfect token distribution
Authors: Broder A. Z. , Frieze A. M. , Shamir E. , Upfal E.
Published: June 2007

Suppose that n tokens are arbitrarily placed on the n nodes of a graph. At each parallel step one token may be moved from each node to an adjacent node. An algorithm for the near‐perfect token distribution problem redistributes the tokens in a finite number of steps, so that, at the end, no more than O(1) tokens reside at each node. (In perfect distribution, at the end, exactly one token resides at each node.) In this paper we present a simple algorithm that works for all extrovert graphs, a new property which we define and study. In terms of connectivity requirements, extrovert graphs are roughly in‐between expanders and compressors. Our results lead to an optimal solution for the near‐perfect token distribution problem on almost all cubic graphs. The new solution is conceptually simpler than previous algorithms, and applies to graphs of minimum possible degree. © 1994 John Wiley & Sons, Inc.
Improved upper bounds for the critical probability of oriented percolation in two dimensions
Authors: Balister Paul , Bollobás Béla , Stacey Alan
Published: June 2007

We refine the method of our previous paper [2] which gave upper bounds for the critical probability in two‐dimensional oriented percolation. We use our refinement to show that

© 1994 John Wiley & Sons, Inc.
Lower bounds for a subexponential optimization algorithm
Authors: Matoušek Jiří
Published: June 2007

Recently Sharir and Welzl described a randomized algorithm for a certain class of optimization problems (including linear programming), and then a subexponential bound for the expected running time was established. We give an example of an (artificial) optimization problem fitting into the Sharir–Welzl framework for which the running time is close to the upper bound, thus showing that the analysis of the algorithm cannot be much improved without stronger assumptions on the optimization problem and/or modifying the algorithm. Further we describe results of computer simulations for a specific linear programming problem, which indicate that “one‐permutation” and “move‐to‐front” variants of the Sharir–Welzl algorithm may sometimes perform much worse than the algorithm itself. © 1994 John Wiley & Sons, Inc.
A shuffle that mixes sets of any fixed size much faster than it mixes the whole deck
Authors: Pemantle Robin
Published: June 2007

Consider an n by n array of cards shufled in the following manner. An element x of the array is chosen uniformly at random. Then with probability 1/2 the rectangle of cards above and to the left of x is rotated 180deg;, and with probability 1/2 the rectangle of cards below and to the right of x is rotated 180°. It is shown by an eigenvalue method that the time required to approach‐ the uniform distribution is between n2/2 and cn2 in n for some constant c. On the other hand, for any k it is shown that the time needed to uniformly distribute a set of cards of size k is at most c(k)n, where c(k) is a constant times k3 In(k)2. This is established via coupling; no attempt is made to get a good constant. © 1994 John Wiley & Sons, Inc.
Modified Corn Starches with Improved Comprehensive Properties for Preparing Thermoplastics
Authors: Zhang Shui‐Dong , Zhang Yu‐Rong , Zhu Jiang , Wang Xiu‐Li , Yang Ke‐Ke , Wang Yu‐Zhong
Published: June 2007

A novel method of starch modification was developed to obtain thermoplastic starch plastics with improved comprehensive properties. Corn starch was oxidized under mild conditions using sodium periodate to prepare dialdehyde starch, which had an acceptable average molecular weight. The dialdehyde starch with 35.2% carbonyl content was reacted with different alcohols (methanol, ethanol, and glycol) to prepare a series of novel starch derivatives, whose structures were characterized by 1H‐NMR and FT‐IR. The thermogravimetric analysis showed that these starch derivatives had an improved thermal stability compared with dialdehyde starch. Thermoplastic starch and its derivatives were prepared when water and glycerol were added as plasticizers. The modified thermoplastic starch and its derivatives had better mechanical properties than other modified starches, and lower humidity absorption than conventional thermoplastic starches. The highest tensile strength and elongation at break reached 17.5 MPa and 149%, respectively, and the highest humidity absorption was about 37%.
Correlations of the Composition, Minerals, and RVA Pasting Properties of Various Potato Starches
Authors: Zaidul I. S. Md. , Norulaini Nik , Omar A. K. Mohd. , Yamauchi Hiroaki , Noda Takahiro
Published: June 2007

Multiple linear regression equations were developed to correlate the granule size distribution, composition, and minerals content with the Rapid Visco Analyser (RVA) pasting properties of potato starches of different cultivars. From the experimental values and the values of the regression coefficients, it could be observed that a higher level of amylose resulted in a lower peak viscosity (PV) and breakdown (BD) and higher setback (SB) and peak viscosity temperature (PVT) in the potato starches. The reverse was observed when the phosphorus content was higher. Smaller granule size was associated with a decrease in the PVT, whereas larger granules demonstrated higher PV, BD, and SB values in the potato starches. A higher calcium content was associated with a decrease in PV and an increase in BD, SB, and PVT. On the other hand, higher potassium was associated with an increase in PV, BD, SB, and PVT. The sodium contents demonstrated a higher PV and SB, and the reverse was observed in the BD and PVT. It is difficult to conclude the precise role of magnesium ions to the RVA properties although as divalent cations, they may have similar effect as calcium. From the positive and negative values of the regression coefficients it was shown that the correlation is useful for determining more precise values of the RVA pasting properties using a multiple linear regression equation. The correlations were also useful for predicting the effects of the starch composition and minerals on the RVA pasting properties.
Starch Characterisation of Araucaria angustifolia and Araucaria araucana Seeds
Authors: Conforti Paula A. , Lupano Cecilia E.
Published: June 2007

Araucaria angustifolia and Araucaria araucana are conifers that cover different areas of South America. Their seeds have been consumed from prehistoric times until today in Brazil, Argentina and Chile. In this work, the starch of Araucaria angustifolia and Araucaria araucana seeds were analysed by light and environmental scanning electron microscopy, X‐ray diffraction, and differential scanning calorimetry. The starch granules of A. angustifolia and A. araucana were round or slightly oval, with a central hilum. Both starches gave X‐ray diffraction patterns compatible with the A‐type, with strong peaks at 15°, 17°, and 23°. The gelatinisation temperature of A. angustifolia starch (68.5°C) was higher than that of A. araucana (66.6°C), probably due to the higher amylose content of the former (22.4 % and 17.3 %, respectively). The thermograms of A. araucana starch presented a minor peak at about 71°C, which was attributed to the fact that the starch granules population of A. araucana was heterogeneous, with large and small granules, whereas A. angustifolia starch contained mainly large granules.
Evaluation of bit error rate for packet combining with constellation rearrangement
Authors: Benjillali Mustapha , Szczecinski Leszek , Aïssa Sonia , Gonzalez Cristian
Published: June 2007

In this paper, we propose a method for evaluation of the bit error rate (BER) for packet combining based on constellation rearrangement (CoRe). Such mapping diversity scheme, adopted in the high speed downlink packet access (HSDPA), uses Gray‐mapped constellations and is based on suboptimal accumulation of the reliability metrics generated in each of the transmissions. We present an exact model for the logarithmic likelihood ratios (LLR) obtained by means of the so‐called max‐log approximation, and we show that their conditional probability density functions (pdf) are piecewise Gaussian. We then present the derivation of the uncoded BER and illustrate it with simulation results that confirm our formulation. Finally, we propose simplifications which significantly reduce the complexity of the evaluation method and provide results with a very good accuracy; an extension to transmissions over faded channel is also presented. Copyright © 2007 John Wiley & Sons, Ltd.
Crisis residential treatment: An alternative to hospitalization
Authors: Fields Steven , Weisman Gilbert K.
Published: June 2007

Alternatives to psychiatric hospitalization include such programs as La Posada in San Francisco—a cost‐effective model of crisis residential treatment that combines crisis intervention with therapy.
Emergency psychiatric evaluation of „organic”︁ mental disorders
Authors: Allen Michael H. , Fauman Michael A. , Morin Stephen F. X.
Published: June 2007

The emergency psychiatrist must first differentiate abnormal behavior with a medical etiology from that caused by so‐called junctional processes. Delays in diagnosis can be catastrophic and make a compelling argument for physician involvement in emergency mental health care.
Psychological treatments in the psychiatric emergency service
Authors: Rosenberg Ronald C.
Published: June 2007

A survey of psychological techniques that have been applied in the psychiatric emergency service demonstrates their potential for meeting the increased treatment demands of this changing and challenging milieu.
Emergency pharmacotherapy: The evolving role of medications in the emergency department
Authors: Ellison James M. , Pfaelzer Christine
Published: June 2007

The dual roles of psychiatric medications in the emergency department are reviewed; established and new approaches to the pharmacotherapy of acute behavioral changes are described.
Frustration or opportunity? The impact of managed care on emergency psychiatry
Authors: Schuster James M.
Published: June 2007

The positive and negative effects of managed care on emergency psychiatry are reviewed, as are potential opportunities for emergency psychiatry in the new health care environment.
Academic issues in emergency psychiatry
Authors: Thienhaus Ole J.
Published: June 2007

The psychiatric emergency service is attracting increasing attention as a setting in which to carry out academic psychiatry's mission of educating tomorrow's leaders in the field of clinical psychiatry and of conducting services and clinical research.
The development of group process in treatment with mental patients
Authors: Fairweather George W.
Published: June 2007

There was little evidence to indicate that groups of individuals who had been diagnosed as mentally ill—particularly those who had been confined to a hospital for any length of time—could organize themselves into self‐functioning groups, much less operate a small, business‐oriented society.
From clinician to manager
Authors: Ewalt Patricia L.
Published: June 2007

New skills must be learned and a new self‐image must be developed by a clinician who assumes a middle management role for the first time.
How can we manage divided houses?
Authors: Kouzes James M. , Mico Paul R.
Published: June 2007

When the organizations in which people work produce natural conflict and disjunction, middle managers need a view of the world which is fundamentally different from that presented in theories derived from observing stable and mechanistic organizations.
Resistance of mental health professionals to working with the chronic mentally ill
Authors: Minkoff Kenneth
Published: June 2007

Among mental health professionals, the prevailing attitude is that working with chronic patients is unrewarding, nonprestigious, and hopeless. Consequently, our efforts to overcome barriers to the care of the chronic mentally ill will never be successful unless we focus on professionals' resistance to working with these patients.
Evolution of mental health services and areas for change
Authors: Mechanic David
Published: June 2007

Appropriate care for the most seriously mentally disabled will require an improved framework for public‐sector services, Medicaid reforms, systems of managed care, and effective advocacy.
Issues in case management for the chronically mentally ill
Authors: Dill Ann E. P.
Published: June 2007

Case managers must balance the interests of the service delivery system with the demands of their relationships with clients. This dual allegiance has problematic consequences for the design and practice of case management for the chronically mentally ill.
Substituted judgment and protective intervention
Authors: Crystal Stephen , Dejowski Edmund
Published: June 2007

To avoid reinstitutionalization of judgment‐impaired individuals, community mental health needs to build its capacity for serving uncooperative persons who face high risks of physical or environmental harm.
The political context of mental health care
Authors: Rochefort David A.
Published: June 2007

A political perspective offers useful insights into the origins, Organization, and impact of contemporary mental health programs. It also suggests approaches for improved advocacy, management, and delivery of services.
Financing care for the seriously mentally ill
Authors: Rubin Jeffrey
Published: June 2007

Because the structure of financing options for the care of the seriously mentally ill affects the patterns of care received, mental health care reform must begin with changes to the financing structures.
The chemically dependent physician: Clinical and legal considerations
Authors: Angres Daniel H. , Busch Katie A.
Published: June 2007

The medical community has made great advances in recognizing chemical dependence in the physician community. However, difficulties remain in terms of the clinician treating this disease and maintaining a liaison between legal and clinical aspects.
Sexual abuse of patients by therapists: Strategies for offender management and rehabilitation
Authors: Gartrell Nanette , Herman Judith , Olarte Silvia , Feldstein Michael , Localio Russell , Schoener Gary
Published: June 2007

Many therapists are unsure of how to respond to reports of sexual abuse of patients by previous therapists. The results of strategies developed in Minnesota and other jurisdictions suggest ways to handle the reporting, Management, and rehabilitation of offenders in therapist‐patient sexual abuse cases.