bluuebunny/crossref_metadata_2025 huggingface dataset:
Erhalt und Förderung der Selbstständigkeit bei Pflegeheimbewohnern
Authors: Ackermann Andreas , Oswald W.D.
Published: September 2006

Auch bei bereits eingetretener Pflegebedürftigkeit sind Maßnahmen der Rehabilitation zur Vermeidung eines Fortschreitens der Erkrankung oder der Verschlimmerung einer Behinderung zu gewähren. Zeitlich begrenzte stationäre wie ambulante Rehabilitationsmaßnahmen nach SGB V sind bei Pflegeheimbewohnern jedoch oftmals nicht sinnvoll, zumal eine nachhaltige Wirkung meist nicht erzielt werden kann. Für Pflegeheimbewohner sind langfristig angelegte rehabilitative Maßnahmen vor dem Hintergrund einer aktivierenden Pflege angebracht. Das Forschungsprojekt “Rehabilitation im Altenpflegeheim” untersucht die Anwendbarkeit und Effektivität eines auf Grundlage bestehender Rehabilitations- und Aktivierungsmaßnahmen beruhenden rehabilitativen Interventionsansatzes bei einer Pflegeheimklientel. In diesem Übersichtsartikel werden vor dem Hintergrund der theoretischen Grundlagen einer aktivierend-rehabilitativen Pflege, die als Basis aller interventionistischer Bemühungen in der stationären Altenhilfe angesehen werden kann, existierende therapeutisch-rehabilitative Ansätze für Pflegeheimbewohner dargestellt und anhand der vorliegenden Literatur diskutiert.
Gedächtnissprechstunden in Süddeutschland
Authors: Buschert Verena
Published: September 2006

Ergebnisse der telefonischen Befragung von 33 unterschiedlich organisierten Gedächtnissprechstunden (GS) in Süddeutschland (PLZ 7, 8 und 9) zeigen ein weitgehend einheitliches Vorgehen bei der Diagnostik demenzieller Erkrankungen gemäß der gängigen Empfehlungen für die Praxis. Sehr uneinheitlich stellt sich dagegen die Situation hinsichtlich Umfang und Qualität therapeutischer sowie beratender und betreuender Angebote dar. Als Hauptschwierigkeiten von GS lassen sich unzureichende Finanzierung bzw. Rückvergütung von sowohl medizinischen als vor allem auch nicht-medizinischen Leistungen, Spät-Diagnosen sowie die mangelhafte Kooperation mit niedergelassenen Ärzten ermitteln. Zur Verbesserung der Versorgungsstruktur demenziell erkrankter Menschen und ihrer Angehörigen ist die Etablierung eines weitgehend einheitlichen abrechnungsfähigen Standards bei der Erkennung und Behandlung demenzieller Erkrankungen unter Berücksichtigung der Zweckorientierung der bestehenden Einrichtungen dringend nötig.
Neuropsychologische Störungen bei einem monozygoten Zwillingspaar mit Chorea-Akanthozytose
Authors: Möbes Janine , Buddensiek Nadine , Dengler Reinhard , Emrich Hinderk M. , Peschel Thomas , Müller-Vahl Kirsten
Published: September 2006

Zusammenfassung: Chorea-Akanthozytose (ChAc) ist eine seltene, genetisch bedingte Erkrankung, welche durch charakteristische neurologische und psychiatrische Symptome gekennzeichnet ist. In der vorliegenden Fallbeschreibung wird ein männliches monozygotes Zwillingspaar vorgestellt, das aufgrund ähnlicher Kombinationen komplexer Bewegungsstörungen (choreatische und parkinsonähnliche Bewegungen), Dystonien und Vokalisationen sowie Verhaltensauffälligkeiten und kognitive Beeinträchtigungen als Tourette-Syndrom fehldiagnostiziert wurde. Eine ausführliche neuropsychologische Untersuchung deutete auf eine fronto-subkortikale Demenz, wobei einige Befunde zwischen den Brüdern diskrepant waren. Die unterschiedlichen Ergebnisse der neurologischen, neuropsychologischen und psychiatrischen Untersuchung lassen annehmen, dass neben genetischen auch nicht-genetische Faktoren die klinische Symptomatik der ChAc Patienten beeinflussen. Darüber hinaus verdeutlicht der Fallbericht, dass eine detaillierte neuropsychologische Untersuchung einen wesentlichen Beitrag zur Diagnosesicherung der ChAc leisten kann.
Störungen des Gedächtnisses bei Schizophrenie: Falldarstellung
Authors: Albert Anita , Kunz Miriam , Lautenbacher Stefan
Published: September 2006

Zusammenfassung: Vorgestellt wird der Fall eines jungen Mannes mit langjähriger paranoider Schizophrenie, die mit einer eingeschränkten kognitiven Leistungsfähigkeit und einer episodenhaft ausgeprägten Negativsymptomatik einhergeht. Neuropsychologisch imponiert eine starke Einschränkung des verbalen Neugedächtnisses und vermutlich auch des Sequenzlernens vor dem Hintergrund von milden Störungen exekutiver Funktionen, der Aufmerksamkeit und sonstiger Gedächtnisleistungen. Dieses für schizophrene Patienten typische Bild einer besonderen Betroffenheit von Gedächtnisleistungen wird im Zusammenhang mit seiner Bedeutung für die Vorhersage der beruflichen und sozialen Rehabilitation diskutiert.
Emotionen und Gedächtnis bei Patienten mit Alzheimer-Demenz
Authors: Blessing Andreas , Martin Mike , Wenz Michael , Zöllig Jacqueline
Published: September 2006

Zusammenfassung: Dieser Übersichtsartikel hat das Ziel, Zusammenhänge von Emotionen und Gedächtnisleistungen bei Alzheimerpatienten aufzuzeigen und dabei auf Ressourcen der Patienten in diesem Bereich einzugehen. Neurophysiologische Veränderungen durch die Alzheimerdemenz werden kurz diskutiert und mit neuroanatomischen Strukturen, die an der Verarbeitung von Emotionen beteiligt sind, in Verbindung gebracht. Auf dieser Grundlage wird ein Überblick über Studien mit Alzheimerpatienten gegeben, die (a) den emotionalen Gedächtniseffekt erforschen, oder (b) Emotionen als Gedächtnisinhalte bei Alzheimerpatienten untersuchen. Abschließend werden offene Forschungsfragen mit Blick auf Konsequenzen dieser Befunde für die nichtmedikamentöse Therapie diskutiert.
Frühe Läsionen und die Plastizität des menschlichen Gehirns
Authors: Lidzba Karen
Published: September 2006

Zusammenfassung: Während der Entwicklung des Gehirns ist eine flexible Reaktion auf negative Einflüsse u. a. dank einer anfänglichen “Überproduktion” neuronaler Substanz möglich. Frühe, umschriebene und unilaterale Läsionen haben weniger negative Auswirkungen auf die kognitive und motorische Entwicklung, als diffuse, bilaterale oder später in der Kindheit erworbene Schädigungen. Viele Kinder mit frühen Läsionen leiden an einer Cerebralparese, die meist milder ausfällt als bei Erwachsenen mit vergleichbaren Läsionen. Sprachliche Defizite, wie Aphasien, werden bei Kindern mit frühen Läsionen selten beobachtet, was durch eine Reorganisation der Sprachfunktion in die ungeschädigte rechte Hemisphäre erklärt wird. Je stärker die rechte Hemisphäre an der Sprachfunktion beteiligt ist, umso mehr zeigen die Betroffenen jedoch Defizite in räumlich-visuellen Funktionen. Dieses Beispiel zeigt die Grenzen der Kompensationsmöglichkeiten des sich entwickelnden Gehirns.
Comparison between the temperature measurements by TIMED/SABER and lidar in the midlatitude
Authors: Xu Jiyao , She C. Y. , Yuan Wei , Mertens Chris , Mlynczak Marty , Russell James
Published: September 2006

Comparisons of monthly mean nighttime temperature profiles observed by the sodium lidar at Colorado State University and TIMED/SABER overpasses are made. In the altitude range from 85 km to about 100 km, the two observations are in very good agreement. Though within each other's error bars, important differences occur below 85 km in the entire year and above 100 km in the summer season. Possible reasons for these difference are high photon noise below 85 km in lidar observations and less than accurate assumptions in the concentration of important chemical species like oxygen (and its quenching rate) in the SABER retrieval above 100 km. However, the two techniques both show the two‐level mesopause thermal structure, with the times of change from one level to the other in excellent agreement. Comparison indicates that the high‐level (winter) mesopause altitudes are also in excellent agreement between the two observations, though some difference (2–3 km) may exist in the low‐level (summer) mesopause altitudes between ground‐based and satellite‐borne data. In addition, the difference in local time dependency between lidar and SABER is investigated; this difference makes the comparison of mesopause altitudes difficult.
Nonlinear trends and multiyear cycles in sea level records
Authors: Jevrejeva S. , Grinsted A. , Moore J. C. , Holgate S.
Published: September 2006

We analyze the Permanent Service for Mean Sea Level (PSMSL) database of sea level time series using a method based on Monte Carlo Singular Spectrum Analysis (MC‐SSA). We remove 2–30 year quasi‐periodic oscillations and determine the nonlinear long‐term trends for 12 large ocean regions. Our global sea level trend estimate of 2.4 ± 1.0 mm/yr for the period from 1993 to 2000 is comparable with the 2.6 ± 0.7 mm/yr sea level rise calculated from TOPEX/Poseidon altimeter measurements. However, we show that over the last 100 years the rate of 2.5 ± 1.0 mm/yr occurred between 1920 and 1945, is likely to be as large as the 1990s, and resulted in a mean sea level rise of 48 mm. We evaluate errors in sea level using two independent approaches, the robust bi‐weight mean and variance, and a novel “virtual station” approach that utilizes geographic locations of stations. Results suggest that a region cannot be adequately represented by a simple mean curve with standard error, assuming all stations are independent, as multiyear cycles within regions are very significant. Additionally, much of the between‐region mismatch errors are due to multiyear cycles in the global sea level that limit the ability of simple means to capture sea level accurately. We demonstrate that variability in sea level records over periods 2–30 years has increased during the past 50 years in most ocean basins.
A multimodel ensemble forecast framework: Application to spring seasonal flows in the Gunnison River Basin
Authors: Regonda Satish Kumar , Rajagopalan Balaji , Clark Martyn , Zagona Edith
Published: September 2006

We propose a multimodel ensemble forecast framework for streamflow forecasts at multiple locations that incorporates large‐scale climate information. It has four broad steps: (1) Principal component analysis is performed on the spatial streamflows to identify the dominant modes of variability. (2) Potential predictors of the dominant streamflow modes are identified from several large‐scale climate features and snow water equivalent information. (3) Objective criterion is used to select a suite of candidate nonlinear regression models each with different predictors. (4) Ensemble forecasts of the dominant streamflow modes are generated from the candidate models and are combined objectively to produce a multimodel ensemble, which are then back transformed to produce spatially coherent streamflow forecasts at all the locations. The utility of the framework is demonstrated in the skillful forecast of spring seasonal streamflows at six locations in the Gunnison River Basin at several lead times. The generated ensemble streamflow forecast provides valuable and useful information for optimal management and planning of water resources in the basin.
Role of dust devils and orbital precession in closing the Martian dust cycle
Authors: Haberle R. M. , Kahre M. A. , Murphy J. R. , Christensen P. R. , Greeley R.
Published: September 2006

We use a general circulation model to simulate the role of dust devils on the Martian dust cycle as a function of orbital precession. We focus specifically on the two most recent epochs of 22,500 and 72,500 years ago when perihelion occurred near northern summer solstice. We find that dust devils dominate the dust cycle at these times and that while orbital precession does modulate the exchange of dust between the hemispheres, the integrated effect is a net transfer of dust from north to south. The low thermal inertia continents of Tharsis, Arabia, and Elysium are the main regions that contribute to the net loss in the Northern Hemisphere and this loss is primarily due to dust devils. These results suggests that the dust cycle is closed on time scales longer than those associated with orbital precession (∼50,000 years) and that obliquity variations must also play an important role in the long‐term dust cycle.
Effect of shallow cumulus convection on the eastern Pacific climate in a coupled model
Authors: de Szoeke Simon P. , Wang Yuqing , Xie Shang‐Ping , Miyama Toru
Published: September 2006

Shallow cumulus convection evaporates stratocumulus clouds in the atmospheric boundary layer. The effect of shallow convection on the large‐scale climate of the eastern tropical Pacific is investigated with a coupled ocean‐atmosphere model by disabling the shallow convection parameterization (noSC). Without shallow convection, the stratiform cloud fraction increases and surface solar radiation decreases. The sea surface temperature (SST) cools on average by 2°C. The cooling in noSC is larger under the low cloud deck south of the equator than north of the equator, resulting in an increase in the climatic meridional asymmetry. In the control run an ITCZ forms south of the equator in March‐April. In noSC the SST is at most 24°C south of the equator and an ITCZ does not form. The perennial northern‐hemisphere ITCZ in noSC is accompanied by year‐round southerlies of at least ∼3 m s−1 on the equator, considerably reducing the seasonal cycle of equatorial SST.
Secondary organic aerosol formation from anthropogenic air pollution: Rapid and higher than expected
Authors: Volkamer Rainer , Jimenez Jose L. , San Martini Federico , Dzepina Katja , Zhang Qi , Salcedo Dara , Molina Luisa T. , Worsnop Douglas R. , Molina Mario J.
Published: September 2006

The atmospheric chemistry of volatile organic compounds (VOCs) in urban areas results in the formation of ‘photochemical smog’, including secondary organic aerosol (SOA). State‐of‐the‐art SOA models parameterize the results of simulation chamber experiments that bracket the conditions found in the polluted urban atmosphere. Here we show that in the real urban atmosphere reactive anthropogenic VOCs (AVOCs) produce much larger amounts of SOA than these models predict, even shortly after sunrise. Contrary to current belief, a significant fraction of the excess SOA is formed from first‐generation AVOC oxidation products. Global models deem AVOCs a very minor contributor to SOA compared to biogenic VOCs (BVOCs). If our results are extrapolated to other urban areas, AVOCs could be responsible for additional 3–25 Tg yr−1 SOA production globally, and cause up to −0.1 W m−2 additional top‐of‐the‐atmosphere radiative cooling.
Cellular effects and metabolic stability of N1‐cyclic inosine diphosphoribose and its derivatives
Authors: Kirchberger T , Wagner G , Xu J , Cordiglieri C , Wang P , Gasser A , Fliegert R , Bruhn S , Flügel A , Lund F E , Zhang L‐h , Potter B V L , Guse A H
Published: September 2006

Background and purpose:

Recently, a number of mimics of the second messenger cyclic ADP‐ribose (cADPR) with replacement of adenosine by inosine were introduced. In addition, various alterations in the molecule ranging from substitutions at C8 of the base up to full replacement of the ribose moieties still retained biological activity. However, nothing is known about the metabolic stability and cellular effects of these novel analogues.

Experimental approach:

cADPR and the inosine‐based analogues were incubated with CD38, ADP‐ribosyl cyclase and NAD‐glycohydrolase and metabolism was analysed by RP‐HPLC. Furthermore, the effect of the analogues on cytokine expression and proliferation was investigated in primary T‐lymphocytes and T‐lymphoma cells.

Key results:

Incubation of cADPR with CD38 resulted in degradation to adenosine diphosphoribose. ADP‐ribosyl cyclase weakly catabolised cADPR whereas NAD‐glycohydrolase showed no such activity. In contrast, N1‐cyclic inosine 5′‐diphosphoribose (N1‐cIDPR) was not hydrolyzed by CD38. Three additional N1‐cIDPR analogues showed a similar stability. Proliferation of Jurkat T‐lymphoma cells was inhibited by N1‐cIDPR, N1‐[(phosphoryl‐O‐ethoxy)‐methyl]‐N9‐[(phosphoryl‐O‐ethoxy)‐methyl]‐hypoxanthine‐cyclic pyrophosphate (N1‐cIDP‐DE) and N1‐ethoxymethyl‐cIDPR (N1‐cIDPRE). In contrast, in primary T cells neither proliferation nor cytokine expression was affected by these compounds.

Conclusions and Implications:

The metabolic stability of N1‐cIDPR and its analogues provides an advantage for the development of novel pharmaceutical compounds interfering with cADPR mediated Ca2+ signalling pathways. The differential effects of N1‐cIDPR and N1‐cIDPRE on proliferation and cytokine expression in primary T cells versus T‐lymphoma cells may constitute a starting point for novel anti‐tumor drugs.

British Journal of Pharmacology (2006) 149, 337–344. doi:10.1038/sj.bjp.0706869
Combined hERG channel inhibition and disruption of trafficking in drug‐induced long QT syndrome by fluoxetine: a case‐study in cardiac safety pharmacology
Authors: Hancox J C , Mitcheson J S
Published: September 2006

Drug‐induced prolongation of the rate‐corrected QT interval (QTCI) on the electrocardiogram occurs as an unwanted effect of diverse clinical and investigational drugs and carries a risk of potentially fatal cardiac arrhythmias. hERG (human ether‐à‐go‐go‐related gene) is the gene encoding the α‐subunit of channels mediating the rapid delayed rectifier K+ current, which plays a vital role in repolarising the ventricles of the heart. Most QTCI prolonging drugs can inhibit the function of recombinant hERG K+ channels, consequently in vitro hERG assays are used widely as front‐line screens in cardiac safety‐testing of novel chemical entities. In this issue, Rajamani and colleagues report a case of QTCI prolongation with the antidepressant fluoxetine and correlate this with a dual effect of the drug and of its major metabolite norfluoxetine on hERG channels. Both compounds were found to produce an acute inhibition of the hERG channel by pharmacological blockade, but in addition they also were able to disrupt the normal trafficking of hERG protein to the cell membrane. Mutations to a key component of the drug binding site in the S6 region of the channel greatly attenuated channel block, but did not impair disruption of trafficking; this suggests that channel block and drug effects on trafficking were mediated by different mechanisms. These findings add to growing evidence for disruption of hERG channel trafficking as a mechanism for drug‐induced long QT syndrome and raise questions as to possible limitations of acute screening methods in the assessment of QTcI prolonging liability of drugs in development.

British Journal of Pharmacology (2006) 149, 457–459. doi:10.1038/sj.bjp.0706890
Drug‐induced long QT syndrome: hERG K+channel block and disruption of protein trafficking by fluoxetine and norfluoxetine
Authors: Rajamani S , Eckhardt L L , Valdivia C R , Klemens C A , Gillman B M , Anderson C L , Holzem K M , Delisle B P , Anson B D , Makielski J C , January C T
Published: September 2006

Background and purpose:

Fluoxetine (Prozac®) is a widely prescribed drug in adults and children, and it has an active metabolite, norfluoxetine, with a prolonged elimination time. Although uncommon, Prozac causes QT interval prolongation and arrhythmias; a patient who took an overdose of Prozac exhibited a prolonged QT interval (QTc 625 msec). We looked for possible mechanisms underlying this clinical finding by analysing the effects of fluoxetine and norfluoxetine on ion channelsin vitro.

Experimental approach:

We studied the effects of fluoxetine and norfluoxetine on the electrophysiology and cellular trafficking of hERG K+and SCN5A Na+channels heterologously expressed in HEK293 cells.

Key results:

Voltage clamp analyses employing square pulse or ventricular action potential waveform protocols showed that fluoxetine and norfluoxetine caused direct, concentration‐dependent, block of hERG current (IhERG). Biochemical studies showed that both compounds also caused concentration‐dependent reductions in the trafficking of hERG channel protein into the cell surface membrane. Fluoxetine had no effect on SCN5A channel or HEK293 cell endogenous current. Mutations in the hERG channel drug binding domain reduced fluoxetine block of IhERGbut did not alter fluoxetine's effect on hERG channel protein trafficking.

Conclusions and implications:

Our findings show that both fluoxetine and norfluoxetine at similar concentrations selectively reduce IhERGby two mechanisms, (1) direct channel block, and (2) indirectly by disrupting channel protein trafficking. These two effects are not mediated by a single drug binding site. Our findings add complexity to understanding the mechanisms that cause drug‐induced long QT syndrome.

British Journal of Pharmacology(2006)149, 481–489. doi:10.1038/sj.bjp.0706892
Ab initio correlation functionals from second-order perturbation theory
Authors: Schweigert Igor V. , Lotrich Victor F. , Bartlett Rodney J.
Published: September 2006

Orbital-dependent exchange-correlation functionals are not limited by the explicit dependence on the density and present an attractive alternative to conventional functionals. With the successful implementation of the exact orbital-dependent exchange functional, the challenge lies in developing orbital-dependent approximations for the correlation functional. Ab initio many-body methods can provide such approximations. In particular, perturbation theory with the Kohn-Sham model as the reference [Görling and Levy, Phys. Rev. A 50, 196 (1994)] defines the exact correlation functional via an infinite perturbation series. The second-order term of these series gives the lowest-order approximation to the correlation functional. However, it has been suggested [Bartlett et al., J. Chem. Phys. 122, 034104 (2005)] that the Kohn-Sham Hamiltonian is not the optimal choice for the perturbation expansion and a different reference Hamiltonian may lead to an improved perturbation series and more accurate second-order approximation. Here, we demonstrate explicitly that the modified series can be used to define superior functional and potential. We present results of atomic and molecular calculations with both second-order functionals. Our results demonstrate that the modified functional offers a significantly improved description of the correlation effects as it does not suffer from convergence problems and results in energies and densities that are more accurate than those obtained with second-order Møller-Plesset perturbation theory or generalized-gradient approximation functionals.
A Monte Carlo approach of remanence enhancement in Potts spin lattice
Authors: Zuo H. B. , Zhang M. F. , Liu J.-M.
Published: September 2006

The hysteresis dynamics of a multidomain Potts lattice with nonzero domain wall width is simulated using kinetic Monte Carlo method. The remanence enhancement effect is investigated in detail taking into account full spin relaxation in the domain walls, whereas outside domain walls only spin reverse event is allowed. Significant enhancement of the remanence and weakening of the coercivity with increasing domain walls is revealed. While the dependence of the remanence and coercivity on domain size and domain wall width is established, the hysteresis area is found to be conserved against the two variables. The conservation property of the hysteresis area predicts that no excess energy is required for the spin relaxation inside the domain walls, thus the remanence enhancement. Finally, the theoretically predicted scaling relation on the remanence enhancement is confirmed with the present simulation.
Stability of magnetic configurations in nanorings
Authors: Landeros P. , Escrig J. , Altbir D. , Bahiana M. , d’Albuquerque e Castro J.
Published: September 2006

The relative stability of the vortex, onion, and ferromagnetic phases in nanorings is examined as a function of the ring geometry. Total energy calculations are carried out analytically, based on simple models for each configuration. Results are summarized by phase diagrams, which might be used as a guide to the production of rings with specific magnetic properties.
Growth modes of carbon nanotubes on metal substrates
Authors: Matthews Kristopher D. , Lemaitre Maxime G. , Kim Taekyung , Chen Hao , Shim Moonsub , Zuo Jian-Min
Published: September 2006

Growth temperature induced changes in Al∕Fe thin film catalysts are examined for chemical vapor deposition of carbon nanotubes directly on metal substrates. The film thickness, growth temperature, and supporting substrate affect the size and the density of Fe catalyst nanoparticles which in turn control the diameter, length, and single versus multiwalled nature of carbon nanotubes. Growths on two metal substrates, Au and Mo, using sputter deposited Al∕Fe thin films are compared by transmission and scanning electron microscopy, and Raman analyses. Striking differences in the growth modes are observed with Au substrate enhancing multiwalled nanotube growth with metal catalyst particles at the tip away from the substrate and Mo substrate promoting single-walled nanotube growth with the catalyst nanoparticles remaining on the substrate. Oxidative treatment of Mo underlayer (i.e., relatively thick layer Mo sputtered on Au prior to Al∕Fe catalyst deposition) can also induce nanotube growth with catalyst particles at the tips but with single-walled structure. These results suggest the importance of the support catalyst (Al∕AlxOy) adhesion strength on substrates in determining nanotube growth modes.
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turbulence model for the self-similar growth of the Rayleigh-Taylor and Richtmyer-Meshkov instabilities
Authors: Dimonte Guy , Tipton Robert
Published: September 2006

A turbulence model is developed to described the self-similar growth of the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities. The model describes the dominant eddies in the mixing zone with evolutionary equations for their characteristic dimension L and energy per unit mass K≡V2∕2. The equations are based on the successful buoyancy-drag models for RT and RM flows, but constructed only with local parameters so that it can be applied to multidimensional flows with multiple shells of materials. The model has several unknown coefficients that are determined by comparing analytical and numerical solutions with RT and RM experiments.
Quantitative analysis of hydrogenated diamondlike carbon films by visible Raman spectroscopy
Authors: Singha Achintya , Ghosh Aditi , Roy Anushree , Ray Nihar Ranjan
Published: September 2006

The correlations between properties of hydrogenated diamondlike carbon films and their Raman spectra have been investigated. The films are prepared by plasma deposition technique, keeping different hydrogen to methane ratios during the growth process. The hydrogen concentration, sp3 content, hardness, and optical Tauc gap of the materials have been estimated from a detailed analysis of their Raman spectra. We have also measured the same parameters of the films by using other commonly used techniques, such as sp3 content in films by x-ray photoelectron spectroscopy, their Tauc gap by ellipsometric measurements, and hardness by microhardness testing. The reasons for the mismatch between the characteristics of the films, as obtained by Raman measurements and by the above mentioned techniques, have been discussed. We emphasize on the importance of the visible Raman spectroscopy in reliably predicting the above key properties of diamondlike carbon films.
Coupled optoelectronic modeling and simulation of nanowire lasers
Authors: Chen L. , Towe E.
Published: September 2006

A self-consistent, coupled optoelectronic simulation approach for studying microcavity nanowire lasers is presented. To focus the discussion, we use GaN nanowires to illustrate the methodology. The comprehensive model solves, simultaneously and self-consistently, the carrier transport equations and the photon rate equations. The basic physical model takes into account both bulk and surface dark carrier recombination processes. It includes stimulated emission, the anisotropic optical gain typical of the wurtzite GaN structure, the modified spontaneous emission, and its coupling into the lasing modes as a consequence of microcavity effects. The model further incorporates band-gap shrinkage effects due to band renormalization; it includes the complex dispersion and reflectivity relations of the guided modes, and the effects of multiple lateral and longitudinal lasing and nonlasing optical modes. We provide a detailed discussion of the influence of other important effects on the operation of optically pumped GaN nanowire lasers. Finally, we want to point out that the method is sufficiently general that it can be used to study any class of nanowire lasers.
Screen printed thick self-biased, low-loss, barium hexaferrite films by hot-press sintering
Authors: Chen Yajie , Sakai Tomokazu , Chen Taiyang , Yoon Soack D. , Vittoria Carmine , Harris Vincent G.
Published: September 2006

Ba Fe 12 O 19 hexaferrite thick films having high hysteresis loop squareness (Mr∕Ms) and low ferromagnetic resonance (FMR) linewidths were processed through the use of a screen printing technique coupled with hot-press sintering. Scanning electron microscopy and x-ray diffraction measurements exhibit strong crystallographic c-axis alignment of crystals perpendicular to the film plane. Static magnetic resonance and FMR measurements were performed to determine the effect of the preparation technique on magnetic hysteresis and microwave properties. Hot pressing during sintering produced dense thick films having high squareness (>0.95) and reduced coercivity (∼1900Oe). Of greater importance was the measurement of a minimum peak-to-peak FMR linewidth, 320Oe at the U band, for films ranging in thickness from 100to500μm. Theoretic estimates suggest that such narrow linewidths can be attributed to the reduction in porosity and the improvement in c-axis orientation of crystallites in polycrystalline barium ferrite films. As such, haxaferrite materials prepared using this technique offer opportunities in the next generation of self-biased planar microwave devices.
Constructal theory of generation of configuration in nature and engineering
Authors: Bejan Adrian , Lorente Sylvie
Published: September 2006

Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997); Int. J. Heat Mass Transfer, 40, 799 (1997)]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.
Reactive pulsed laser deposition of hydrogenated carbon thin films: The effect of hydrogen pressure
Authors: Budai J. , Tóth Z. , Juhász A. , Szakács G. , Szilágyi E. , Veres M. , Koós M.
Published: September 2006

Diamondlike properties of amorphous carbon films can be enhanced by applying reactive hydrogen atmosphere during pulsed laser deposition (PLD) as shown by recent studies. The complex phenomena occurring during carbon plume expansion has not been examined yet thoroughly. Therefore we deposited amorphous hydrogenated carbon thin films in hydrogen ambient atmosphere (4×10−4–25Pa) by PLD at room temperature. The deposited films were characterized by Rutherford backscattering spectrometry, elastic recoil detection analysis, Raman spectroscopy, infrared spectroscopy, variable angle spectroscopic ellipsometry, and nanoindentation measurements. At low hydrogen pressures (below ∼0.1Pa), when the mean free path of plasma constituents in the background gas is larger than the target substrate distance, the deposited films show diamondlike properties. At higher pressures (above ∼0.1Pa) the deposited films change their diamondlike carbon character towards to a structure which contains increasing amount of sp2 bonded carbon sites. Further increase in pressure (above ∼2Pa) results in hydrogenated carbon films with increasing hydrogen content. Principally these changes are caused by the energy decrease of the plume when plasma is decelerated by the background gas. Chemical reactions also effect the composition of the films especially in the highest pressure domain.
Influence of deposition temperature, solvent, and solute concentration on the deposition mechanisms and final structure of mercury iodide fabricated using the spray pyrolysis technique
Authors: Ugucioni J. C. , Mulato M.
Published: September 2006

Mercury iodide (HgI2) samples were deposited by spray pyrolysis under varying fabrication parameters. Different solvents (water and ethanol) and substrate temperatures (from 40 up to 130°C) were used. Yellowish films were obtained using water and temperatures above 100°C, while reddish films were obtained using ethanol and temperatures below 75°C. The structure and the stoichiometry of the samples were investigated using x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The yellowish films show lattice constants of 4.379, 7.1953, and 12.5505Å that correspond to a space group similar to the structure of the orthorhombic β-HgI2. The reddish films show lattice constant averages of 4.3550 and 12.2200Å that correspond to a space group similar to the structure of the tetragonal α-HgI2. We observed problems related to the stoichiometry of the films caused by the volatile characteristic of iodine atoms. Typical thickness can be estimated to be around a few microns. The deposition mechanisms and final structure of the samples are discussed as a function of deposition temperature, type of solvent, and solute concentration. Optimized deposition conditions are presented for the development of thin films for radiation detectors.
Argon plasma exposure enhanced intermixing in an undoped InGaAsP∕InP quantum-well structure
Authors: Nie D. , Mei T. , Tang X. H. , Chin M. K. , Djie H. S. , Wang Y. X.
Published: September 2006

Intermixing in an undoped InGaAsP∕InP quantum well structure enhanced by near-surface defects generated using inductively coupled argon plasma is temperature dependent. The group III sublattice interdiffusion can be four times as fast as that of the group V sublattice for the annealing temperature lower than 600°C, and a maximum band gap redshift of 50nm is obtained in experiment. Blueshift is obtained at 700°C when the group V sublattice interdiffusion becomes appreciable.
Magnetic domain structure and dynamics in interacting ferromagnetic stacks with perpendicular anisotropy
Authors: Wiebel S. , Jamet J.-P. , Vernier N. , Mougin A. , Ferré J. , Baltz V. , Rodmacq B. , Dieny B.
Published: September 2006

The time and field dependence of the magnetic domain structure at magnetization reversal were investigated by Kerr microscopy in a structure consisting of a hard and a soft ferromagnetic Co∕Pt multilayer stack with perpendicular anisotropy, separated by a thicker nonmagnetic Pt spacer layer. Large local inhomogeneous magnetostatic stray fields appear as soon as a nonuniform magnetic area exists within one of the stacks and induce a correlated domain structure within the other. The long range nature of this magnetostatic interaction gives rise to ultraslow dynamics even in zero applied field, i.e., it affects the long time domain stability. Due to this additional interaction field, the magnetization reversal under short magnetic field pulses differs markedly from the well-known slow dynamic behavior. Namely, in high field, the magnetization of the coupled harder layer has been observed to reverse more rapidly by domain wall motion than the softer layer alone.
Rabi oscillations in a strongly driven semiconductor quantum well
Authors: Paspalakis Emmanuel , Tsaousidou Margarita , Terzis Andreas F.
Published: September 2006

We study the interaction of an ac electric field with a semiconductor quantum well by using the effective nonlinear Bloch equations. Only the first two electron subbands in the well are considered. We apply the rotating wave approximation and derive analytical solutions for the Bloch equations for two different values of the detuning. At exact resonance we find a critical value of the Rabi frequency around which the dynamics of the system changes abruptly. Above this critical value one obtains electron oscillations with complete inversion in the two-subband system, while below this value we obtain electron oscillations without complete inversion and with the majority of the electron population on average in the lower subband. We also present numerical calculations for a specific quantum well structure and assess the limits of validity of the analytical results.
Vortex pinning in Nb thin films modulated by nanospheres
Authors: Vinckx Wim , Vanacken Johan , Moshchalkov Victor V.
Published: September 2006

Superconducting Nb thin films deposited on top of self-assembled spherical nanoparticles have been investigated by transport measurements. Colloid polystyrene nanospheres have been organized by convective self-assembly into colloid crystals. These crystals serve as modulation templates for the Nb thin films which are deposited on top. These periodic arrays provide a natural topographic pattern to modulate laterally the superconducting order parameter in deposited Nb films. The nanoparticle diameter effectively controls the matching fields and flux pinning properties of these films. The superconducting phase boundary and matching effects have been studied for Nb films grown on the templates formed by polystyrene particles with diameter d=202 and d=357nm. The triangular colloid lattice geometry induces strong modulation in thin Nb layers. In combination with the short range crystalline order of the templates, this leads to geometrical vortex ordering effects and vortex density dependent matching phenomena.
Structure of latent tracks in rutile single crystal of titanium dioxide induced by swift heavy ions
Authors: Awazu Koichi , Wang Xiaomin , Fujimaki Makoto , Komatsubara Tetsuo , Ikeda Takahiro , Ohki Yoshimichi
Published: September 2006

The structurally damaged zone in titanium dioxide rutile single crystal induced by MeV-order heavy ions was observed using high resolution electronic microscopy (HREM). Stressed regions as well as amorphous regions were identified in the damaged areas. Both stressed and amorphous regions were etched with hydrofluoric acid. The thermal spike model was used to calculate the track radii variation versus electron stopping power. When the calculated lattice temperature did not exceed the melting point of rutile titanium dioxide (2130K), no structural change introduced by ions, such as 90MeV Cl, was observed by HREM. It was found that the radius of the lattice temperature over the melting point corresponded closely to the radius of the stressed region. It was concluded that both stressed and amorphous regions are the result of quenching by molten titanium dioxide.
Evidence for electrical spin tunnel injection into silicon
Authors: Dennis C. L. , Gregg J. F. , Ensell G. J. , Thompson S. M.
Published: September 2006

Electrical spin injection into silicon was studied in a ferromagnet∕insulator∕silicon∕insulator∕ferromagnet structure, where the insulator is Si3N4. Si3N4 barriers conduct by hopping conduction at low voltages, but switch to Fowler-Nordheim tunneling at high voltages. In the Fowler-Nordheim tunneling regime a magnetic field dependence of the output current consistent with spin dependent transport through the silicon is observed; in the hopping conduction regime reduced magnetic field dependence of the output current is observed. This voltage dependence of the magnetic sensitivity strongly supports the existence of spin injection into silicon. After correction for Lorentz magnetoresistance, the magnitude of this signal is 4.1%±0.5% (12%±5%) for p-type (n-type) Si.
Spin relaxation in a germanium nanowire
Authors: Patibandla S. , Pramanik S. , Bandyopadhyay S. , Tepper G. C.
Published: September 2006

We report experimental study of spin transport in nanowire spin valve structures consisting of three layers—cobalt, germanium, and nickel. The spin diffusion length in the Ge is estimated to be about 400nm at 1.9K and the corresponding spin relaxation time is about 4ns. At 100K, the spin diffusion length drops to 180nm and the relaxation time is about 0.81ns. These short relaxation times, which depend weakly on temperature, are caused by strong surface roughness scattering that causes rapid spin relaxation via the Elliott-Yafet mode [Elliott, Phys. Rev. 96, 266 (1954)].
Detection of ferromagnetic particles using spin valve sensors
Authors: Lui L. W. Y. , Tan Y. Y. , Li K. B. , Sow C. H. , O’Shea S. J.
Published: September 2006

We have attached single ferromagnetic particles of 8μm diameter to the tips of microfabricated atomic force microscope cantilevers. These cantilevers were magnetized to fix the magnetization direction of the ferromagnetic particles and scanned in a controlled manner over a spin valve structure of dimension 12×8μm2. Two dimensional image scans representing the change in resistance of the spin valve due to a scanning bead were obtained. The results are explained using a simple model where the scanning bead is treated as a pure dipole.
Magnetism of (Dy0.5Er0.5)Al2 single crystal in ac and dc magnetic fields
Authors: Levin E. M. , Gschneidner K. A. , Lograsso T. , Schlagel D. L.
Published: September 2006

The temperature (4.2–90K), ac magnetic field (1.25–50Oe), frequency (5–125Hz), and bias dc magnetic field (0–10kOe) dependencies of the real and imaginary components of the ac magnetic susceptibility, and the temperature (4.2–250K) and dc magnetic field (0.1–50kOe) dependencies of the dc magnetic susceptibility and magnetization of a (Dy0.5Er0.5)Al2 single crystal have been studied. Isothermal magnetization measurement in a dc magnetic field indicates that (Dy0.5Er0.5)Al2 orders ferromagnetically at 37K. The ac and dc magnetic susceptibilities of (Dy0.5Er0.5)Al2 exhibit a similar behavior in the paramagnetic region but quite different behaviors in the ferromagnetic state. Both the real and imaginary components of the ac magnetic susceptibility are sensitive to the applied ac magnetic field, the crystallographic direction, and the bias magnetic field, showing that domain wall dynamics mainly account for the response to the ac magnetic field. The contributions to the magnetization process arise from the magnetically ordered Dy and Er sublattices and depend upon the single-ion anisotropy of the Dy and Er ions.
Field dependent negative capacitance in small-molecule organic light-emitting diodes
Authors: Pingree L. S. C. , Russell M. T. , Marks T. J. , Hersam M. C.
Published: September 2006

Frequency dependent charge transport in organic light-emitting diodes, including marked negative capacitance (NC), is reproduced through an equivalent circuit model. The robustness of the model is tested through impedance spectroscopy characterization as a function of bias changes and layer thickness modifications. Correlations with current-voltage measurements reveal that the NC occurs once trap assisted space charge limited transport is reached. Through variation of the organic layer thicknesses, the magnitude of the NC response can be precisely tuned. In particular, increasing the thickness of the electron transport layer increases the NC magnitude, whereas hole transport layer thickness modifications have little effect on the magnitude of NC. Subsequent modeling indicates that alterations in the distribution of the electric field across the individual organic layers account for the observed variations in NC. In addition, it is found that the time constants for the inductive elements of the model increase with applied bias, unlike their capacitive counterparts, suggesting that an accumulation of charge at the organic/organic interface is responsible for both the increasing NC and redistribution of the applied field.
Periodic lines and holes produced in thin Au films by pulsed laser irradiation
Authors: Kaganovskii Yu. , Vladomirsky H. , Rosenbluh M.
Published: September 2006

A technique for the fabrication of periodic lines and holes in thin gold films (5–50nm thick) on a glass substrate by irradiation with two and four intersecting beams of a nanosecond pulsed laser is demonstrated. The two- or four-beam interference creates a one-dimensional or two-dimensional periodically alternating intensity distribution, respectively. It is shown that the threshold intensity necessary for the fabrication of periodic structures is not a monotonous function of increasing film thickness and also depends on the period of the structure. In films thicker than 17nm a unique redistribution of the film material was observed at the high intensity lines or spots. At these “hot” locations we observed the formation of tall and narrow ridges and rims caused by the hydrodynamic flow of the molten metallic film in the optically induced temperature gradient, with subsequent crystallization in the “cold” regions. A model was developed which allows us to calculate the temperature distribution around irradiated regions of the film as a function of time and position for various film thicknesses, periodicities, and beam intensities, taking into account the film reflectivity and the beam intensity profile. From the temperature distribution we calculate the expected film morphology subsequent to laser irradiation and find good agreement with the measured distances between the ridges and the rim diameters.
Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals
Authors: Brien Valérie , Dauscher Anne , Machizaud Francis
Published: September 2006

The optical reflectivity of Al-based and Ti-based quasicrystalline and approximant samples were investigated versus the quality of their structural morphology using optical reflectometry, x-ray diffraction, and transmission electron microscopy. The different structural morphologies were obtained using three different preparation processes: sintering, pulsed laser deposition, and reactive cathodic magnetron sputtering. The work demonstrates that the canonical behavior of icosahedral state in specular reflectivity is extremely sensitive to different and very fine aspects of the microstructure: sizes of grains smaller than 50nm, slight local diffuse disorder, and shifts away from the icosahedral crystallographic structure (approximants). The work explains why the optical properties of the same kind of quasicrystals found in literature sometimes reveal a different behavior from one author to another. The study then confirms the work of some authors and definitely shows that the canonical behavior of icosahedral state in specular reflectivity over the 30000–50000cm−1 domain is characterized by a decreasing function made of steps. It also shows that this behavior can be interpreted thanks to the cluster hierarchy of the model of Janot [Phys. Rev. B 53, 181 (1996)].
Surface morphological evolution on single crystal films by strong anisotropic drift diffusion under capillary and electromigration forces
Authors: Ogurtani Tarik Omer , Celik Aytac
Published: September 2006

The morphological evolution of voids at unpassivated surfaces and the sidewalls of single crystal metallic films is investigated via computer simulations by using a mathematical model based on fundamental postulates of irreversible thermodynamics. The effect of drift-diffusion anisotropy on the development of surface morphological scenarios is explored under the action of electromigration (EM) and capillary forces, utilizing numerous combinations of the surface texture and the direction of the applied electric field. Analytical expressions for the interconnect catastrophic failure time due to the EM-induced transgranular wedge-shaped voids, the propagation velocity of surface solitary waves, and the incubation time of the regenerative oscillatory surface waves are deduced under the severe instability regimes, by inverse normalization procedures applied to the outputs of the extensive computer simulation experiments.