bluuebunny/crossref_metadata_2025 huggingface dataset:
Placebo influences on dyskinesia in Parkinson's disease
Authors: Goetz Christopher G. , Laska Eugene , Hicking Christine , Damier Philippe , Müller Thomas , Nutt John , Warren Olanow C. , Rascol Olivier , Russ Hermann
Published: January 2008

Clinical features that are prognostic indicators of placebo response among dyskinetic Parkinson's disease patients were determined. Placebo‐associated improvements occur in Parkinsonism, but responses in dyskinesia have not been studied. Placebo data from two multicenter studies with identical design comparing sarizotan to placebo for treating dyskinesia were accessed. Sarizotan (2 mg/day) failed to improve dyskinesia compared with placebo, but both treatments improved dyskinesia compared with baseline. Stepwise regression identified baseline characteristics that influenced dyskinesia response to placebo, and these factors were entered into a logistic regression model to quantify their influence on placebo‐related dyskinesia improvements and worsening. Because placebo‐associated improvements in Parkinsonism have been attributed to heightened dopaminergic activity, we also examined the association between changes in Parkinsonism and dyskinesia. Four hundred eighty‐four subjects received placebo treatment; 178 met criteria for placebo‐associated dyskinesia improvement and 37 for dyskinesia worsening. Older age, lower baseline Parkinsonism score, and lower total daily levodopa doses were associated with placebo‐associated improvement, whereas lower baseline dyskinesia score was associated with placebo‐associated worsening. Placebo‐associated dyskinesia changes were not correlated with Parkinsonism changes, and all effects in the sarizotan group were statistically explained by the placebo‐effect regression model. Dyskinesias are affected by placebo treatment. The absence of correlation between placebo‐induced changes in dyskinesia and Parkinsonism argues against a dopaminergic activation mechanism to explain placebo‐associated improvements in dyskinesia. The magnitude and variance of placebo‐related changes and the factors that influence them can be helpful in the design of future clinical trials of antidyskinetic agents. © 2007 Movement Disorder Society
The DRD2 TaqIA polymorphism and demand of dopaminergic medication in Parkinson's disease
Authors: Paus Sebastian , Grünewald Anne , Klein Christine , Knapp Michael , Zimprich Alexander , Janetzky Bernd , Möller Jens C. , Klockgether Thomas , Wüllner Ullrich
Published: January 2008

Previous studies have demonstrated that the TaqIA polymorphism of the D2 dopamine receptor gene (DRD2) is associated with response to dopaminergic and antidopaminergic treatment in Parkinson's disease (PD) and schizophrenia, respectively. We tested whether the TaqIA genotype in PD is responsible for demand of dopaminergic medication, measured in total dopaminergic load per year of disease, in a large scale association study based on the gene bank of the German Competence Network on Parkinson's disease. Regression analysis yielded no significant differences between the TaqIA genotypes. We conclude that the DRD2 TaqIA polymorphism alone has no pivotal role for interindividual variability of dopaminergic requirement in PD. We propose a practicable system of measuring dopaminergic treatment for future pharmacogenetic studies in PD. © 2007 Movement Disorder Society
Are delayed‐start design trials to show neuroprotection in Parkinson's disease fundamentally flawed?
Authors: Clarke Carl E.
Published: January 2008

Considerable effort has gone into preclinical neuroprotection research in Parkinson's disease (PD) and several large clinical trials have been mounted, but no agent has been conclusively shown to be protective. The latest innovation in PD neuroprotection trial design is the delayed‐start design trial. If patients with early PD do better after 12 to 18 months of immediate drug therapy compared to those in whom it is delayed for 6 to 9 months, this is attributed to a neuroprotective effect. However, delayed‐start design trials may be fundamentally flawed. It has been suggested that physiological mechanisms compensating for the loss of dopaminergic neurones in early PD may be deleterious and that immediate treatment may prevent such mechanisms and thereby be neuroprotective. If this hypothesis is correct, any drug with a symptomatic effect will be neuroprotective in early PD and delayed‐start design trials will show this generic effect, not a neuroprotective effect specific to the drug. Delayed‐start design trials require patients to potentially stay untreated for 6 to 9 months. This may lead to the selection of slowly progressive types of PD, such as that in younger patients and those with tremor‐dominant disease, so the results may not be generalizable to the majority of patients. Delayed‐start design trials are powered to find small differences in total UPDRS score which may not be clinically significant; larger and longer placebo‐controlled trials are required to confirm the clinical significance of their findings. These arguments add to the growing tide of opinion for a fundamental rethink of our policy toward neuroprotection research in PD. © 2008 Movement Disorder Society
Estimating the extent of reporting to FDA: a case study of statin‐associated rhabdomyolysis
Authors: McAdams Mara , Staffa Judy , Dal Pan Gerald
Published: January 2008

Purpose

To estimate the extent of reporting to FDA through statin‐associated rhabdomyolysis data.

Methods

Data included incidence rates (IRs) of hospitalized rhabdomyolysis among statin users from a population‐based study, and comparable reported AERS cases and national estimates of statin use from an AERS analysis. Using IRs, national estimates of statin use and average days supply per prescription, we estimated the number of US statin‐associated cases of hospitalized rhabdomyolysis. We compared this estimate to the observed number of cases reported to FDA to evaluate the extent of reporting. We repeated this method for atorvastatin, cerivastatin, pravastatin, and simvastatin and statin combinations. We performed sensitivity analyses to check for biases such as misclassification of statin use and cohort selection bias. We evaluated potential time‐dependent cerivastatin reporting by a “Dear Health Care Provider (DHCP)” letter.

Results

The estimated extent of reporting to FDA varied by statin (atorvastatin, 5.0%; cerivastatin, 31.2%; simvastatin, 14.2%; all four combined, 17.7%; and non‐cerivastatin statins combined, 9.9%). No pravastatin‐associated cohort cases occurred. Across a reasonable value range, sensitivity analyses did not significantly alter the results; overall the cohort was similar to national statin‐users. There was a large increase in AERS reports after the cerivastatin DHCP letter and the estimated extent of reporting increased from 14.8 to 35.0%.

Conclusions

The extent of reporting of adverse events to FDA varied by statin and may be influenced by publicity. For statins‐associated rhabdomyolysis, the estimated extent of reporting appears to range from 5 to 30% but in the absence of stimulated reporting appears to be 5–15%. Copyright © 2008 John Wiley & Sons, Ltd.
Prediction of protein structure from ideal forms
Authors: Taylor William R. , Bartlett Gail J. , Chelliah Vijayalakshmi , Klose Daniel , Lin Kuang , Sheldon Tom , Jonassen Inge
Published: January 2008

For many years it has been accepted that the sequence of a protein can specify its three‐dimensional structure. However, there has been limited progress in explaining how the sequence dictates its fold and no attempt to do this computationally without the use of specific structural data has ever succeeded for any protein larger than 100 residues. We describe a method that can predict complex folds up to almost 200 residues using only basic principles that do not include any elements of sequence homology. The method does not simulate the folding chain but generates many thousands of models based on an idealized representation of structure. Each rough model is scored and the best are refined. On a set of five proteins, the correct fold score well and when tested on a set of larger proteins, the correct fold was ranked highest for some proteins more than 150 residues, with others being close topological variants. All other methods that approach this level of success rely on the use of templates or fragments of known structures. Our method is unique in using a database of ideal models based on general packing rules that, in spirit, is closer to an ab initio approach. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Multilevel Analysis of a Measure of Community Prevention Collaboration
Authors: Brown Eric C. , Hawkins J. David , Arthur Michael W. , Abbott Robert D. , Van Horn M. Lee
Published: January 2008

This study assesses a measure of community‐wide collaboration on prevention‐specific activities (i.e., prevention collaboration) in context of the theory of community change used in the Communities That Care prevention system. Using data from a sample of 599 community leaders across 41 communities, we examined the measure with regard to its factor structure, associations with other concurrent community‐level measures, and prediction by individual‐ and community‐level characteristics. Results of multilevel confirmatory factor analysis provide evidence for the construct validity of the measure and indicate significant (p < .05) associations with concurrent validity criteria. Female community leaders reported significantly higher levels of prevention collaboration and community leaders sampled from religious organizations reported lower levels of prevention collaboration than did their respective counterparts. Although no community‐level characteristics were associated significantly with prevention collaboration, community clustering accounted for 20–28% of the total variation in the measure. Findings support the use of this measure in assessing the importance of collaboration in community‐based prevention initiatives.
Synthesis, Surface‐Active Properties, and Antimicrobial Activities of New Neutral and Cationic Trimeric Surfactants
Authors: Murguía Marcelo C. , Cristaldi Mariano D. , Porto Ayelén , di Conza José , Grau Ricardo J.
Published: January 2008

Neutral and cationic series of new trimeric β‐hydroxy amino or ammonium surfactants were synthesized via a two‐step process involving the Williamson etherification and regioselective oxirane ring opening with primary and tertiary amines, which afforded good to excellent yields. The synthesized compounds were obtained in high purity by a simple purification procedure on column chromatography. The critical micelle concentration (CMC), effectiveness of surface tension reduction (γCMC), surface excess concentration (Γ), and area per molecule at the interface (A) were determined and values indicate that the cationic series is characterized by good surface‐active and self‐aggregation properties. The antimicrobial activities are reported for the first time against representative bacteria and fungi for trimeric compounds. The antimicrobial potency was found to be dependent on the target microorganism (Gram‐positive bacteria > fungi > Gram‐negative bacteria), as well as both the neutral or ionic nature (cationic > neutral) and alkyl chain length (tri‐C12 > tri‐C18 > tri‐C8) of the compounds. The tri‐C8 and tri‐C18 compounds were found to be almost inactive and the tri‐C12 compounds, the most potent antimicrobial surface‐active agents from the synthesized series. The trimeric C12 cationic compound was found to be comparable to benzalkonium chloride against Gram‐positive bacteria and fungi, in vitro. The antimicrobial effectiveness of this new compound and the facile two‐step procedure for synthesizing it with an excellent overall yield (92%) provide a cost effective trimeric gemini surfactant.
Kinetic Parameters of a Homogeneous Transmethylation of Soybean Oil
Authors: Doell Ryan , Konar Samir K. , Boocock David G. B.
Published: January 2008

The kinetic parameters of a truly homogeneous base‐catalyzed transmethylation of soybean oil at four temperatures from 23 to 50 °C have been determined for the first time. The addition of oxolane, as well as a high methanol/oil molar ratio (27:1), was used to achieve and maintain a monophasic system throughout the reactions. Second order rate constants were determined in terms of the concentrations of the mechanistic reactants, which were the glycerides and methoxide ions (and not methanol). Doubling the methoxide concentration increased the reaction rate twofold. At 23 °C the rate constants for the conversion of triglycerides to diglycerides, diglycerides to monoglycerides, and monoglycerides to glycerol were 6.3, 15.3 and 13.0 L mol−1 min−1, respectively. These increased to 54.2, 136 and 139 L mol−1 min−1 at 50°C. These latter values (adjusted to 60 °C) were 65, 770 and 190 times larger, respectively, than values cited previously (and adjusted to the methoxide basis) for a transmethylation of Pongamia oil, which was also claimed to be homogeneous. Activation energies for all three steps were the same (63 kJ mol−1). Pre‐exponential factors showed that in diglycerides and triglycerides the second and third ester chains sterically hindered the attack of methoxide ions on the ester carbonyl groups.
Heat shock protein 90 regulates stabilization rather than activation of soluble guanylate cyclase
Authors: Nedvetsky Pavel I. , Meurer Sabine , Opitz Nils , Nedvetskaya Tatiana Y. , Müller Helmut , Schmidt Harald H.H.W.
Published: January 2008

Endothelium‐derived nitric oxide (NO) activates the heterodimeric heme protein soluble guanylate cyclase (sGC) to form cGMP. In different disease states, sGC levels and activity are diminished possibly involving the sGC binding chaperone, heat shock protein 90 (hsp90). Here we show that prolonged hsp90 inhibition in different cell types reduces protein levels of both sGC subunits by about half, an effect that was prevented by the proteasome inhibitor MG132. Conversely, acute hsp90 inhibition affected neither basal nor NO‐stimulated sGC activity. Thus, hsp90 is a molecular stabilizer for sGC tonically preventing proteasomal degradation rather than having a role in short‐term activity regulation.
Induction of podoplanin by transforming growth factor‐β in human fibrosarcoma
Authors: Suzuki Hiroyuki , Kato Yukinari , Kaneko Mika Kato , Okita Yukari , Narimatsu Hisashi , Kato Mitsuyasu
Published: January 2008

Podoplanin/aggrus is increased in tumors and its expression was associated with tumor malignancy. Podoplanin on cancer cells serves as a platelet‐aggregating factor, which is associated with the metastatic potential. However, regulators of podoplanin remain to be determined. Transforming growth factor‐β (TGF‐β) regulates many physiological events, including tumorigenesis. Here, we found that TGF‐β induced podoplanin in human fibrosarcoma HT1080 cells and enhanced the platelet‐aggregating‐ability of HT1080. TGF‐β type I receptor inhibitor (SB431542) and short hairpin RNAs for Smad4 inhibited the podoplanin induction by TGF‐β. These results suggest that TGF‐β is a physiological regulator of podoplanin in tumor cells.
Effects of seasonality, litter removal and dry-season irrigation on litterfall quantity and quality in eastern Amazonian forest regrowth, Brazil
Authors: Vasconcelos Steel Silva , Zarin Daniel Jacob , Araújo Maristela Machado , Rangel-Vasconcelos Lívia Gabrig Turbay , de Carvalho Cláudio José Reis , Staudhammer Christina Lynn , Oliveira Francisco de Assis
Published: January 2008

Litterfall quantity and quality may respond to alterations in resource availability expected with ongoing land-use and climate changes. Here, we quantify the effects of altered resource availability on non-woody litterfall quantity and quality (nitrogen and phosphorus concentrations) in eastern Amazonian forest regrowth (Brazil) through two multi-year experimental manipulations: (1) daily irrigation (5 mm d−1) during the dry season; and (2) fortnightly litter removal. Consistent with other tropical forest data litterfall exhibited seasonal patterns, increasing with the onset of the dry season and declining with the onset of the rainy season. Irrigation did not affect litterfall mass and had little impact on nitrogen (N) or phosphorus (P) concentrations and return, except for decreasing litter P concentration at the end of two irrigation periods. Litter removal did not alter litterfall mass or P concentration, but progressively reduced litterfall N during the course of the experiment. Overall, these results suggest significant resistance to altered resource availability within the bounds of our experimental treatments; our findings may help to constrain carbon and nutrient cycling predictions for tropical forests in response to land-use and climate changes.
Repeated disturbances and canopy disturbance regime in a tropical semi-deciduous forest
Authors: de Lima Renato A. Ferreira , Martini Adriana M. Zanforlin , Gandolfi Sérgius , Rodrigues Ricardo Ribeiro
Published: January 2008

The canopy disturbance regime and the influence of gap methods on the interpretation of forest structure and dynamics were evaluated in a tropical semi-deciduous forest in south-eastern Brazil. We encountered a gap density of 11.2 gaps ha−1and an average size which varied from 121 to 333 m2depending on the gap delimitation method considered (minimum gap size was 10 m2). Although average size was slightly higher, the median value obtained (78 m2) was comparable to other tropical forest sites and the gap size-class distribution found supported the pattern described for such forest sites. Among 297 gap makers, snapping and uprooting were the most common modes of disturbance. The number and basal area of gap makers were good predictors of gap size. Almost 25% of all gaps suffered from repeated disturbance events that brought about larger gap sizes. Such processes, along with delimitation methods, strongly influenced the estimation of turnover rate and therefore the interpretation of forest dynamics. These results demonstrated the importance of further studies on repeated disturbances, which is often neglected in forest studies.
δ13C inPentaclethra macrolobatrees growing at forest edges in north-eastern Costa Rica
Authors: Schedlbauer Jessica L. , Kavanagh Kathleen L.
Published: January 2008

Fragmented forest landscapes with large proportions of edge area are common in the tropics, though little is known about functional responses of trees to edge effects. Foliar δ13C can increase our understanding of tree function, as these values reflect changes in ci/caas trees respond to environmental gradients. We expected that foliar δ13C would be enriched, indicating a decline in ci/ca, inPentaclethra macrolobatrees growing at forest edges in north-eastern Costa Rica. We also anticipated this isotopic shift in δ13C values of soil carbon and soil respired CO2. Three transects perpendicular to forest edges were established at three study sites, and six plots per transect were located 0–300 m from edges. Within plots, foliage, soil and soil respired CO2were collected for isotopic analyses. Foliar δ13C, thus ci/ca, and soil carbon δ13C did not vary along the edge to interior gradient. δ13C for canopy and understorey foliage averaged −29.7‰ and −32.5‰, respectively, while soil carbon δ13C averaged −28.0‰. Soil respired CO2δ13C ranged from −29.2‰ to −28.6‰ and was significantly depleted within 50 m of edges. The predominant lack of functional responses at forest edges indicates thatP. macrolobatrees are robust and these forests are minimally influenced by edge effects.
Spatial Resolution and Information Transfer in Scanning Transmission Electron Microscopy
Authors: Peng Yiping , Oxley Mark P. , Lupini Andrew R. , Chisholm Matthew F. , Pennycook Stephen J.
Published: January 2008

The relation between image resolution and information transfer is explored. It is shown that the existence of higher frequency transfer in the image is just a necessary but not sufficient condition for the achievement of higher resolution. Adopting a two-point resolution criterion, we suggest that a 10% contrast level between two features in an image should be used as a practical definition of resolution. In the context of scanning transmission electron microscopy, it is shown that the channeling effect does not have a direct connection with image resolution because sharp channeling peaks do not move with the scanning probe. Through a quantitative comparison between experimental image and simulation, a Fourier-space approach is proposed to estimate defocus and sample thickness. The effective atom size inZ-contrast imaging depends on the annular detector's inner angle. Therefore, an optimum angle exists for the highest resolution as a trade-off between reduced atom size and reduced signal with limited information transfer due to noise.
Evidence for atmospheric variability over the Pacific on decadal timescales
Authors: Burgman R. J. , Clement A. C. , Mitas C. M. , Chen J. , Esslinger K.
Published: January 2008

An index of Pacific decadal variability based on a multivariate empirical orthogonal function analysis of National Centers for Environmental Prediction reanalysis is used to extract associated signals in satellite‐based measurements of atmospheric parameters. This index captures the 1976–1977 “El Niño–Southern Oscillation (ENSO)‐like” warming shift of sea surface temperatures (SST) as well as a more recent transition of opposite sign in the 1990s. Utilizing measurements of water vapor, wind speed, precipitation, long‐wave radiation, as well as surface observations, our analysis shows evidence of the atmospheric changes in the mid‐1990s that accompanied the “ENSO‐like” interdecadal SST changes.
Late Pleistocene slip rate along the Owens Valley fault, eastern California
Authors: Kirby Eric , Anandakrishnan Sridhar , Phillips Fred , Marrero Shasta
Published: January 2008

The Owens Valley fault zone (OVF) is one of the primary structures accommodating dextral shear across the Eastern California shear zone (ECSZ). Previous estimates of the Holocene slip rate along this structure rely on paleoseismic data and yield rates 2–3 times lower than those implied by geodetic velocities. Using displaced lava flows along the flank of Crater Mountain, we present the first estimate of slip rate along the OVF during the late Pleistocene. Subsurface characterization of the flow margin using a ground‐penetrating radar (GPR) allows for relatively precise determination of dextral displacement, and terrestrial cosmogenic 36Cl exposure ages of samples from the flow surface yield slip rates between ∼2.8 – 4.5 mm/yr over the past 55–80 kyr. Our results suggest either that paleoseismic slip‐rate estimates underestimate the long‐term slip rate or that rates of strain release have not been steady during the latter part of the Quaternary.
Extracting the 2004 Indian Ocean tsunami signals from sea surface height data observed by satellite altimetry
Authors: Hayashi Y.
Published: January 2008

Altimeter‐equipped satellites flew over the propagating area of the Indian Ocean tsunami caused by the 2004 Sumatra‐Andaman earthquake on 26 December 2004. Tsunami signals can be detected as differences in sea level changes of multiple tracks. However, observed changes in sea level differences involve not only tsunami signals but also effects from various ocean phenomena and errors due to observation technology and data processing. A multisatellite time‐spatial interpolation method is performed to define reference sea surface heights. After applying the method to the products on sea level anomalies along tracks of altimeter‐equipped satellites, quality tsunami‐height profiles with only 4‐ to 5‐cm root mean square errors were obtained for the Indian Ocean tsunami along five tracks from four satellites (Jason‐1, TOPEX/POSEIDON, ENVISAT, and Geosat Follow‐On). Maximum tsunami height in the open ocean for the 2004 Indian Ocean tsunami as observed from satellite altimetry was 1.1 m trough‐to‐crest 115 min after the main shock. Reliable tsunami‐height profiles from satellite altimetry were extracted for the first time. The method employed in this study has the potential to extract tsunami signals of 0.1 m or greater trough‐to‐crest height from satellite altimetry observation data on the deep sea by ongoing satellite missions.
When is H2O not water?
Authors: Pickard Chris J. , Needs R. J.
Published: January 2008

We have combined a computational search strategy with first-principles density-functional-theory calculations to identify metastable phases of H2O under pressure. The most stable structures consist of water molecules, while the most energetic metastable phases consist of oxygen and hydrogen molecules. In between lie many other metastable phases, consisting of various combinations of a few small molecules. It may be possible to synthesize some of these metastable phases, and we use our results to understand the nature of the crystalline metastable phase of H2O recently synthesized by Mao et al. [Science 314, 636 (2006)].
Accurate quantum mechanical calculations of differential and integral cross sections and rate constant for the O+OH reaction using an ab initio potential energy surface
Authors: Lin Shi Ying , Guo Hua , Honvault Pascal , Xu Chuanxiu , Xie Daiqian
Published: January 2008

The authors report accurate quantum mechanical studies of the O+OH reaction on the improved Xu-Xie-Zhang-Lin-Guo potential energy surface. The differential cross section was obtained at several energies near the reaction threshold using a time-independent method. The dominant forward and backward peaks in the angular distribution are consistent with a complex-forming mechanism, which is also confirmed by the extensive rotational excitation in the O2 product. However, the asymmetry of these peaks suggests a significant nonstatistical component. The initial state (υi=0, ji=0) specified integral cross section, which was calculated up to 1.15eV of collision energy using the Chebyshev wave packet method, shows no energy threshold and decreases with the increasing collision energy, consistent with the barrierless nature of the reaction. The resulting rate constant exhibits a negative temperature dependence for T>100K and decays as the temperature is lowered, in qualitative agreement with available experimental data.
A high-resolution near-edge x-ray absorption fine structure investigation of the molecular orientation in the pentacene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) pentacene/system
Authors: Casu M. B. , Cosseddu P. , Batchelor D. , Bonfiglio A. , Umbach E.
Published: January 2008

We present x-ray photoemission spectroscopy and highly resolved near-edge x-ray absorption fine structure spectroscopy measurements taken on pentacene thin films of different thicknesses deposited on a spin coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) substrate. Thin films of pentacene were prepared by using organic molecular beam deposition in situ using strictly controlled evaporation conditions. Our investigations show that pentacene thin films on PEDOT:PSS are characterized by upright standing molecules. Due to the strong dichroic behavior, the calculated values of the molecular orientation give a clear indication not only of the real molecular arrangement in the films but also of a high orientational order. This high degree of molecular orientation order is a characteristic already of the first layer. The films show the tendency to grow on the PEDOT:PSS substrate following an island-fashion mode, with a relatively narrow intermixing zone at the interface between the pentacene and the polymer blend. The peculiarity of the growth of pentacene on PEDOT:PSS is due to the fact that the substrate does not offer any template for the nucleated films and thus exerts a lateral order toward the crystal structure arrangement. Under these conditions, the upright orientation of the molecules in the films minimizes the energy required for the system stability.
Kinetics of autocatalysis in small systems
Authors: Arslan Erdem , Laurenzi Ian J.
Published: January 2008

Autocatalysis is a ubiquitous chemical process that drives a plethora of biological phenomena, including the self-propagation of prions etiological to the Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. To explain the dynamics of these systems, we have solved the chemical master equation for the irreversible autocatalytic reaction A+B→2A. This solution comprises the first closed form expression describing the probabilistic time evolution of the populations of autocatalytic and noncatalytic molecules from an arbitrary initial state. Grand probability distributions are likewise presented for autocatalysis in the equilibrium limit (A+B⇌2A), allowing for the first mechanistic comparison of this process with chemical isomerization (B⇌A) in small systems. Although the average population of autocatalytic (i.e., prion) molecules largely conforms to the predictions of the classical “rate law” approach in time and the law of mass action at equilibrium, thermodynamic differences between the entropies of isomerization and autocatalysis are revealed, suggesting a “mechanism dependence” of state variables for chemical reaction processes. These results demonstrate the importance of chemical mechanism and molecularity in the development of stochastic processes for chemical systems and the relationship between the stochastic approach to chemical kinetics and nonequilibrium thermodynamics.
Giant resonant magneto-optic Kerr effect in nanostructured ferromagnetic metamaterials
Authors: Zharov Alexander A. , Kurin Vladislav V.
Published: January 2008

We show that the magneto-optic Kerr effect can be significantly enhanced in composite nanostructured metamaterials due to plasmon dipole resonance of individual particles making up the composite. We find that in contrast to continuous ferromagnetic medium nanostructured film possesses a nontrivial frequency-dependent optical response which can be potentially used for data recording and processing as well as for diagnostics of magnetization state of composite ferromagnetic films.
Investigation on switching kinetics in epitaxial Pb(Zr0.2Ti0.8)O3 ferroelectric thin films: Role of the 90° domain walls
Authors: Li Wei , Alexe Marin
Published: January 2008

Ferroelectric switching behavior of single-crystal-like epitaxial Pb(Zr0.2Ti0.8)O3 thin films with different densities of 90° domain walls was investigated under various applied fields. It was found that the saturated switchable polarization of about 170μC∕cm2 did not vary with applied field in the films with low density or no 90° domain walls and obeys Kolmogorov-Avrami-Ishibashi theory. The presence of the 90° domain walls inhibits the motion of 180° domain walls, contributing to the change of the switching kinetics to nucleation-limited-switching model.
Investigation of nonlinear dielectric properties in Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films
Authors: de Los S. Guerra J. , Mendes R. G. , Eiras J. A. , Santos I. A. , Araújo E. B.
Published: January 2008

The ac and dc driving fields dependence of the dielectric permittivity for the strontium barium niobate relaxor ferroelectric thin films has been investigated. The nonlinear dielectric properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the ac and dc “bias” electric field amplitude in wide frequency (100Hz–10MHz) and temperature (50–450K) intervals. The results hint the existence of a true mesoscopic dielectric relaxor response in the ferroelectric thin film, which is very similar to those observed in bulk relaxor ferroelectrics. An anomalous behavior of the NL dielectric response was observed when submitted to moderate dc electric fields levels, indicating a crossover from paraelectric to a glasslike behavior on cooling the sample toward the freezing transition. The obtained results were analyzed within the framework of the models proposed in the current literature.
Raman spectroscopic determination of hole concentration in p-type GaSb
Authors: Maslar J. E. , Hurst W. S. , Wang C. A.
Published: January 2008

Phonon-plasmon coupled mode Raman spectra of p-type GaSb were measured at room temperature as a function of hole concentration. These spectra were obtained using an optical system based on 752.55nm excitation in order to obtain more sensitivity to bulk GaSb coupled mode Raman scattering than is possible with visible wavelength excitation-based systems. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated for determination of hole concentration from the bulk coupled mode spectra. The hole concentration was determined from the Raman spectra by minimizing the sum of the squared residuals between a measured and simulated spectrum as a function of total hole concentration and a plasmon damping parameter. The hole concentrations determined from the fit to the Raman spectra were compared to the hole concentrations determined from single magnetic field Hall effect measurements that were corrected to account for two band conduction. The hole concentrations determined using the two methods differed by ≈3% to ≈33% for single magnetic field Hall effect hole concentrations from ≈5.51×1017to≈6.38×1018cm−3. The agreement between the hole concentrations determined using the two methods was worse for single magnetic field Hall effect hole concentrations below ≈5.51×1017cm−3. In general, compared to the hole concentrations determined from Hall effect measurements corrected to account for two band conduction, the hole concentrations determined from the Raman spectra were higher for epilayers with the lower Hall effect hole concentrations and lower for the epilayer with the highest Hall effect hole concentration. The deviations between the two methods were attributed to the limitations of the spectral model employed and uncertainties in GaSb materials properties.
Distinct processes in radio-frequency reactive magnetron plasma sputter deposition of silicon suboxide films
Authors: van Hattum E. D. , Palmero A. , Arnoldbik W. M. , Rudolph H. , Habraken F. H. P. M.
Published: January 2008

A detailed investigation of the distinct processes in radio-frequency reactive magnetron plasma sputter deposition of SiOx films in a O2∕Ar atmosphere has been carried out, using the experimental evaluation of the individual growth rates of silicon and oxygen and of the ion impingement on the growth surface. Experimental variables are the total pressure, the oxygen partial pressure necessary to grow layers with 0⩽x⩽2, the RF power, the substrate temperature during deposition and the height of the cathode with respect to the growth surface. The various possible contributions to the silicon and oxygen incorporation on the growth surface have been distinguished and the magnitude of their contribution estimated, including that of sputtered SiO molecules. A model concerning the oxygen coverage on the cathode erosion area during sputtering is discussed, including the transition from the metallic cathode to the poisoned, nonmetallic, cathode.
Mechanical behavior of gallium nitride nanotubes under combined tension-torsion: An atomistic simulation
Authors: Wang Zhiguo , Zu Xiaotao , Gao Fei , Weber William J.
Published: January 2008

The tensile mechanical behavior of single crystalline gallium nitride (GaN) nanotubes under combined tension-torsion is investigated using molecular dynamics simulations with an empirical potential. The simulation results show that a small torsion rate (<0.010degps−1) does not affect the tensile behavior of GaN nanotube, i.e., the nanotubes show brittle properties at low temperatures; whereas at high temperatures, they behave as ductile materials. However, the failure stress decreases with increasing rate of torsion above 0.010degps−1, and the nanotube fails in a different manner. The torsion rate has no effect on the elastic properties of GaN nanotubes.
Characterization of large cadmium zinc telluride crystals grown by traveling heater method
Authors: Chen H. , Awadalla S. A. , Iniewski K. , Lu P. H. , Harris F. , Mackenzie J. , Hasanen T. , Chen W. , Redden R. , Bindley G. , Kuvvetli Irfan , Budtz-Jørgensen Carl , Luke P. , Amman M. , Lee J. S. , Bolotnikov A. E. , Camarda G. S. , Cui Y. , Hossain A. , James R. B.
Published: January 2008

The focus of this paper is to evaluate thick, 20×20×10 and 10×10×10mm3, cadmium zinc telluride (CZT), Cd0.9Zn0.1Te, crystals grown using the traveling heater method (THM). The phenomenal spectral performance and small size and low concentration of Te inclusions/precipitates of these crystals indicate that the THM is suitable for the mass production of CZT radiation detectors that can be used in a variety of applications. Our result also proves that with careful material selection using IR and high-quality fabrication processes, the theoretical energy resolution limit can be achieved.
Quantum dynamics of coupled translational and rotational motions of H2 inside C60
Authors: Xu Minzhong , Sebastianelli Francesco , Bačić Zlatko , Lawler Ronald , Turro Nicholas J.
Published: January 2008

We report rigorous quantum calculations of the translation-rotation (T-R) eigenstates of the H2 molecule in C60. The resulting level structure can be explained in terms of a few dominant features. These include the coupling between the orbital and the rotational angular momenta of H2 to give the total angular momentum λ, and the splitting of the sevenfold degeneracy of T-R levels with λ=3 by the nonsphericity of C60, according to the rules of the icosahedral Ih group.
Epitaxial La2Hf2O7 thin films on Si(001) substrates grown by pulsed laser deposition for high-k gate dielectrics
Authors: Wei Feng , Tu Hailing , Wang Yi , Yue Shoujing , Du Jun
Published: January 2008

The La2Hf2O7 (LHO) films have been epitaxially grown on Si(001) substrates using an ultrahigh vacuum pulsed laser deposition system. X-ray diffraction characterization shows the predominant orientation of the LHO film grown at 780°C is (001)LHO∥(001)Si and [110]LHO∥[110]Si. High-resolution transmission electron microscopy results illustrate that the epitaxial LHO film with high crystallinity is in pure pyrochlore phase and has an unobservable interfacial layer between Si and LHO. The electrical characterization of metal-insulator-semiconductors reveals that the epitaxial LHO film has a dielectric constant of approximately 22, an acceptable gate leakage current density and a negligible hysteresis in capacitance-voltage characterization.
Deformation-induced grain rotation and growth in nanocrystalline Ni
Authors: Wang Y. B. , Li B. Q. , Sui M. L. , Mao S. X.
Published: January 2008

Nanobeam electron diffraction and a series of dark field images techniques were used to investigate the deformation mechanisms of nanocrystalline (nc) Ni in response to in situ tensile deformation under transmission electron microscopy (TEM). The experiments exhibit the complete processes of individual grain rotation and neighboring grain rotation/growth. Deformation-induced grain rotation and growth as one of plastic deformation mechanisms in nc materials was revealed. At the same time, these results were confirmed further by ex situ TEM observation on deformed sample and were also better understood by physical deformation model.
High energy density metal-insulator-metal capacitors with Ba[(Ni1∕2,W1∕2)0.1Ti0.9]O3 thin films
Authors: Karan N. K. , Saavedra-Arias J. J. , Perez M. , Thomas R. , Katiyar R. S.
Published: January 2008

Metal-insulator-metal capacitors with high-k Ba[(Ni1∕2,W1∕2)0.1Ti0.9]O3 thin film dielectrics were fabricated by chemical solution deposition technique. High dielectric constant (85), low dielectric loss (0.007), and high breakdown field (∼3.0MV∕cm) at room temperature were achieved. The temperature and frequency dependences of capacitance and loss tangent were small around room temperature (300±25K). At room temperature, high capacitance density (3.1fF∕μm2) along with high energy density (34J∕cm3) and low leakage current (7.7×10−6A∕cm2 at 20V) were obtained, indicating high potential for this material in the integrated circuits and power electronic applications.
Optical beam focusing by a single subwavelength metal slit surrounded by chirped dielectric surface gratings
Authors: Kim Seyoon , Lim Yongjun , Kim Hwi , Park Junghyun , Lee Byoungho
Published: January 2008

A method for optical beam focusing by a single subwavelength metal slit surrounded by surface gratings is proposed. In our proposed method, the period of each surface grating is chirped so that the radiation fields of surface plasmon polaritons can be controlled to make a beam spot at the desired focal length. Through our proposed method, it is numerically shown that we can make a beam spot which is located at the several times of wavelength distance from the slit, and its focal length can be controlled.
Reflow dynamics of thin patterned viscous films
Authors: Leveder T. , Landis S. , Davoust L.
Published: January 2008

This letter presents a study of viscous smoothening dynamics of a nanopatterned thin film. Ultrathin film manufacturing processes appearing to be a key point of nanotechnology engineering and numerous studies have been recently led in order to exhibit driving parameters of this transient surface motion, focusing on time scale accuracy method. Based on nanomechanical analysis, this letter shows that controlled shape measurements provided much more detailed information about reflow mechanism. Control of reflow process of any complex surface shape, or measurement of material parameter as thin film viscosity, free surface energy, or even Hamaker constant are therefore possible.
Selective photoinactivation of protein function through environment-sensitive switching of singlet oxygen generation by photosensitizer
Authors: Yogo Takatoshi , Urano Yasuteru , Mizushima Akiko , Sunahara Hisato , Inoue Takanari , Hirose Kenzo , Iino Masamitsu , Kikuchi Kazuya , Nagano Tetsuo
Published: January 2008

Chromophore-assisted light inactivation is a promising technique to inactivate selected proteins with high spatial and temporal resolution in living cells, but its use has been limited because of the lack of a methodology to prevent nonspecific photodamage in the cell owing to reactive oxygen species generated by the photosensitizer. Here we present a design strategy for photosensitizers with an environment-sensitive off/on switch for singlet oxygen (
1
O
2
) generation, which is switched on by binding to the target, to improve the specificity of protein photoinactivation.
1
O
2
generation in the unbound state is quenched by photoinduced electron transfer, whereas
1
O
2
generation can occur in the hydrophobic environment provided by the target protein, after specific binding. Inositol 1,4,5-trisphosphate receptor, which has been suggested to have a hydrophobic pocket around the ligand binding site, was specifically inactivated by an environment-sensitive photosensitizer-conjugated inositol 1,4,5-trisphosphate receptor ligand without
1
O
2
generation in the cytosol of the target cells, despite light illumination, demonstrating the potential of environment-sensitive photosensitizers to allow high-resolution control of generation of reactive oxygen species in the cell.
Evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of
zen
Authors: Rafiqi Ab. Matteen , Lemke Steffen , Ferguson Sean , Stauber Michael , Schmidt-Ott Urs
Published: January 2008

Higher cyclorrhaphan flies including
Drosophila
develop a single extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle
Tribolium
and in the milkweed bug
Oncopeltus
, the homeobox gene
zerknüllt
(
zen
) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of
zen
in the extraembryonic tissue of lower Cyclorrhapha. We show that
Megaselia abdita
(Phoridae) and
Episyrphus balteatus
(Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using
Krüppel
(
Kr
) and
pannier
(
pnr
) homologues of
Megaselia
as markers for serosal and amniotic tissue, respectively, we show that after
zen
RNAi all extraembryonic tissue becomes indistinguishable from amniotic cells, like in
Tribolium
but unlike in
Drosophila
, in which
zen
controls all aspects of extraembryonic development. Compared with
Megaselia
and
Episyrphus
,
zen
expression in
Drosophila
is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct extraembryonic tissue organizations and the conserved requirement of
zen
for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of
zen
.
A continuous hyperchromicity assay to characterize the kinetics and thermodynamics of DNA lesion recognition and base excision
Authors: Minetti Conceição A. S. A. , Remeta David P. , Breslauer Kenneth J.
Published: January 2008

We report a continuous hyperchromicity assay (CHA) for monitoring and characterizing enzyme activities associated with DNA processing. We use this assay to determine kinetic and thermodynamic parameters for a repair enzyme that targets nucleic acid substrates containing a specific base lesion. This optically based kinetics assay exploits the free-energy differences between a lesion-containing DNA duplex substrate and the enzyme-catalyzed, lesion-excised product, which contains at least one hydrolyzed phosphodiester bond. We apply the assay to the bifunctional formamidopyrimidine glycosylase (Fpg) repair enzyme (E) that recognizes an 8-oxodG lesion within a 13-mer duplex substrate (S). Base excision/elimination yields a gapped duplex product (P) that dissociates to produce the diagnostic hyperchromicity signal. Analysis of the kinetic data at 25°C yields a
K
m
of 46.6 nM for the E·S interaction, and a
k
cat
of 1.65 min
−1
for conversion of the ES complex into P. The temperature dependence reveals a free energy (Δ
G
b
) of −10.0 kcal·mol
−1
for the binding step (E + S ↔ ES) that is enthalpy-driven (Δ
H
b
= −16.4 kcal·mol
−1
). The activation barrier (Δ
G
‡
) of 19.6 kcal·mol
−1
for the chemical step (ES ↔ P) also is enthalpic in nature (Δ
H
‡
= 19.2 kcal·mol
−1
). Formation of the transition state complex from the reactants (E + S ↔ ES
‡
), a pathway that reflects Fpg catalytic specificity (
k
cat
/
K
m
) toward excision of the 8-oxodG lesion, exhibits an overall activation free energy (Δ
G
T
‡
) of 9.6 kcal·mol
−1
. These parameters characterize the driving forces that dictate Fpg enzyme efficiency and specificity and elucidate the energy landscape for lesion recognition and repair.