bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent trends in erythropoietin‐mediated neuroprotection
Authors: McPherson Ronald J. , Juul Sandra E.
Published: September 2007

Fifteen years of evidence have established that the cytokine erythropoietin offers promise as a treatment for brain injury. In particular, neonatal brain injury may be reduced or prevented by early treatment with recombinant erythropoietin. Extreme prematurity and perinatal asphyxia are common conditions associated with poor neurodevelopmental outcomes including cerebral palsy, mental retardation, hearing or visual impairment, and attention deficit hyperactivity disorder. When high doses of erythropoietin are administered systemically, a small proportion crosses the blood–brain barrier and can protect against hypoxic–ischemic brain injury. In addition to other protective effects, erythropoietin can specifically protect dopaminergic neurons. Since reduced dopamine neurotransmission contributes to attention deficit hyperactivity disorder, this condition may be amenable to erythropoietin treatment. This review focuses on the potential application of erythropoietin as a neuroprotectant with regard to neurologic complications of extreme prematurity, including attention deficit hyperactivity disorder. Recent concerns that early erythropoietin might exacerbate the pathologic neovascularization associated with retinopathy of prematurity are addressed.
Reflections on the knowledge base for obstetric fistula
Authors: Kelly J. , Winter H.R.
Published: September 2007

This article presents the reflections of an experienced fistula surgeon and an epidemiologist on the current knowledge base for obstetric fistula. The incidence, prevention, and management of vesico‐vaginal and recto‐vaginal fistula are discussed. The authors call for more randomized controlled trials to determine the effectiveness of surgical interventions for fistula repair.
Antinociceptive effects of tramadol and acepromazine in cats
Authors: Steagall Paulo V.M. , Taylor Polly M. , Brondani Juliana T. , Luna Stelio P.L. , Dixon Michael J.
Published: September 2007

Effects of tramadol and acepromazine on pressure and thermal thresholds were examined in eight cats. After baseline measurements, subcutaneous (SC) tramadol 1 mg/kg, acepromazine 0.1 mg/kg, tramadol 1 mg/kg with acepromazine 0.1 mg/kg, or saline 0.3 ml were given. Serial measurements were made for 24 h. Mean thermal thresholds did not change significantly [analysis of variance (ANOVA)] from baseline. The maximum thermal threshold increase above baseline was 2.8±2.8°C at 6 h ( P>0.05) after tramadol; it was above the 95% confidence interval (CI) at 0.75, 3 and 6 h. Pressure thresholds increased above baseline from 0.25 to 2 h after acepromazine ( P<0.05) and from 0.5 to 3 h after the combination ( P<0.05), with a maximum increase of 132±156 mmHg 0.25 h after acepromazine and 197±129 mmHg 0.5 h after the combination. Pressure thresholds were above the 95% CI from 0.25 to 2 h after acepromazine and from 0.5 to 3 h after the combination. SC tramadol at 1 mg/kg in cats had limited effect on thermal and pressure nociception, but this was enhanced by acepromazine. Acepromazine alone had pressure antinociceptive effects.
Bradyarrhythmia in an anaesthetised, elderly, hypertensive cat
Authors: Ticehurst Kim , Zaki Sanaa , Maddern Kieren , Lingard Amy , Barrs Vanessa , Malik Richard
Published: September 2007

A 14-year-old neutered male domestic shorthaired cat was presented to the University Veterinary Centre Sydney for evaluation and treatment of dental disease. This cat developed an unusual bradyarrhythmia under anaesthesia. The possible causes and treatment of the dysrythmia are discussed.
Antagonistic effects of atipamezole, flumazenil and 4-aminopyridine against anaesthesia with medetomidine, midazolam and ketamine combination in cats
Authors: Ueoka Naotami , Hikasa Yoshiaki
Published: September 2007

Antagonistic effects of atipamezole (ATI), flumazenil (FLU) and 4-aminopyridine (4AP) alone and in various combinations after administration of medetomidine–midazolam–ketamine (MED–MID–KET) were evaluated in cats. Animals were anaesthetised with MED (50 μg/kg), MID (0.5 mg/kg) and KET (10 mg/kg) given intramuscularly. Twenty minutes later, physiological saline, ATI (200 μg/kg), FLU (0.1 mg/kg), 4AP (0.5 mg/kg), ATI–FLU, FLU–4AP, ATI–4AP or ATI–FLU–4AP was administered intravenously. FLU, 4AP alone, or FLU–4AP did not effectively antagonise the anaesthesia, hypothermia, bradycardia, and bradypnoea induced by MED–MID–KET. ATI alone was effective. ATI–FLU, ATI–4AP and ATI–FLU–4AP combinations produced an immediate and effective recovery from anaesthesia. The combination of ATI–FLU–4AP was the most effective in antagonising the anaesthetic effects, but was associated with tachycardia, tachypnoea, excitement, and muscle tremors. Combinations with ATI are more effective for antagonising anaesthesia, but ATI–FLU–4AP is not suitable.
THE POLITICAL ECOLOGY OF THE COPAL TRADE IN THE TANZANIAN COASTAL HINTERLAND, c. 1820–1905
Authors: SUNSERI THADDEUS
Published: September 2007

Between 1830 and 1880 copal was the major trade commodity from mainland Tanzania apart from ivory. Unlike ivory, copal was a product of a distinct environment, the lowland forests of the East African coastal hinterland. This region's copal was the best in the world for making high-value carriage varnish. It therefore found a ready market in the West, especially New England, whose traders brought cotton textiles to trade with East Africans for copal. The monopolization by hinterland polities of the copal–cloth trade nexus enabled them to consolidate politically as a sub-entrepôt of the Zanzibar commercial state. After 1880 a global demand for wild rubber, a product of far more diverse landscapes, posed a threat to the copal economy, and in part ushered in German colonialism. New colonial tax, labor and conservationist policies spelled the decline of the copal economy and its communities as they lost access to the coastal forests.
THE ELEPHANT SHOOTING: COLONIAL LAW AND INDIRECT RULE IN KAOKO, NORTHWESTERN NAMIBIA, IN THE 1920s AND 1930s
Authors: RIZZO LORENA
Published: September 2007

The law as a means of sociopolitical control in colonial states has gained significance as an issue in the recent historiography of Africa. This article discusses the making of a criminal case in colonial Kaoko, northwestern Namibia in the 1920s and 30s. It focuses on the problem of African voice and narrative and the ways in which they have been transformed into written evidence in the course of legal investigation. It demonstrates that the archival documents which emerged from this case require careful methodological scrutiny if they are to be used for the reconstruction of the region's past. It goes beyond colonial law as constituting a particular discourse to conceive colonial law as a space for intervention and agency for both colonized and colonizers. The central argument raised in the article is that while the South African administration in northwestern Namibia allegedly aimed at prosecuting culprits and securing evidence for their transgressions, men and women in Kaoko used colonial law as an arena for the negotiation of social and political issues. Concerned with the case's impact on the configuration of gender, the article shows how colonial law became both a site of male representation and power, and a space for female contestation of male claims to sociopolitical mastery.
THE ENEMY WITHIN: LOYALISTS AND THE WAR AGAINST MAU MAU IN KENYA
Authors: BRANCH DANIEL
Published: September 2007

Between 1952 and 1960, the British colonial government of Kenya waged a violent counter-insurgency campaign against the Mau Mau rebels. In this effort the regime was assisted by collaborators, known as loyalists, drawn from the same communities as the insurgents. Based primarily on new archival sources, this article sets out the history of loyalism, stresses the ambiguity of allegiances during the conflict and argues that loyalism was a product of the same intellectual debates that had spawned the Mau Mau insurgency. The article concludes by stressing the significance for postcolonial Kenya of this history.
Implizites Lernen bei Patienten mit Schizophrenie
Authors: Exner Cornelia
Published: September 2007

Zusammenfassung: Patienten mit Schizophrenie weisen kognitive Leistungsminderungen insbesondere des expliziten Gedächtnisses auf. Demgegenüber wird angenommen, dass implizite Lern- und Gedächtnisleistungen unbeeinträchtigt sind. Die vorliegende Übersichtsarbeit fasst die Ergebnisse von 41 bis Dezember 2006 publizierten empirischen Studien zum impliziten Lernen bei Patienten mit Schizophrenie zusammen. In der Zusammenschau lässt sich schlussfolgern, dass schizophrenen Patienten eine große Bandbreite perzeptueller, motorischer und kognitiver Fertigkeiten durch Übung verbessern können. Die Lernraten sind trotz eines häufig reduzierten Ausgangsniveaus vergleichbar mit denen gesunder Probanden. Dagegen haben schizophrenen Patienten Schwierigkeiten, von unbekannten zugrunde liegenden Strukturen oder Regeln in den verwendeten Stimuli zu profitieren. Implizite Lernleistungen werden wenig von der Symptomschwere, wahrscheinlich aber von der Medikation beeinflusst. Die Ergebnisse werden im Kontext sonstiger kognitiver Störungen bei schizophrenen Patienten diskutiert.
Partitioning net ecosystem exchange of CO2: A comparison of a Bayesian/isotope approach to environmental regression methods
Authors: Zobitz J. M. , Burns S. P. , Ogée J. , Reichstein M. , Bowling D. R.
Published: September 2007

Separation of the net ecosystem exchange of CO2 (F) into its component fluxes of net photosynthesis (FA) and nonfoliar respiration (FR) is important in understanding the physical and environmental controls on these fluxes, and how these fluxes may respond to environmental change. In this paper, we evaluate a partitioning method based on a combination of stable isotopes of CO2 and Bayesian optimization in the context of partitioning methods based on regressions with environmental variables. We combined high‐resolution measurements of stable carbon isotopes of CO2, ecosystem fluxes, and meteorological variables with a Bayesian parameter optimization approach to estimate FA and FR in a subalpine forest in Colorado, United States, over the course of 104 days during summer 2003. Results were generally in agreement with the independent environmental regression methods of Reichstein et al. (2005a) and Yi et al. (2004). Half‐hourly posterior parameter estimates of FA and FR derived from the Bayesian/isotopic method showed a strong diurnal pattern in both, consistent with established gross photosynthesis (GEE) and total ecosystem respiration (TER) relationships. Isotope‐derived FA was functionally dependent on light, but FR exhibited the expected temperature dependence only when the prior estimates for FR were temperature‐based. Examination of the posterior correlation matrix revealed that the available data were insufficient to independently resolve all the Bayesian‐estimated parameters in our model. This could be due to a small isotopic disequilibrium () between FA and FR, poor characterization of whole‐canopy photosynthetic discrimination or the isotopic flux (isoflux, analogous to net ecosystem exchange of 13CO2). The positive sign of indicates that FA was more enriched in 13C than FR. Possible reasons for this are discussed in the context of recent literature.
Preferential settling of elongated mineral dust particles in the atmosphere
Authors: Li Jingmin , Osada Kazuo
Published: September 2007

Positions of particles' centers of gravity and folding centers were analyzed for individual dust particles in snow on a high mountain in Japan. Bias of dust particles' centers of gravity was observed: L1 (the longest distance from the center of gravity to the boundary of particles) is 5% (of L1, on average) longer than L2 (1/2 of the longest axis of particles), suggesting that a preferential orientation exists for particles settling heavy side down. Applying that preferential orientation of settling particles to Ginoux's model, the settling velocity for ellipsoids with Reynolds numbers lower than 2 was estimated. The results show that, for long‐range transport particles, settling velocity of spherical particles is lower than that of ellipsoids with equal surface area. Our results also indicate that, away from the source regions, dust particles are essentially spherical, which considerably simplify the calculation of settling velocity in transport and of radiative transfer models.
A large terrestrial source of methyl iodide
Authors: Sive Barkley C. , Varner Ruth K. , Mao Huiting , Blake Donald R. , Wingenter Oliver W. , Talbot Robert
Published: September 2007

We have identified terrestrial sources of methyl iodide (CH3I) and assessed their importance in its atmospheric budget using a synthesis of field observations. Measurements include those from NASA DC‐8 research flights over the United States and the North Atlantic, the AIRMAP long‐term ground‐observing network in New England, and a field campaign at Duke Forest, North Carolina. We found an average CH3I flux of ∼2,700 ng m−2 d−1 to the atmosphere from midlatitude vegetation and soils, a value similar in magnitude to previous estimates of the oceanic source strength. The large‐scale aircraft measurements of vertical profiles over the continental U.S. showed CH3I‐mixing ratios comparable to and greater than those observed over the North Atlantic. Overall, midlatitude terrestrial biomes appear to contribute 33 Gg yr−1 to the CH3I global budget.
Fractionation of lignin during leaching and sorption and implications for organic matter “freshness”
Authors: Hernes Peter J. , Robinson Amelia C. , Aufdenkampe Anthony K.
Published: September 2007

Much of what we know about the cycling of terrigenous organic matter (OM) in freshwater and marine systems can be attributed to evidence derived from biomarkers such as lignin. Here we report the fractionation of lignin phenols both during solubilization from plant litters and again during sorption of resulting leachates to soils. Source parameters in both leached and sorbed lignin varied from the parent litters by as much as ten‐fold, while elevated lignin oxidation parameters in riverine dissolved OM (DOM) can be completely explained by dissolution and sorption. Carbon‐normalized dissolved lignin endmembers indicate a substantial fraction of riverine DOM may not be vascular plant‐derived, and thus derived from algal, microbial or non‐vascular plant sources such as mosses. These results demonstrate that riverine DOM is less degraded and likely more labile than previously thought, and helps resolve the paradox of diagenetically‐altered riverine DOM degrading rapidly in marine systems.
Nonlinear rocket motor stability prediction: Limit amplitude, triggering, and mean pressure shift
Authors: Flandro Gary A. , Fischbach Sean R. , Majdalani Joseph
Published: September 2007

High-amplitude pressure oscillations in solid propellant rocket motor combustion chambers display nonlinear effects including: (1) limit cycle behavior in which the fluctuations may dwell for a considerable period of time near their peak amplitude, (2) elevated mean chamber pressure (DC shift), and (3) a triggering amplitude above which pulsing will cause an apparently stable system to transition to violent oscillations. Along with the obvious undesirable vibrations, these features constitute the most damaging impact of combustion instability on system reliability and structural integrity. The physical mechanisms behind these phenomena and their relationship to motor geometry and physical parameters must, therefore, be fully understood if instability is to be avoided in the design process, or if effective corrective measures must be devised during system development. Predictive algorithms now in use have limited ability to characterize the actual time evolution of the oscillations, and they do not supply the motor designer with information regarding peak amplitudes or the associated critical triggering amplitudes. A pivotal missing element is the ability to predict the mean pressure shift; clearly, the designer requires information regarding the maximum chamber pressure that might be experienced during motor operation. In this paper, a comprehensive nonlinear combustion instability model is described that supplies vital information. The central role played by steep-fronted waves is emphasized. The resulting algorithm provides both detailed physical models of nonlinear instability phenomena and the critically needed predictive capability. In particular, the origin of the DC shift is revealed.
On the vibronic coupling approximation: A generally applicable approach for determining fully quadratic quasidiabatic coupled electronic state Hamiltonians
Authors: Schuurman Michael S. , Yarkony David R.
Published: September 2007

In this report we introduce an iterative procedure for constructing a quasidiabatic Hamiltonian representing Nstate-coupled electronic states in the vicinity of an arbitrary point in Nint-dimensional nuclear coordinate space. The Hamiltonian, which is designed to compute vibronic spectra employing the multimode vibronic coupling approximation, includes all linear terms which are determined exactly using analytic gradient techniques. In addition, all [Nstate][Nint] quadratic terms, where [n]=n(n+1)∕2, are determined from energy gradient and derivative coupling information obtained from reliable multireference configuration interaction wave functions. The use of energy gradient and derivative coupling information enables the large number of second order parameters to be determined employing ab initio data computed at a limited number of points (Nint being minimal) and assures a maximal degree of quasidiabaticity. Numerical examples are given in which quasidiabatic Hamiltonians centered around three points on the C3H3N2 potential energy surface (the minimum energy point on the ground state surface and the minimum energy points on the two- and three-state seams of conical intersection) were computed and compared. A method to modify the conical intersection based Hamiltonians to better describe the region of the ground state minimum is introduced, yielding improved agreement with ab initio results, particularly in the case of the Hamiltonian defined at the two-state minimum energy crossing.
Use of helium nanodroplets for assembly, transport, and surface deposition of large molecular and atomic clusters
Authors: Mozhayskiy Vadim , Slipchenko Mikhail N. , Adamchuk Vera K. , Vilesov Andrey F.
Published: September 2007

The utility of continuous beam of helium droplets for assembly, transport, and surface deposition of metal and molecular clusters is studied. Clusters of propyne having from about 10to104molecules were obtained via sequential pickup of molecules by He droplets with average sizes in the range of 104–107 atoms. The maximum attainable flux of the propyne molecules carried by He droplets was found to be in the range of (5−15)×1015moleculessr−1s−1, being larger in larger droplets. The size of the clusters and the flux of the transported species are ultimately limited by the evaporative extinction of the entire helium droplet upon capture of particles. It is shown that the attenuation of the He droplet beam in the process of the cluster growth can be used in order to obtain the average size and the binding energy of the clusters. Furthermore, we used He droplets for assembling and surface deposition of gold and silver clusters having about 500 atoms. Typical deposition rate of metal atoms of about 3×1015atomssr−1s−1 is comparable to or larger than obtained with other beam deposition techniques. We propose that doping of He droplets by Au and Ag atoms in two separate pickup chambers leads to formation of the bimetal clusters having core-shell structure.
Vibrational spectroscopy of (SO42−)∙(H2O)n clusters, n=1–5: Harmonic and anharmonic calculations and experiment
Authors: Miller Yifat , Chaban Galina M. , Zhou Jia , Asmis Knut R. , Neumark Daniel M. , Benny Gerber R.
Published: September 2007

The vibrational spectroscopy of (SO42−)∙(H2O)n is studied by theoretical calculations for n=1–5, and the results are compared with experiments for n=3–5. The calculations use both ab initio MP2 and DFT/B3LYP potential energy surfaces. Both harmonic and anharmonic calculations are reported, the latter with the CC-VSCF method. The main findings are the following: (1) With one exception (H2O bending mode), the anharmonicity of the observed transitions, all in the experimental window of 540–1850cm−1, is negligible. The computed anharmonic coupling suggests that intramolecular vibrational redistribution does not play any role for the observed linewidths. (2) Comparison with experiment at the harmonic level of computed fundamental frequencies indicates that MP2 is significantly more accurate than DFT/B3LYP for these systems. (3) Strong anharmonic effects are, however, calculated for numerous transitions of these systems, which are outside the present observation window. These include fundamentals as well as combination modes. (4) Combination modes for the n=1 and n=2 clusters are computed. Several relatively strong combination transitions are predicted. These show strong anharmonic effects. (5) An interesting effect of the zero point energy (ZPE) on structure is found for (SO42−)∙(H2O)5: The global minimum of the potential energy corresponds to a Cs structure, but with incorporation of ZPE the lowest energy structure is C2v, in accordance with experiment. (6) No stable structures were found for (OH−)∙(HSO4−)∙(H2O)n, for n⩽5.
Pressure-induced reentrant micellization of amphiphilic block copolymers in dilute aqueous solutions
Authors: Osaka Noboru , Miyazaki Sho , Okabe Satoshi , Endo Hitoshi , Sasai Aya , Seno Ken-ichi , Aoshima Sadahito , Shibayama Mitsuhiro
Published: September 2007

The pressure-induced structural changes of a block copolymer, poly(2-ethoxyethoxyethyl vinyl ether)-block-poly(2-hydroxyethyl vinyl ether) (pEOEOVE-b-pHOVE) in aqueous solutions, were studied by means of small-angle neutron scattering (SANS) and dynamic light scattering (DLS) from atmospheric pressure up to 400MPa. pEOEOVE-b-pHOVE formed a spherical micellar structure above 40°C due to poor solubility of pEOEOVE. Micellization phase diagram was determined by DLS, and a covex-upward pressure-temperature (P-T) phase diagram was obtained having a peak around (P,T)=(150MPa,48°C). The SANS curves at 50°C were analyzed as a function of P. The micellar core size decreased by pressurizing at low P’s (P⩽150MPa) and then increased by further pressurizing (150MPa<P<400MPa). It was confirmed that the water volume fraction in the micellar core was larger at high P’s than that at low P’s even when the core sizes are the same at both pressure regions. This means that the temperature dependence of hydration is more selective at low pressures than at high pressures, in good accordance with our previous results on concentrated aqueous solutions of block copolymers [Phys. Rev. Lett. 96, 048303 (2006)].
Nonlinear responses of degenerate two-level systems to intense few-cycle pulses
Authors: Nagaya Kuninobu , Zhu Chaoyuan , Lin Sheng Hsien
Published: September 2007

Population transfers in degenerate (or almost degenerate) two-level systems interacting with the few-cycle laser pulse are investigated. A simple and analytical formula of nonadiabatic transition probability is derived with completely degenerate condition, demonstrating the sensitive dependence of the transition probability on the phase of the few-cycle pulses. As one of the applications of this formula, a new way of controlling the nuclear wave packet dynamics at a potential curve crossing by 1cycle laser pulse is proposed.
On the microscopic basis of Newton’s law of cooling and beyond
Authors: Nath Mihir Ranjan , Sen Surajit , Gangopadhyay Gautam
Published: September 2007

The microscopic basis of Newton’s law of cooling and its modification when the difference in temperature between the system and the surroundings is very large is discussed. When the system of interest is interacting with a small bath, the effect of the dynamical evolution of the bath variables is important to find out its dynamical feedback on the system. As in the usual system-bath approach, however, the bath is finally considered to be in thermal equilibrium and thereby provides an effective generalization of the Born-Markov master equation. It is shown that the cooling at early time is faster than that predicted by Newton’s law due to the dynamical feedback of the bath.
Toward the description of electrostatic interactions between globular proteins: Potential of mean force in the primitive model
Authors: Dahirel Vincent , Jardat Marie , Dufrêche Jean-François , Turq Pierre
Published: September 2007

Monte Carlo simulations are used to calculate the exact potential of mean force between charged globular proteins in aqueous solution. The aim of the present paper is to study the influence of the ions of the added salt on the effective interaction between these nanoparticles. The charges of the model proteins, either identical or opposite, are either central or distributed on a discrete pattern. Contrarily to Poisson–Boltzmann predictions, attractive, and repulsive direct forces between proteins are not screened similarly. Moreover, it has been shown that the relative orientations of the charge patterns strongly influence salt-mediated interactions. More precisely, for short distances between the proteins, ions enhance the difference of the effective forces between (i) like-charged and oppositely charged proteins, (ii) attractive and repulsive relative orientations of the proteins, which may affect the selectivity of protein/protein recognition. Finally, such results observed with the simplest models are applied to a more elaborate one to demonstrate their generality.
Two-stream instability, wave energy, and the energy principle
Authors: Lashmore-Davies C. N.
Published: September 2007

A generalized Poynting theorem for a system of uniform electron beams is obtained. Two examples of the two-stream instability with beams of equal density are used to discuss the relation between negative wave energy and negative potential energy, which arises in the energy principle of ideal magnetohydrodynamics. In the first example, v10>v20, while in the second example, v20=−v10, where v10,20 are the equilibrium beam velocities. Both cases can be interpreted in terms of the energy density arising from the generalized Poynting theorem. The first instability is due to the coupling of negative and positive energy waves at a frequency k(v10+v20)∕2. The second instability is due to the coupling of the same two perturbations, but at zero frequency. In this case, there is no oscillatory (wave) energy, but the beam electrons still make a negative contribution to the total energy.
Dimensional scaling treatment of stability of atomic anions induced by superintense, high-frequency laser fields
Authors: Wei Qi , Kais Sabre , Herschbach Dudley
Published: September 2007

We show that dimensional scaling, combined with the high-frequency Floquet theory, provides useful means to evaluate the stability of gas phase atomic anions in a superintense laser field. At the large-dimension limit (D→∞), in a suitably scaled space, electrons become localized along the polarization direction of the laser field. We find that calculations at large D are much simpler than D=3, yet yield similar results for the field strengths needed to bind an “extra” one or two electrons to H and He atoms. For both linearly and circularly polarized laser fields, the amplitude of quiver motion of the electrons correlates with the detachment energy. Despite large differences in scale, this correlation is qualitatively like that found between internuclear distances and dissociation energies of chemical bonds.
Essential energy space random walk via energy space metadynamics method to accelerate molecular dynamics simulations
Authors: Li Hongzhi , Min Donghong , Liu Yusong , Yang Wei
Published: September 2007

To overcome the possible pseudoergodicity problem, molecular dynamic simulation can be accelerated via the realization of an energy space random walk. To achieve this, a biased free energy function (BFEF) needs to be priori obtained. Although the quality of BFEF is essential for sampling efficiency, its generation is usually tedious and nontrivial. In this work, we present an energy space metadynamics algorithm to efficiently and robustly obtain BFEFs. Moreover, in order to deal with the associated diffusion sampling problem caused by the random walk in the total energy space, the idea in the original umbrella sampling method is generalized to be the random walk in the essential energy space, which only includes the energy terms determining the conformation of a region of interest. This essential energy space generalization allows the realization of efficient localized enhanced sampling and also offers the possibility of further sampling efficiency improvement when high frequency energy terms irrelevant to the target events are free of activation. The energy space metadynamics method and its generalization in the essential energy space for the molecular dynamics acceleration are demonstrated in the simulation of a pentanelike system, the blocked alanine dipeptide model, and the leucine model.
A model calculation of the tip field distribution for a single carbon nanotube
Authors: Shang X. F. , Wang M. , Qu S. , Ma Y. P. , Tan M. Q. , Xu Y. B. , Li Z. H.
Published: September 2007

In order to study the tip field of the carbon nanotube (CNT) or CNT array standing upright on a cathode plane, we proposed a model in which the long CNT is replaced by a floating top segment at the cathode potential. Using the fictitious charge and image method, a simple approximate formula for the field enhancement factor of a single CNT linear with the height-to-radius ratio has been deduced. This result is evidently improved compared to that from the floating sphere model. The normalized field strength distribution on the top hemisphere is also calculated and plotted, with the result depending slightly on the height-to-radius ratio. An estimation shows that the field emission intensity on the cylindrical surface of CNT is negligible compared to that on the top hemisphere.
Deposition and crystallization studies of thin amorphous solid water films on Ru(0001) and on CO-precovered Ru(0001)
Authors: Kondo Takahiro , Kato Hiroyuki S. , Bonn Mischa , Kawai Maki
Published: September 2007

The deposition and the isothermal crystallization kinetics of thin amorphous solid water (ASW) films on both Ru(0001) and CO-precovered Ru(0001) have been investigated in real time by simultaneously employing helium atom scattering, infrared reflection absorption spectroscopy, and isothermal temperature-programmed desorption. During ASW deposition, the interaction between water and the substrate depends critically on the amount of preadsorbed CO. However, the mechanism and kinetics of the crystallization of ∼50 layers thick ASW film were found to be independent of the amount of preadsorbed CO. We demonstrate that crystallization occurs through random nucleation events in the bulk of the material, followed by homogeneous growth, for solid water on both substrates. The morphological change involving the formation of three-dimensional grains of crystalline ice results in the exposure of the water monolayer just above the substrate to the vacuum during the crystallization process on both substrates.
Carrier capture in InGaAsSb∕InAs∕InGaSb type-II laser heterostructures
Authors: Shterengas L. , Kaspi R. , Ongstad A. P. , Suchalkin S. , Belenky G.
Published: September 2007

Experimental studies of the electron and hole concentration dynamics in the barrier of GaSb-based type-II quantum-well (QW) heterostructures were performed. Capture of electrons and holes was studied separately in specially designed and grown laser heterostructures with QWs only for electrons or only for holes. The difference between electron and hole relaxation rates is explained by corresponding QW carrier confinement energies.
Line shape studies of a state coupled to a random background including large fluctuations of the couplings
Authors: Dietz W. , Fischer Sighart F.
Published: September 2007

Line shape functions of a model system are analyzed, describing an oscillator carrying state coupled to background states randomly distributed in energy and with random coupling constants. Depending on the energy distribution functions or the nature of the coupling distribution, different line shape functions, such as the Lorentzian, the Fano, or that related to the nonexponential decay of the Förster type are recovered as limiting cases. Conditions for the range of applicability of a specially introduced mean square coupling approximation are derived. It is shown that the appearance of a Lorentzian line shape does not imply directly a homogeneous decay mechanism and that, on the other hand, commonly accepted conditions for the so-called statistical limit, expressed in terms of an average density and an average coupling, do not necessarily lead to a Lorentzian line shape. This is illustrated analytically through a model with randomly distributed transition dipolar couplings. Other applications relate to spectral diffusion in proteins and to bridged charge transfer.
Dependence of electron transfer among α cages on the chemical compositions of zeolite LTAs including K clusters
Authors: Kodaira Tetsuya , Murakami Yutaka
Published: September 2007

K atoms are loaded in diluted amount into K-form LTA zeolites whose framework compositions are AlxSi24−xO48 (6<x⩽12) per α cage. The optical and electron spin resonance (ESR) properties of K clusters formed in the α cages of the LTAs were investigated to elucidate the influence of the LTA compositions on the transfer of a 4s electron of a loaded K atom among the cages. Optical absorption spectra showed notable absorption at ∼1eV originating from cationic K clusters in the α cages independent of the x value. The linewidths of the ESR spectra showed a minimum value at x∼10. A motional narrowing effect induced by the electron transfer among the α cages is the origin of the sharp ESR spectra at x∼10. The gradual narrowing of the ESR spectral linewidth that occurred from x=12 to 10 can be explained with the assistance of numerical calculations of the periodic potential for an electron introduced into the LTAs. The potential inside the α cage becomes monotonously shallower with decreasing x value. On the other hand, the potential of an eight-membered ring shared with the adjacent α cages was insensitive to the x value. The calculation results demonstrate that the electron mobility becomes larger at smaller x values. The discrepancy between the actual ESR results and the calculation results for x<10 might be due to the aggregation of K+ ions to stabilize 4s electrons in the α cage in actual systems.
Photoinduced current transient spectroscopy of deep levels and transport mechanisms in iron-doped GaN thin films grown by low pressure-metalorganic vapor phase epitaxy
Authors: Muret P. , Pernot J. , Azize M. , Bougrioua Z.
Published: September 2007

Electrical transport and deep levels are investigated in GaN:Fe layers epitaxially grown on sapphire by low pressure metalorganic vapor phase epitaxy. Photoinduced current transient spectroscopy and current detected deep level spectroscopy are performed between 200 and 650 K on three Fe-doped samples and an undoped sample. A detailed study of the detected deep levels assigns dominant centers to a deep donor 1.39 eV below the conduction band edge EC and to a deep acceptor 0.75 eV above the valence band edge EV at low electric field. A strong Poole–Frenkel effect is evidenced for the donor. Schottky diodes characteristics and transport properties in the bulk GaN:Fe layer containing a homogenous concentration of 1019 Fe∕cm3 are typical of a compensated semiconductor. They both indicate that the bulk Fermi level is located typically 1.4 eV below EC, in agreement with the neutrality equation and dominance of the deep donor concentration. This set of results demonstrates unambiguously that electrical transport in GaN:Fe is governed by both types, either donor or acceptor, of the iron impurity, either substitutional in gallium sites or associated with other defects.
Morphological and magnetic properties of Co nanoparticle thin films grown on Si3N4
Authors: Presa B. , Matarranz R. , Clavero C. , García-Martín J. M. , Calleja J. F. , Contreras M. C.
Published: September 2007

The morphological and magnetic properties of Co nanoparticles deposited by triode sputtering on Si3N4 at 550°C are reported. The nominal thickness of Co ranges from 2 up to 15nm, and two different capping layers, Au and Pt, are used. The nanoparticles were characterized by x-ray diffraction and atomic force microscopy. Morphological and structural studies show that the nanoparticles grow in a well-defined nanostructured pattern and adopt a hexagonal closed packed crystalline structure. Moreover, the average particle size and the particle size dispersion increase as the thickness increases, due to percolation. Experimental characterization of effective anisotropy field was carried out with transverse susceptibility. Transverse susceptibility measurements reveal an in-plane isotropic magnetic behavior. Both the effective anisotropy field and the coercive field increase as the particle size increases, following a D6 dependence, which is typical for three-dimensional structures in the framework of the random anisotropy model. The relationship between the particle size distribution and the anisotropy field distribution is shown, explaining the significant dependence of the magnetic behavior on the Co layer thickness. On the other hand, different capping layers give rise to a change in the magnetic response due to the modification of the interparticle interaction.
Analyzing poly(3-hexyl-thiophene):1-(3-methoxy-carbonyl)propyl-1-phenyl-(6,6)C61 bulk-heterojunction solar cells by UV-visible spectroscopy and optical simulations
Authors: Sylvester-Hvid Kristian O. , Ziegler Tobias , Riede Moritz K. , Keegan Nicholas , Niggemann Michael , Gombert Andreas
Published: September 2007

A nondestructive method for assessing the thickness of the photoactive layer in poly(3-hexyl-thiophene):1-(3-methoxy-carbonyl)propyl-1-phenyl-(6,6)C61 (P3HT:PCBM) solar cells is reported. In the approach the absorption spectrum of the solar cell as derived by optical simulations is fitted to the corresponding measured spectrum, varying only the P3HT:PCBM layer thickness. Within the 50–250nm thickness range, a linear correlation between the position of a certain spectral minimum and the P3HT:PCBM layer thickness is shown, based on simulated absorption spectra. As an initial application, absorption spectra for 240 P3HT:PCBM solar cells prepared at four different spin-coating speeds were recorded, and the average P3HT:PCBM layer thickness estimated for each spin-coating speed. The simulated fraction of light absorbed in the P3HT:PCBM layer of the solar cells is compared with the P3HT:PCBM absorption spectra measured for films spin coated on simpler substrate types. The latter spectra cannot account for the light harvested in the photoactive layer of P3HT:PCBM solar cells because of substantial optical interference in the solar cells. The measured short circuit current densities Jsc for the solar cells vary with the spin-coating speed in a manner confirmed by optical simulations of the maximal short circuit current densities. The measured efficiencies follow the same pattern. On average the measured Jsc is 1–2mA∕cm2 below the simulated maximal short circuit current densities. Based on the resemblance of the measured and simulated absorption spectra such difference can be attributed to recombination exclusively.
Temperature dependent phase transition of EuO on MgO(100)
Authors: Lee Hangil , Kim J.-Y. , Rho K.-J. , Park B.-G. , Park J.-H.
Published: September 2007

We investigated the changes of magnetic properties and phase transition in EuO films grown on a MgO(100) substrate as a function of temperature. As the temperature was varied, we observed a clear phase transition and polarization change at 69K using spin resolved photoemission spectroscopy and low energy electron diffraction. We will elucidate the temperature driven changes in the electronic and magnetic properties of EuO films on a MgO(100) substrate.
Structural, magnetic, and transport investigations of CrTe clustering effect in (Zn,Cr)Te system
Authors: Sreenivasan M. G. , Teo K. L. , Cheng X. Z. , Jalil M. B. A. , Liew T. , Chong T. C. , Du A. Y. , Chan T. K. , Osipowicz T.
Published: September 2007

We investigate the structural, transport, and magnetic behaviors of (Zn,Cr)Te system without additional carrier doping grown by low temperature molecular-beam epitaxy on GaAs (100) substrates. For the growth of Zn1−xCrxTe with x=0.14, high-resolution transmission electron microscopy shows the possibility of zinc-blende (ZB)-CrTe phase being embedded in the Zn1−xCrxTe matrix. Our detailed analysis of the magnetization results in Zn0.86Cr0.14Te using scaling theory and modified Arrott plots suggests that the ferromagnetic ordering cannot be described by mean-field theory. Additionally, the resistivity behavior indicates that ZB-CrTe clusters could possibly provide a percolative conduction path that gives rise to high Curie temperature. We discussed the ferromagnetism in (Zn,Cr)Te system on the basis of clustering effect.
Low frequency picotesla field detection using hybrid MgO based tunnel sensors
Authors: Chaves R. C. , Freitas P. P. , Ocker B. , Maass W.
Published: September 2007

Low frequency ultrasensitive magnetic sensors are required for magnetocardiography (1pT at 10Hz) applications. MgO based magnetic tunnel junctions with RA=100–150Ωμm2 and tunnel magnetic resistance=100% were patterned into rectangular pillars with side up to 50μm. Sensors were incorporated in 500nm thick Co94Zr3Nb4 flux guides. Sensor linearization was achieved through internal (Co66Cr16Pt18 pads) and external (3.5mT) longitudinal bias fields resulting in sensitivities of 720%∕mT. Noise levels of 97pT∕Hz0.5 at 10Hz, 51pT∕Hz0.5 at 30Hz, and 2pT∕Hz0.5 at 500kHz were measured in the linear region of the transfer curve.
Correlation between bias stress instability and phototransistor operation of pentacene thin-film transistors
Authors: Debucquoy Maarten , Verlaak Stijn , Steudel Soeren , Myny Kris , Genoe Jan , Heremans Paul
Published: September 2007

The authors study the use of pentacene thin-film transistors as phototransistors. The shift in turn-on voltage (Von), responsible for the high photosensitivity of these devices, is shown to be strongly dependent on illumination time and applied gate voltage. The time dependence of this process is similar to the shift in Von during bias stress experiments in the dark, and illumination can simply be accounted for as an acceleration factor for bias stress instability. By comparing the characteristics of devices with different gate dielectrics, trapping of electrons by OH groups at the gate dielectric interface is indicated as a main origin for these shifts.
Resonance fluctuations of a whispering gallery mode biosensor by particles undergoing Brownian motion
Authors: Keng D. , McAnanama S. R. , Teraoka I. , Arnold S.
Published: September 2007

Nanoparticles suspended in the vicinity of a whispering gallery mode (WGM) biosensor are detected from fluctuations in the driving light-guide transmission. These fluctuations are described by Brownian particles perturbing the resonance wavelength in reaction to being polarized by the WGM’s evanescent field. Comparison between the autocorrelation of the measured fluctuations and theory provides a first order approximation for the nanoparticle size and lays the basis for future studies of interfacial dynamics. With this advance, the WGM biosensor goes beyond low-frequency measurements of adsorption and desorption and into a world which has been dominated by fluorescence correlation spectroscopy, but without labels.
Three-dimensional left-handed material lens
Authors: Petrov R. V. , Srinivasan G. , Bichurin M. I. , Viehland D.
Published: September 2007

A model is provided for the image formation by a three-dimensional lens with negative index of refraction (n) and compared with results for an array of split-ring resonators (SRRs) and wires. For n=−1, a linear decrease in image distance r is expected with increasing object distance l. A nonlinear r vs l is anticipated for other n values. A lens of an array of SRRs and wires was made and characterized over 1–18GHz and n=−1, and a gain of ∼8dB at 11.25GHz was achieved. Results on r vs l are in excellent agreement with the model.
Study of anomalous I-V characteristics in spatially confined manganite structures
Authors: Wu Jian-Chun , Sun Hua , Da Hai-Xia , Li Zhen-Ya
Published: September 2007

A random fuse network model is proposed to study the steplike negative differential resistance (NDR) in spatial confined manganite structures. Different underlying breaking processes due to self-heating effects are exhibited for various disorder strength of the networks. NDR multisteps are reproduced and the corresponding evolution of current morphology is present. Simulations results for the networks with various sizes show that confined geometry will sharpen the steplike NDR response in I-V curves, which agrees with experimental results well.
Density of InAs∕InP(001) quantum dots grown by metal-organic vapor phase epitaxy: Independent effects of InAs and cap-layer growth rates
Authors: Michon A. , Patriarche G. , Beaudoin G. , Saint-Girons G. , Gogneau N. , Sagnes I.
Published: September 2007

This letter studies and differentiates the influence of both InAs growth rate and cap-layer growth rate on the density of capped InAs∕InP(001) quantum dots (QDs) grown by metal-organic vapor phase epitaxy. The study shows that a decrease of the cap-layer growth rate leads to a reduction of the QD density. This reduction of QD density is of the same order as the kinetic reduction of QD density when decreasing InAs growth rate. Decreasing both InAs and cap-layer growth rates allows one to obtain a low density (9×107∕cm2) of QD emitting at around 1.55μm.
Efficient electron injection in organic light-emitting diodes using lithium quinolate/Ca∕Al cathodes
Authors: Kim Sung Hyun , Jang Jyongsik , Lee Jun Yeob
Published: September 2007

Device performances of green devices with cathode structure of lithium quinolate (Liq)∕Ca∕Al were investigated and electron injection mechanism was studied using ultraviolet photoelectron spectroscopy. Power efficiency could be improved by 70% by using Liq∕Ca∕Al cathode structure due to efficient electron injection, and interfacial energy barrier lowering by Liq∕Ca∕Al metal cathode was observed.
Photovoltaic effects in obliquely deposited oxygen-deficient manganite thin film
Authors: Yan Zijie , Yuan Xiao , Xu Yebin , Liu Liangqing , Zhang Xiang
Published: September 2007

Photovoltaic effects have been observed in oxygen-deficient La0.6Ca0.4MnO3−δ thin film obliquely deposited on Si substrate. The oxygen vacant sites can raise the photovoltaic sensitivity of the manganite thin film, and the photovoltaic sensitivities of 33.4V∕W and 2.84×105mV∕mJ are observed when the film is irradiated by a 635nm continuous wave laser and by a 532nm pulsed laser of 7ns duration, respectively. The open-circuit photovoltage of the film, when irradiated by the pulsed laser, has an abnormal change with a fast positive response of about 17ns and the change of voltage polarity after the laser pulse. It is found that the thickness of the film has important effects on the photoelectric characteristics and the abnormal photovoltage comes from the thickness difference.