bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐finite‐difference algorithm for integrating Newton's motion equations
Authors: Brzostowski B. , Dudek M. R. , Grabiec B. , Nadzieja T.
Published: January 2007

We have presented some practical consequences on the molecular‐dynamics simulations arising from the numerical algorithm published recently in paper [1]. The algorithm is not a finite‐difference method and therefore it could be complementary to the traditional numerical integrating of the motion equations. It consists of two steps. First, an analytic form of polynomials in some formal parameter λ (we put λ = 1 after all) is derived, which approximate the solution of the system of differential equations under consideration. Next, the numerical values of the derived polynomials in the interval, in which the difference between them and their truncated part of smaller degree does not exceed a given accuracy ε become the numerical solution. The particular examples, which we have considered, represent the forced linear and nonlinear oscillator and the 2D Lennard–Jones fluid. In the latter case we have restricted to the polynomials of the first degree in formal parameter λ.

The computer simulations play very important role in modeling materials with unusual properties being contradictictory to our intuition. The particular example could be the auxetic materials. In this case, the accuracy of the applied numerical algorithms as well as various side‐effects, which might change the physical reality, could become important for the properties of the simulated material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On simultaneous positive and negative Poisson's ratio laminates
Authors: Lim Teik‐Cheng
Published: January 2007

Studies on the mechanical behavior of materials are often performed on the assumption of positive Poisson's ratio except for auxetic materials. Auxetic materials and structures are intriguing systems that exhibit negative Poisson's ratio. Recently some investigation were made on semi‐auxetic materials in terms of their directional and positional auxeticity. In this paper we furnish a simple example of a 3‐ply laminate consisting of isotropic plies whereby the sign of its effective Poisson's ratio changes when the loading mode changes between pure axial loading and pure bending. In addition, both positive and negative Poisson ratio behaviors do not cancel one another, but are simultaneously manifested when the above‐mentioned loading modes are combined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
QSPR Modeling of Heats of Combustion for Carboxylic Acids
Authors: Duchowicz Pablo R. , Garro Juan C. M. , Andrada Matías F. , Castro Eduardo A. , Fernández Francisco M.
Published: January 2007

In the present study, the predictions for heats of combustion achieved with a modified Kharash model are compared with results obtained from the QSPR theory. The homogeneous set of carboxylic acids investigated comprises 52 compounds, and a pool of 1202 theoretically defined molecular descriptors provided by the software Dragon 5 are explored using both the Forward Stepwise Regression technique and the new proposed Replacement Method procedure. Final results suggest that the linear regression analyses employed are not able to lead to a better quality model.
In Silico ADME Modeling 3: Computational Models to Predict Human Intestinal Absorption Using Sphere Exclusion and kNN QSAR Methods
Authors: Gunturi Sitarama B. , Narayanan Ramamurthi
Published: January 2007

Modeling of human intestinal absorption (HIA) data of 175 diverse drugs and 336 calculated descriptors is performed to develop global predictive models that are applicable to the whole medicinal chemistry space. With this aim, we employed two automated procedures, (a) Sphere Exclusion Algorithm (SEA) to select members of the training and test sets based on structural dissimilarity and (b) k‐Nearest Neighbors (kNN) method along with Genetic Algorithms (kNN‐QSAR‐GA) to select significant and independent descriptors. This methodology helped us to derive optimal Quantitative Structure–Property Relationship (QSPR) models based on three and four descriptors. The best three descriptor model is based on Delta Chi Index of order 3 (Cluster), Hydrogen type E‐State index ShsOH, AlogP99 ($\rm{ q_{{\rm{LOO}}}^2 }$=0.7401 and $\rm{ q_{{\rm{ext}}}^2 }$=0.7989); the best four variable model is based on auto‐correlation descriptor (Moran) weighted by atomic weights – order 7, AI‐State_Indices_AISssssC, number of hydrogen bond acceptors, AlogP99 ($\rm{ q_{{\rm{LOO}}}^2 }$=0.8196 and $\rm{ q_{{\rm{ext}}}^2 }$=0.6999). Based on extensive validation tests of the models M1–M4, comparison of their overall performance and $\rm{ q_{{\rm{ext}}}^2 }$ statistics with reported models using other approaches, it is shown that: (a) the models have high stability and are robust and (b) for the first time in HIA modeling, the combination of an automated training set selection (SEA) followed by variable selection (kNN‐QSAR_GA) is shown to be a promising methodology to build multiple stable models that are useful in consensus prediction. From the analysis of the physical meaning of the selected descriptors, it is inferred that the HIA of small organic compounds can be accurately predicted using calculated descriptors that code for the following fundamental properties: (1) lipophilicity, (2) hydrogen bonding capacity, (3) size, and (4) shape and further, the role of new calculated descriptors on the HIA profile of small organic compounds is uncovered. Finally, as the models reported herein are based on computed properties, they appear to be a valuable tool in virtual screening, where selection and prioritization of candidates is required.
NO migration from N‐methyl‐N‐nitrosobenzene‐sulfonamide to 3,6‐dibromocarbazole: Concerted or stepwise reaction path?
Authors: Zhang Dongju , Sun Hui , Wang Fang , Liu Chengbu
Published: January 2007

The NO migration from N‐methyl‐N‐nitrosobenzene‐sulfonamide to 3,6‐dibromocarbazole was proposed in a recent literature to follow a stepwise reaction path. However, the present density functional theory calculations at the MP2/6–31G(d,p)//B3LYP/6–31G(d,p) level show that this reaction exclusively proceeds via a concerted mechanism involving a four‐membered ring transition state. The calculated barrier is in good agreement with the experimental finding. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
A repeated measures concordance correlation coefficient
Authors: King Tonya S. , Chinchilli Vernon M. , Carrasco Josep L.
Published: January 2007

The concordance correlation coefficient is commonly used to assess agreement between two raters or two methods of measuring a response when the data are measured on a continuous scale. However, the situation may arise in which repeated measurements are taken for each rater or method, e.g. longitudinal studies in clinical trials or bioassay data with subsamples. This paper proposes a coefficient for measuring agreement between two raters or two methods of measuring a response in the presence of repeated measurements. We illustrate the methodology with examples comparing (1) 1‐hr versus 2‐hr blood draws for measuring cortisol in an asthma clinical trial and (2) two measurements of percentage body fat, from skinfold calipers and dual energy X‐ray absorptiometry. Copyright © 2007 John Wiley & Sons, Ltd.
Experimental investigation on weather cues for mast seeding of Fagus crenata
Authors: Kon Hirokazu , Noda Takashi
Published: January 2007

Although a recent study has suggested that the minimum temperature from late April to mid‐May in the year preceding flowering causes mast seeding in Fagus crenata, no direct evidence is available to support this finding. The aim of the present investigation was, therefore, to test – in a field experiment – whether the minimum temperature determines mast seeding in F. crenata. We examined the effect of nighttime temperatures on flower‐bud initiation in F. crenata by enclosing fruit‐bearing branches in heated bags at night, thereby maintaining average nighttime temperatures of approximately 2°C above the ambient temperatures. Heating was applied at night from 21 April to 20 May, 21 May to 19 June, and 21 April to 19 June in 2001. Female inflorescence initiation was inhibited by the nocturnal heating in the period 21 April to 20 May and 21 May to 19 June. However, nocturnal heating from 21 April to 20 May was the more important based on the odds ratio of the former being much lower than that of the latter in a logistic regression model. Male inflorescence initiation was also inhibited by nocturnal heating from 21 April to 20 May. We therefore conclude that flower‐bud initiation in F. crenata was controlled by nighttime temperatures between 21 April and 20 May.
Prevalence of ECG abnormalities in an international survey of patients with suspected or confirmed heart failure at death or discharge
Authors: Khan Nasrin K. , Goode Kevin M. , Cleland John G.F. , Rigby Alan S. , Freemantle Nick , Eastaugh Joanne , Clark Andrew L. , de Silva Ramesh , Calvert Melanie J. , Swedberg Karl , Komajda Michael , Mareev VIu , Follath Ferenc ,   EuroHeart Failure Survey Investigators
Published: January 2007

Background

Most patients suspected of having heart failure (HF) will get a 12‐lead electrocardiogram (ECG) but its utility for excluding HF or assisting in its management has rarely been investigated.

Methods

The EuroHeart Failure survey identified 11,327 patients hospitalised with a suspected diagnosis of HF from 115 hospitals in 24 countries. ECGs were obtained from 9315 patients, of whom 5934 had cardiac imaging tests. The utility of the ECG was assessed for excluding or diagnosing major structural heart disease (MSHD) or major left ventricular systolic dysfunction (MLVSD) and for therapeutic decision making.

Findings

MSHD was present in 70% and MLVSD in 54% of patients overall but in only 21% and 5%, respectively, if the ECG was entirely normal. However, <2% of patients had a normal ECG. No single ECG characteristic identified a probability <25% of MSHD or <20% of MLVSD. Patients with QRS width ≥120 ms or anterior pathological Q‐waves had a probability >80% of MSHD and >70% of MLVSD. Diagnostic models suggested that electrocardiographic criteria alone were not accurate for the diagnosis or exclusion of important heart disease in this population. However, 2468 patients (42%) had an electrocardiographic finding that should be used to guide the choice of therapy.

Conclusions

A normal ECG is rare in patients with suspected HF but has limited diagnostic value in this setting. The ECG has an important role in guiding therapy.
Health-enhancing physical activity among Saudi adults using the International Physical Activity Questionnaire (IPAQ)
Authors: Al-Hazzaa Hazzaa M
Published: January 2007

Objectives

To describe the physical activity profile of Saudi adults living in Riyadh, using the International Physical Activity Questionnaire (IPAQ) short-version telephone format.

Methods

Physical activity was assessed using the official Arabic short form of IPAQ, intended for use in telephone interview. The instrument asks for times spent in walking, moderate- and vigorous-intensity physical activity of at least 10 min duration. The sample consisted of 1616 Saudis, between 15 and 78 years of age, living in Riyadh. Participants were drawn from a list of names in the telephone book using a simple random method. Telephone interviews were administered during the spring of 2003 by trained male interviewers.

Results

The final sample size was 1064 Saudi males and females (response rate of 66%), with males comprising about 66% of the respondents. Over 43% of Saudis did not participate in any type of moderate-intensity physical activity lasting for at least 10 min. More than 72% of the sample did not engage in any type of vigorous-intensity physical activity lasting for at least 10 min. The proportion of Saudis who walked for 150 min or more per week was 33.3%. Females were engaged more in moderate physical activity than males, whereas males participated more in vigorous activity compared with females. Activity levels did not show significant relationships with education level or job hours per week. Based on the three activity categories established by IPAQ, 40.6% of Saudis were inactive, 34.3% were minimally active and 25.1% were physically active. Physical inactivity increased with advancing age.

Conclusion

The data suggest that the prevalence of physical inactivity among Saudis adults is relatively high. Efforts are needed to encourage Saudis to be more physically active, with the goal of increasing the proportion of Saudis engaging in health-enhancing physical activity.
Impact of parental education and income inequality on children's food intake
Authors: Sausenthaler Stefanie , Kompauer Iris , Mielck Andreas , Borte Michael , Herbarth Olf , Schaaf Beate , von Berg Andrea , Heinrich Joachim ,   for the LISA Study Group
Published: January 2007

Objective

To analyse the association between socio-economic indicators and diet among 2-year-old children, by assessing the independent contribution of parental education and equivalent income to food intake.

Design

The analysis was based on data from a prospective birth cohort study. Information on diet was obtained using a semi-quantitative food-frequency questionnaire. Low and high intake of food was defined according to the lowest and the highest quintile of food consumption frequency, respectively.

Setting

Four German cities (Munich, Leipzig, Wesel, Bad Honnef), 1999–2001.

Subjects

Subjects were 2637 children at the age of 2 years, whose parents completed questionnaires gathering information on lifestyle factors, including parental socio-economic status, household consumption frequencies and children's diet.

Results

Both low parental education and low equivalent income were associated with a low intake of fresh fruit, cooked vegetables and olive oil, and a high intake of canned vegetables or fruit, margarine, mayonnaise and processed salad dressing in children. Children with a low intake of milk and cream, and a high intake of hardened vegetable fat, more likely had parents with lower education. Low butter intake was associated with low equivalent income only.

Conclusions

These findings may be helpful for future intervention programmes with more targeted policies aiming at an improvement of children's diets.
Fruit and vegetable consumption and self-reported functional health in men and women in the European Prospective Investigation into Cancer–Norfolk (EPIC–Norfolk): a population-based cross-sectional study
Authors: Myint Phyo K , Welch Ailsa A , Bingham Sheila A , Surtees Paul G , Wainwright Nicholas WJ , Luben Robert N , Wareham Nicholas J , Smith Richard D , Harvey Ian M , Day Nicholas E , Khaw Kay-Tee
Published: January 2007

Objectives

To investigate the association between fruit and vegetable consumption and self-reported physical and mental functional health measured by an anglicised short-form 36-item questionnaire (UK SF-36).

Design

Population-based cross-sectional study.

Setting

General community in Norfolk, UK.

Subjects

A total of 16 792 men and women aged 40–79 years recruited from general practice population registers as part of the European Prospective Investigation into Cancer (EPIC)–Norfolk study, who completed food-frequency questionnaires in 1993–1997 and Health and Life Experiences Questionnaires 18 months later, were enrolled in the study.

Results

Mean SF-36 physical component summary scores increased significantly with increasing total fruit and vegetable consumption in both men and women (P <  0.0001 for trend). Men and women in the top quartile of consumption compared with the bottom quartile had a significantly higher likelihood of reporting good physical health (defined as a score ≥ 55); odds ratio (OR) 1.30, 95% confidence interval (CI) 1.11–1.53 for men and OR 1.28, 95% CI 1.11–1.48 for women, after controlling for age, body mass index, smoking, education, social class, prevalent illness and total energy intake. Exclusion of current smokers and people with prevalent illness did not alter the associations.

Conclusion

Higher fruit and vegetable consumption is associated with better self-reported physical functional health within a general population. Increasing daily intake by two portions of fruit and vegetables was associated with an 11% higher likelihood of good functional health. Since the current average consumption of fruit and vegetables in the UK is about three portions, the recommended ‘five a day’ strategy may have additional benefit for functional as well as other health outcomes in the population.
Tremor
Authors: Raethjen  , Deuschl
Published: January 2007

Tremor ist eines der häufigsten neurologischen Symptome. Die genaue Diagnose wird in der Regel klinisch gestellt. Der häufigste primär neurologisch bedingte Tremor ist der Essentielle Tremor (Prävalenz 2–5%), der sich überwiegend als relativ symmetrischer Halte- und kinetischer Tremor zeigt. Er folgt in 60% der Fälle einem autosomal dominanten Erbgang, bessert sich bei 60–70% der Patienten unter Alkohol und kann außer den Händen den Kopf und die Stimme betreffen. Der Parkinson-Tremor tritt dagegen überwiegend in Ruhe auf und beginnt asymmetrisch, häufig unter Beteiligung von Beinen und Gesicht. Der cerebelläre Tremor ist ein Intentionstremor. Der hochfrequente Orthostatische Tremor betrifft hauptsächlich die Beine und führt zu einer Standunsicherheit. Der Dystone Tremor ist ein Aktionstremor der betroffenen Körperregion. Die symptomatische medikamentöse Therapie des Tremors wird in erster Linie von der klinischen Erscheinungsform bestimmt. Während Halte- und Aktionstremores hauptsächlich auf nicht-selektive Betablocker (Propranolol), Primidon, manche neuere Antiepileptika (Gabapentin, Topiramat) und Benzodiazepine ansprechen, bessern sich klassische Ruhetremores unter dopaminergen Substanzen (Levodopa, Dopaminagonisten) oder Anticholinergika. Beim Dystonen Tremor sind häufig Botulinum-Toxin Injektionen erfolgreich, der orthostatische Tremor spricht bei einem Teil der Patienten auf Gabapentin oder Benzodiazepine an. Für medikamentös therapierefraktäre, schwer behinderte Patienten besteht bei der Mehrzahl der Tremores die Möglichkeit der Implantation von Stimulationselektroden in den VIM-Kern des Thalamus mit sehr guten Erfolgen aber vorhandenen Risiken.
Dystonien – Botulinumtoxin, tiefe Hirnstimulation, Medikamente, motorisches Training
Authors: Ceballos-Baumann
Published: January 2007

Trotz erheblicher Fortschritte in dem Verständnis der Dystonien auf genetischer und systemphysiologischer Ebene bleibt die Therapie der meisten Formen der Dystonien rein symptomatisch. Botulinumneurotoxin (BoNT) ist das Mittel der ersten Wahl für fokale Dystonie. Ausgewählte Problemstellungen der BoNT-Therapie bei Dystonien im kraniozervikalen Bereich werden illustriert. Bei bestimmten fokalen, insbesondere bei generalisierten Dystonien ist BoNT nicht ausreichend oder nicht indiziert. Hier stehen nach wie vor Anticholinergika und andere Medikamente, in zunehmenden Maße die tiefe Hirnstimulation sowie physio- und ergotherapeutische Methoden zur Verfügung. Erfahrungen zu etablierten Vorgehensweisen und neue Entwicklungen in der Dystonie-Therapie werden in der Übersicht diskutiert.
Differenzialdiagnose des Morbus Parkinson
Authors: Ludin
Published: January 2007

Die Diagnose des Morbus Parkinson galt bis vor wenigen Jahren als einfach. Die zunehmenden therapeutischen Möglichkeiten haben in den letzten Jahren aber gezeigt, dass sowohl in therapeutischer als auch in prognostischer Hinsicht die Abgrenzung von einer Reihe von Krankheitsbildern, die in der Folge skizziert werden, wichtig ist.
Morbus Whipple
Authors: Marth
Published: January 2007

Der Morbus Whipple ist eine chronische Infektionskrankheit, die meist bei Männern mittleren Alters auftritt und oft schleichend über Jahre verläuft. Der Erreger, Tropheryma whipplei, ist inzwischen phylogenetisch definiert und angezüchtet worden. Trotz der weiten Verbreitung dieses Erregers in der Umwelt ist die Erkrankung selten. Diese Diskrepanz ist wahrscheinlich mit zellulären Immundefekten erklärbar. Das klinische Bild des Morbus Whipple ist oft variabel und daher wird die Diagnose mittels Duodenalbiopsie oft erst nach langer Verzögerung gestellt. Die antibiotische Therapie führt oft zur Krankheitsremission. Dennoch gibt es eine Reihe von Patienten, die auf die Therapie nicht oder nicht ausreichend ansprechen oder gefährliche Rezidive erleiden.
Probabilities for jumping fault segment stepovers
Authors: Shaw Bruce E. , Dieterich James H.
Published: January 2007

Seismic hazard analysis relies heavily on the segmentation of faults. The ability of ruptures to break multiple segments has a big impact on estimated hazard. Current practice for estimating multiple segment breakage relies on panels of experts voting on their opinions for each case. Here, we explore the probability of elastodynamic ruptures jumping segment stepovers in numerical simulations of segmented fault systems. We find a simple functional form for the probability of jumping a segment stepover as a function of stepover distance: an exponential falloff with distance. We suggest this simple parameterization of jumping probabilities, combined with sparse observational data to fix the lengthscale parameter, as a new approach to estimating multisegment earthquake hazard.
Typhoon‐induced, highly nonlinear internal solitary waves off the east coast of Korea
Authors: Nam SungHyun , Kim Duk‐jin , Kim Hyoung Rok , Kim Young‐Gyu
Published: January 2007

Highly nonlinear internal solitary waves (ISWs) propagating both onshore and offshore were detected in a SAR image taken approximately 19 hours after typhoon MAEMI's passage across the east coast of Korea. Analysis of ocean buoy data suggests that the ISWs were generated by near‐inertial waves in response to typhoon wind. The near‐inertial waves can propagate seaward due to a downwelling coastal jet (positive relative vorticity offshore of the jet), and interact with sharply varying topography, producing the ISWs. The area of sharply varying topography approximately 28 km off the coast is suggested as a source region for the ISWs. Simple calculations of wave speed based on the two‐layered Korteweg‐deVries (KdV) equation with upper layer thickness and densities at both layers fixed indicate that the ISWs were generated 6 hours prior to the time of the acquisition of the SAR image (approximately 13 hours after the typhoon passage), consistent with simultaneous buoy measurements.
Comparative statistical analysis of storm time activations and sawtooth events
Authors: Pulkkinen T. I. , Partamies N. , McPherron R. L. , Henderson M. , Reeves G. D. , Thomsen M. F. , Singer H. J.
Published: January 2007

Statistical properties of storm time magnetospheric activity are examined using superposed epoch analysis. We show that about half of storm time auroral electrojet activations have signatures that are typical of nonstorm substorms, including geostationary orbit injections and magnetic field dipolarizations. Analysis of a separate data set of sawtooth events shows that they have auroral and inner magnetosphere characteristics that are quite similar to those found generally during storm time activity. Hence it is concluded that the sawtooth events do not represent a specific class of magnetospheric activity. Examination of the solar wind and IMF properties showed that about 30% of storm time substorm‐like activations and about 20% of the sawtooth oscillations have associated solar wind or IMF triggers and that triggering is more likely during high solar wind pressure and fluctuating IMF. The solar wind‐magnetosphere coupling efficiency is shown to be independent of the solar wind Mach number or level of IMF fluctuations but dependent on the level of driving; when EY is small, the ionospheric dissipation, ring current intensification, and geostationary field stretching are relatively larger than when the driving EY is large.
Effects of overlying velocity on periphyton structure and denitrification
Authors: Arnon Shai , Packman Aaron I. , Peterson Christopher G. , Gray Kimberly A.
Published: January 2007

The effects of overlying flow conditions on periphyton structure and denitrification were measured in three laboratory mesocosms (120 cm long and 60 cm wide) under average velocities of 0.05, 0.5 and 5 cm/s. Periphyton was cultivated on polyethylene benthic nets overlaying a thin layer of sand. The mesocosms were operated continuously for four months, leading to prolific growth of periphyton on the benthic nets and in the underlying sediments. Periphyton structural characteristics were quantified in terms of algal/bacterial biomass, algal species composition, and microbial enumeration. Confocal microscopy was used to investigate the spatial organization of the periphyton. The denitrification potential of the microbial community in each mesocosm was evaluated using the acetylene inhibition method. Different benthic microbial communities developed under the three flow conditions, while the total microbial biomass accrual increased monotonically with increasing overlying velocity. Denitrification potential also increased with overlying velocity when evaluated on both a per unit area and per unit biomass basis. The periphytic community that developed under the fastest velocity and was characterized by the largest fractional biovolume of diatoms (predominantly Achnanthidium minutissimum), promoted establishment of a consortium of bacterial denitrifiers more physiologically active than those that developed under slower overlying velocities. These results demonstrate that hydrodynamic transport conditions play a key role in structuring benthic microbial communities, and the structural differences that develop under different flow conditions also regulate benthic microbial processing of substances delivered from the water column. Understanding the response of microbial communities to physical conditions is essential for evaluating nutrients dynamics, as well as for the development of management strategies aimed at mitigating effects of excess nitrogen by increasing denitrification in shallow aquatic systems.
Endolithic aspartic acid as a proxy of fluctuations in coral growth
Authors: Gupta Lallan P. , Suzuki Atsushi , Kawahata Hodaka
Published: January 2007

Coral skeleton has been widely studied for monitoring past fluctuations in marine environment. Although stable carbon isotope (δ13C) data appear to reflect coral metabolism, their interpretations differ from place to place and are sometimes controversial, because they are also affected by carbon isotopic composition of dissolved inorganic carbon in seawater. Association of an organic matrix with biological carbonates has been reported in many previous studies. With the help of high‐resolution microsampling of coral skeleton and advanced technique for amino acid (AA) quantification in low‐volume sample, we show that aspartic acid (Asp) in coral skeleton varies with distinct seasonal pattern, and is useful in understanding why corals calcify faster in summer than in winter. Since Asp containing organic matrix in the skeleton is synthesized by the coral, changes in mole concentration of Asp relative to other AAs of the skeleton make it a potential indicator for monitoring fluctuations in coral physiology in the past.
Spatial Specificity of BOLD versus Cerebral Blood Volume fMRI for Mapping Cortical Organization
Authors: Smirnakis Stelios M , Schmid Michael C , Weber Bruno , Tolias Andreas S , Augath Mark , Logothetis Nikos K
Published: January 2007

Intravascular contrast agents are used in functional magnetic resonance imaging to obtain cerebral blood volume (CBV) maps of cortical activity. Cerebral blood volume imaging with MION (monocrystalline-iron-oxide-nanoparticles) increases the sensitivity of functional imaging compared with the blood oxygenation level-dependent (BOLD) signal ( Leite et al, 2002 ; Mandeville et al, 1998 ; Vanduffel et al, 2001 ). It therefore represents an attractive method for obtaining detailed maps of cortical organization ( Vanduffel et al, 2001 ; Zhao et al, 2005 ). However, it remains to be determined how the spatial profile of CBV maps of cortical activity derived with MION compares with the profile of BOLD activation maps under a variety of different stimulation conditions. We used several stimulation paradigms to compare the spatial specificity of CBV versus BOLD activation maps in macaque area V1 at 4.7 T. We observed that: (1) CBV modulation is relatively stronger in deep cortical layers compared with BOLD, in agreement with studies in cats ( Harel et al, 2006 ) and rodents ( Lu et al, 2004 ; Mandeville and Marota, 1999 ) and (2) surprisingly, under large surround stimulation conditions, CBV maps extend along the cortical surface to cover large (>10 mm) regions of the cortex that are devoid of significant BOLD modulation. We conclude that the spatial profiles of BOLD and CBV activity maps do not coregister across all stimulus conditions, and therefore do not necessarily represent equivalent transforms of the neural response. Cerebral blood volume maps should be interpreted with care, in the context of the particular experimental paradigm applied.
Contribution of Poly(ADP-Ribose) Polymerase to Postischemic Blood—Brain Barrier Damage in Rats
Authors: Lenzsér Gábor , Kis Béla , Snipes James A , Gáspár Tamás , Sándor Péter , Komjáti Katalin , Szabó Csaba , Busija David W
Published: January 2007

The nuclear enzyme poly(ADP-ribose) polymerase (PARP) is activated by oxidative stress and plays a significant role in postischemic brain injury. We assessed the contribution of PARP activation to the blood–brain barrier (BBB) disruption and edema formation after ischemia–reperfusion. In male Wistar rats, global cerebral ischemia was achieved by occluding the carotid arteries and lowering arterial blood pressure for 20 mins. The animals were treated with saline or with the PARP inhibitor N-(6-oxo-5,6-dihydrophenanthridin-2-yl)- N, N-dimethylacetamide.HCl (PJ34); (10 mg/kg, i.v.) before ischemia. After 40 mins, 24, and 48 h of reperfusion, the permeability of the cortical BBB was determined after Evans Blue (EB) and Na-fluorescein (NaF) administration. The water content of the brain was also measured. The permeability of the BBB for EB increased after ischemia–reperfusion compared with the nonischemic animals after 24 and 48 h reperfusion but PARP inhibition attenuated this increase at 48 h (nonischemic: 170 ± 9, saline: 760 ± 95, PJ34: 472 ± 61 ng/mg tissue). The extravasation of NaF showed similar changes and PJ34 post-treatment attenuated the permeability increase even at 24 h. PARP inhibition decreased the brain edema seen at 48 h. Because PARP has proinflammatory properties, the neutrophil infiltration of the cortex was determined, which showed lower values after PJ34 treatment. Furthermore, PJ34 treatment decreased the loss of the tight junction protein occludin at 24 and 48 h. The inhibition of PARP activity accompanied by reduced post-ischemic BBB disturbance and decreased edema formation suggests a significant role of this enzyme in the development of cerebral vascular malfunction.
Ultraviolet writing of channel waveguides in proton-exchanged LiNbO3
Authors: Gallo Katia , Gawith Corin B. E. , Wellington Iain T. , Mailis Sakellaris , Eason Robert W. , Smith Peter G. R. , Richardson David J. , Kostritskii Sergey M.
Published: January 2007

We report on a direct ultraviolet (UV) writing method for the fabrication of channel waveguides at 1.55μm in LiNbO3 through UV irradiation of surface and buried planar waveguides made by annealed proton exchange and reverse proton exchange. A systematic study of the guidance properties as a function of the UV writing conditions is presented.
Water-assisted synthesis of silicon oxide nanowires under supercritically hydrothermal conditions
Authors: Lin L. W. , Tang Y. H. , Li X. X. , Pei L. Z. , Zhang Y. , Guo C.
Published: January 2007

Large-scale amorphous silicon oxide nanowires (SiONWs) have been synthesized from silicon monoxide powder under supercritically hydrothermal conditions. The chemical bonding of amorphous SiONWs were investigated with Fourier-transform infrared (FTIR) spectrometry and near-edge x-ray absorption fine structure (NEXAFS) spectrometry. Our results show that the SiONWs are tens of microns long with a diameter from tens to hundreds of nanometers. Selected area electron diffraction (SAED) shows that the samples are amorphous. Energy dispersive x-ray spectrometry (EDX) analysis reveals that the SiONWs consist of Si and O elements in an atomic ratio approximately equal to 1:1.5. The results of FTIR and NEXAFS indicate that some OH groups are located on the surface of the SiONWs in the form of Si–OH. The relation between the chemical bonding and the possible growth mechanism was also discussed. During the growth process, water is an important species, which can provide H+ and OH− under supercritically hydrothermal conditions. The H+ and OH− block the defects of Si–O• and Si•, respectively, in the form of Si–OH and stabilize the structure. The Si–OH can reduce the adsorption activity of the SiONW surface which may be in favor of preventing the growth from the cross section and assisting the growth along the axial direction of the SiONWs.
Numerical designing of semiconductor structure for optothermionic refrigeration
Authors: Han Peng , Jin Kui-juan , Zhou Yue-Liang , Lu Hui-Bin , Yang Guo-Zhen
Published: January 2007

The cooling processes in the system of AlxIn1−xAs∕InP∕AlxIn1−xAs are analyzed with a self-consistent calculation based on the model of optothermionic refrigeration. The refrigeration heat as several W∕cm2 is obtained theoretically with the optimal parameters of the aluminum atom fraction x and the doping density for the system. Due to the small Auger coefficient and the lower carriers’ density in the InP well, the Auger dissipation heat in the present system is smaller than that in the system of AlGaAs∕GaAs∕AlGaAs. Furthermore, the applied bias range for obtaining high cooling heat in the present system is calculated to be larger than that in the system of GaAs. For obtaining larger cooling heat, a double-well system of AlxIn1−xAs∕InP∕AlxIn1−xAs∕InP∕AlxIn1−xAs is designed, in which the maximum cooling heat is predicted as about 50% higher than that in a single-well system of AlxIn1−xAs∕InP∕AlxIn1−xAs.
Polarity and piezoelectric response of solution grown zinc oxide nanocrystals on silver
Authors: Scrymgeour David A. , Sounart Thomas L. , Simmons Neil C. , Hsu Julia W. P.
Published: January 2007

The crystal orientation and piezoelectric properties of solution grown ZnO nanorods on Ag films were measured by quantitative piezoelectric force microscopy (PFM). The polarity of the rods, important for many device applications, was determined to be oriented [0001] from the substrates. This indicates that the prevalence of the [0001] oriented crystals is dominated by the fastest growing direction in solution. The average value of the d33 piezoelectric coefficient was measured to be 4.41pm∕V, with a standard deviation of 1.73pm∕V among the 198 individual rods. For calibration and comparison, PFM measurements were also performed on single crystals of x-cut quartz, z-cut periodically poled and single domain LiNbO3, and z-cut ZnO. Repeated measurements on individual rods establish that the run-to-run variation of a single rod is similar to that of single crystal measurements on quartz and LiNbO3. Hence, the observed rod-to-rod variation is not due to measurement uncertainty. Potential origins of this rod-to-rod difference will be discussed.
Effects of surface stresses on contact problems at nanoscale
Authors: Wang G. F. , Feng X. Q.
Published: January 2007

Based on the surface elasticity theory, we examined the effects of surface stresses on nanosized contact problems. The Fourier integral transform method is adopted to derive the general solution for the contact problem under pressure. As two examples, the deformations induced, respectively, by a uniform distributed pressure and a concentrated force are analyzed in detail. The results indicate some interesting characteristics in contact mechanics, which are distinctly different from those in classical elasticity theory. Both the contact normal stress and the deformation gradient on the deformed surface vary smoothly across the loading boundary as a result of surface stress. In addition, the indent depth and the maximum normal contact stress depend strongly on the surface stress for nanoindentation.
Prediction of MAX phases, VN+1SiCN (N=1,2), from first-principles theory
Authors: Fang C. M. , Ahuja R. , Eriksson O.
Published: January 2007

We have investigated the phase stability of two MAX phases, V3SiC2 and V2SiC, by means of first-principles total-energy calculations within the generalized-gradient approximation and the projector-augmented wave method. The theoretical bulk modulus of V3SiC2 is 219GPa, which is ∼17% larger than that of Ti3SiC2 (187GPa). The total-energy calculations show that V2SiC is stable with a formation energy of about 0.27eV̸f.u. and that V3SiC2 is metastable (only 0.02eV̸f.u. is required to stabilize this phase from its competing phases). We suggest that both these two MAX compounds should be possible to synthesize as stable (or metastable) phases using, e.g., thin-film deposition.
Tunnel magnetoresistance and Coulomb blockade in a planar assembly of cobalt nanoclusters embedded in TiO2
Authors: Varalda J. , Ortiz W. A. , de Oliveira A. J. A. , Vodungbo B. , Zheng Y.-L. , Demaille D. , Marangolo M. , Mosca D. H.
Published: January 2007

Magnetic and magnetotransport properties of Co nanoclusters embedded in a TiO2 matrix grown by pulsed laser deposition have been studied. The results show a tunneling magnetoresistance associated with spin-polarized multiple quantum tunneling through the Coulomb energy barrier (Coulomb blockade effect). A shift between the fields at the magnetoresistance maxima and the coercive fields in the Coulomb blockade regime is observed. This shift decreases with increasing temperature and disappears when the thermal energy becomes stronger than the Coulomb blockade energy.
Gain in p-doped quantum dot lasers
Authors: Smowton P. M. , Sandall I. C. , Liu H. Y. , Hopkinson M.
Published: January 2007

We directly measure the gain and threshold characteristics of three quantum dot laser structures that are identical except for the level of modulation doping. The maximum modal gain increases at fixed quasi-Fermi level separation as the nominal number of acceptors increases from 0 to 15 to 50 per dot. These results are consistent with a simple model where the available electrons and holes are distributed over the dot, wetting layer, and quantum well states according to Fermi-Dirac statistics. The nonradiative recombination rate at fixed quasi-Fermi level separation is also higher for the p-doped samples leading to little increase in the gain that can be achieved at a fixed current density. However, we demonstrate that in other similar samples, where the difference in the measured nonradiative recombination is less pronounced, p doping can lead to a higher modal gain at a fixed current density.
Optical properties of isolated cobalt clusters synthesized by ion implantation
Authors: Gilliot M. , En Naciri A. , Johann L. , Stoquert J. P. , Grob J. J. , Muller D.
Published: January 2007

Optical properties of nanostructured cobalt-implanted silica thin films have been investigated in the 350–850nm spectral range using rotating polarizer spectroscopic ellipsometer. SiO2 thin layers on Si substrates have been implanted with Co+ ions at energy of 160keV and at fluences of 1017ions∕cm2 for different temperatures of substrate during implantation (77, 295, and 873K). The formation of isolated cobalt clusters is clearly observed using transmission electron microscope. The optical responses of the implanted layers are analyzed by comparing the ellipsometric experimental data to different models including interference effects and metal inclusions effects into the dielectric layer. The simulated ellipsometric data are obtained by calculating the interferometric optical response of an inhomogeneous layer on a Si substrate. The material within this layer is considered as an effective medium, which dielectric function is calculated using the Maxwell-Garnett (MG) effective medium approximation. The possibilities of ellipsometry for the study of the optical properties of such clusters-embedded films, the size effects, and the applicability of the MG approach are also discussed. We show that although the structures of these layers are very complicated because of ion implantation mechanisms, quite simple models based on three layer structures can provide good agreement. We especially provide the evidence that ellipsometry can give interesting information about the optical properties of nanostructured layers. This is of special interest in the field of nanostructured layered systems, where ellipsometry appears to be a suitable optical characterization technique.
Vanadium donor and acceptor levels in semi-insulating 4H- and 6H-SiC
Authors: Mitchel W. C. , Mitchell W. D. , Landis G. , Smith H. E. , Lee Wonwoo , Zvanut M. E.
Published: January 2007

The electronic levels of vanadium in semi-insulating 4H- and 6H-SiC have been reinvestigated using temperature dependent Hall effect and resistivity measurements at temperatures up to 1000K in conjunction with electron paramagnetic resonance (EPR) and optical absorption measurements which were used to identify the charge state of vanadium in the material. Two distinct thermal activation energies were found for each polytype. The shallower of the two levels correlated with the presence of both V3+ and V4+ in the EPR and absorption experiments, demonstrating that this level is the vanadium acceptor level while the deeper level is the donor level for which the V4+ charge state was observed. The results for the V4+∕5+ donor level, EC−1.57±0.09eV for 4H-SiC and EC−1.54±0.06eV for 6H-SiC, are in agreement with the generally accepted values. However, the results for the V3+∕4+ acceptor level, EC−0.85±0.03eV in 6H-SiC and EC−1.11±0.08eV in 4H-SiC, are significantly higher than previously assumed. Variations in crystal quality and purity may explain the differences in the previously reported values for the donor and acceptor levels.
Coarse-grained protein molecular dynamics simulations
Authors: Derreumaux Philippe , Mousseau Normand
Published: January 2007

A limiting factor in biological science is the time-scale gap between experimental and computational trajectories. At this point, all-atom explicit solvent molecular dynamics (MD) are clearly too expensive to explore long-range protein motions and extract accurate thermodynamics of proteins in isolated or multimeric forms. To reach the appropriate time scale, we must then resort to coarse graining. Here we couple the coarse-grained OPEP model, which has already been used with activated methods, to MD simulations. Two test cases are studied: the stability of three proteins around their experimental structures and the aggregation mechanisms of the Alzheimer’s Aβ16–22 peptides. We find that coarse-grained isolated proteins are stable at room temperature within 50ns time scale. Based on two 220ns trajectories starting from disordered chains, we find that four Aβ16–22 peptides can form a three-stranded β sheet. We also demonstrate that the reptation move of one chain over the others, first observed using the activation-relaxation technique, is a kinetically important mechanism during aggregation. These results show that MD-OPEP is a particularly appropriate tool to study qualitatively the dynamics of long biological processes and the thermodynamics of molecular assemblies.
Ab initio molecular dynamics study of manganese porphine hydration and interaction with nitric oxide
Authors: Leung Kevin , Medforth Craig J.
Published: January 2007

The authors use ab initio molecular dynamics and the density functional theory+U (DFT+U) method to compute the hydration environment of the manganese ion in manganese (II) and manganese (III) porphines (MnP) dispersed in liquid water. These are intended as simple models for more complex water soluble porphyrins, which have important physiological and electrochemical applications. The manganese ion in Mn(II)P exhibits significant out-of-porphine plane displacement and binds strongly to a single H2O molecule in liquid water. The Mn in Mn(III)P is on average coplanar with the porphine plane and forms a stable complex with two H2O molecules. The residence times of these water molecules exceed 15ps. The DFT+U method correctly predicts that water displaces NO from Mn(III)P–NO, but yields an ambiguous spin state for the MnP(II)–NO complex.
Integral relations for the interfacial heat and mass transfer resistivities and the inverted temperature gradient
Authors: Johannessen Eivind , Bedeaux Dick
Published: January 2007

The occurrence of an inverted temperature gradient in a vapor between two liquids kept at different temperatures was first predicted by Pao [Phys. Fluids 14, 306 (1971)] using kinetic theory. Using integral relations for the interfacial heat and mass transfer resistivities derived in an earlier paper, we show the general validity of a criterion for the occurrence of an inverted temperature gradient for a one-component fluid in the slow evaporation/condensation regime. This criterion was first derived by Pao and subsequently rederived in an equivalent form using nonequilibrium thermodynamics. The general validity of this criterion means that there will always be an inverted temperature gradient in the vapor between a hot and cold liquid. We present numerical solutions of the nonequilibrium van der Waals square gradient model which agree with this general result. The numerical results also show the effects of the magnitude of the evaporation/condensation flux and the excess resistivity in the interfaces. We only consider fluxes and gradients in the direction normal to the interfaces, so the system is in essence one-dimensional.
Hydrogen passivation of nitrogen in GaNAs and GaNP alloys: How many H atoms are required for each N atom?
Authors: Buyanova I. A. , Chen W. M. , Izadifard M. , Pearton S. J. , Bihler C. , Brandt M. S. , Hong Y. G. , Tu C. W.
Published: January 2007

Secondary ion mass spectrometry and photoluminescence are employed to evaluate the origin and efficiency of hydrogen passivation of nitrogen in GaNAs and GaNP. The hydrogen profiles are found to closely follow the N distributions, providing unambiguous evidence for their preferential binding as the dominant mechanism for neutralization of N-induced modifications in the electronic structure of the materials. Though the exact number of H atoms involved in passivation may depend on the conditions of the H treatment and the host matrixes, it is generally found that more than three H atoms are required to bind to a N atom to achieve full passivation for both alloys.
Electrically driven light emission from single colloidal quantum dots at room temperature
Authors: Huang Hao , Dorn August , Bulovic Vladimir , Bawendi Moungi G.
Published: January 2007

Light emission from single colloidal CdSe∕ZnS (core/shell) nanocrystals embedded in electrically driven organic light emitting devices is demonstrated at room temperature. Spectral diffusion and blinking from individual quantum dots were observed both in electro- and photoluminescence. The authors propose a model in which the nanocrystals act as seeds for the formation of current channels that lead to enhanced exciton recombination in the vicinity of the quantum dots. This work demonstrates that individual semiconductor nanocrystals can serve as emissive probes in organic light emitting devices and that they can be used to manipulate device structure and properties at the nanometer scale.