bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of adsorption and decomposition of metal alkylamide precursors for ultrathin film growth
Authors: Rodríguez-Reyes Juan Carlos F. , Teplyakov Andrew V.
Published: October 2008

Atomic layer deposition film growth is usually characterized by the presence of a transient (nonlinear) regime, where surface reactions of precursors take place on the substrate, resembling the first stages of chemical vapor deposition and affecting the composition of the forming interface. Here, the adsorption and decomposition of tetrakis(dimethylamido)titanium, Ti[N(CH3)2]4, tetrakis(dimethylamido)zirconium, Zr[N(CH3)2]4, tetrakis(dimethylamido)hafnium, Hf[N(CH3)2]4, pentakis(dimethylamido)tantalum, Ta[N(CH3)2]5, and bis(t-butylimido)-bis(dimethylamido)tungsten, [(CH3)3CN]2W[N(CH3)2]2, on a silicon substrate are investigated using density functional methods. These alkylamides are widely used for deposition of both diffusion barriers and high-permittivity (high-κ) materials. Adsorption is found to be dissociative, with scission of metal-ligand bonds being more feasible than scission of N–C bonds, suggesting that decomposition of ligands is not favored at low temperatures. However, decomposition through C–H bond scission may ultimately lead to the formation of Si–C bonds, without significant kinetic requirements and producing highly stable structures. The overall feasibility of the adsorption/decomposition pathway outlined here explains the presence of carbon at the interface in alkylamide-based deposition schemes.
Structure and surface morphology of vapor deposited polycarbonate thin films
Authors: Vree C. , Mayr S. G.
Published: October 2008

Amorphous thin poly(bisphenol A carbonate) films are prepared on Si, SiO2, GaAs, and spin cast polycarbonate substrates by condensation from vapor. Surface morphologies are investigated using scanning force microscopy with focus on the substrate-film interface formation. Except for polycarbonate substrates, where smooth surfaces are observed for all film thicknesses, a change from rough discontinuous surfaces for very thin films to smooth homogeneous surfaces for thicker films appears due to dewetting effects. Utilizing Fourier transform infrared spectroscopy, size-exclusion chromatography, and mass spectrometry, we find that the bond topology stays mostly intact during evaporation, while the molecular weight as well as the chain length is reduced.
Electrical switching dynamics in circular and rectangular Ge2Sb2Te5 nanopillar phase change memory devices
Authors: Ozatay O. , Stipe B. , Katine J. A. , Terris B. D.
Published: October 2008

We have measured the critical phase change conditions induced by electrical pulses in Ge2Sb2Te5 nanopillar phase change memory devices by constructing a comprehensive resistance map as a function of pulse parameters (width, amplitude, and trailing edge). Our measurements reveal that the heating scheme and the details of the contact geometry play the dominant role in determining the final phase composition of the device, such that a nonuniform heating scheme using rectangular contacts promotes partial amorphization/crystallization in a wide range of pulse parameters enabling multiple resistance levels for data storage applications. Furthermore we find that fluctuations in the snap-back voltage and set/reset resistances in repeated switching experiments are related to the details of the current distribution, such that a uniform current injection geometry (i.e., circular contact) favors more reproducible switching parameters. This shows that possible geometrical defects in nanoscale phase change memory devices may play an essential role in the performance of the smallest possible devices through modification of the exact current distribution in the active chalcogenide layer. We present a three-dimensional finite element model of the electrothermal physics to provide insights into the underlying physical mechanisms of the switching dynamics as well as to quantitatively account for the scaling behavior of the switching currents in both circular and rectangular contact geometries. The calculated temporal evolution of the heat distribution within the pulse duration shows distinct features in rectangular contacts providing evidence for locally hot spots at the sharp corners of the current injection site due to current crowding effects leading to the observed behavior.
Fabrication of optical tips from photonic crystal fibers
Authors: Carlson Christine A. , Woehl Jörg C.
Published: October 2008

We present a procedure for fabricating optical tips from photonic crystal fibers which feature a solid core surrounded by a cladding with a hexagonal, multilayer arrangement of air channels running along the length of the fiber. Such optical tips may have unique advantages for the production of near-field optical aperture probes (i.e., metal-coated optical tips with a subwavelength aperture at the tip apex). With both cladding and core made of pure silica, these fibers are fluorescence-free; they support only a single mode over a broad wavelength range (covering the visible and near-infrared spectrum), which makes them useful for multicolor experiments; and they exhibit zero group velocity dispersion at visible wavelengths, which opens up the possibility of femtosecond applications in the near field. Our tip fabrication procedure leads to a sharp, protruding, central tip formed exclusively from the fiber core amidst a regular arrangement of smaller tips from the inner, microstructured region of the cladding. A mechanism for tip formation is proposed based on optical observations at various stages, which explains the self-centering nature of the process.
High resolution hard x-ray microscope on a second generation synchrotron source
Authors: Tian Yangchao , Li Wenjie , Chen Jie , Liu Longhua , Liu Gang , Tkachuk Andrei , Tian Jinping , Xiong Ying , Gelb Jeff , Hsu George , Yun Wenbing
Published: October 2008

A full-field, transmission x-ray microscope (TXM) operating in the energy range of 7–11 keV has been installed at the U7A beamline at the National Synchrotron Radiation Laboratory, a second generation synchrotron source operating at 0.8 GeV. Although the photon flux at sample position in the operating energy range is significantly low due to its relatively large emittance, the TXM can get high quality x-ray images with a spatial resolution down to 50 nm with acceptable exposure time. This TXM operates in either absorption or Zernike phase contrast mode with similar resolution. This TXM is a powerful analytical tool for a wide range of scientific areas, especially studies on nanoscale phenomena and structural imaging in biology, materials science, and environmental science. We present here the property of the x-ray source, beamline design, and the operation and key optical components of the x-ray TXM. Plans to improve the throughput of the TXM will be discussed.
Wave localization and density bunching in pair ion plasmas
Authors: Mahajan Swadesh M. , Shatashvili Nana L.
Published: October 2008

By investigating the nonlinear propagation of high intensity electromagnetic (EM) waves in a pair ion plasma, whose symmetry is broken via contamination by a small fraction of high mass immobile ions, it is shown that this new and interesting state of (laboratory created) matter is capable of supporting structures that strongly localize and bunch the EM radiation with density excess in the region of localization. Testing of this prediction in controlled laboratory experiments can lend credence, inter alia, to conjectures on structure formation (via the same mechanism) in the MEV era of the early universe.
Generation and dose distribution measurement of flash x-ray in KALI-5000 system
Authors: Menon Rakhee , Roy Amitava , Mitra S. , Sharma A. , Mondal J. , Mittal K. C. , Nagesh K. V. , Chakravarthy D. P.
Published: October 2008

Flash x-ray generation studies have been carried out in KALI-5000 Pulse power system. The intense relativistic electron beam has been bombarded on a tantalum target at anode to produce flash x-ray via bremsstrahlung conversion. The typical electron beam parameter was 360 kV, 18 kA, and 100 ns, with a few hundreds of A/cm2 current density. The x-ray dose has been measured with calcium sulfate:dysposium (CaSO4:Dy) thermoluminescent dosimeter and the axial dose distribution has been characterized. It has been observed that the on axis dose falls of with distance ∼1/xn, where n varies from 1.8 to 1.85. A maximum on axis dose of 46 mrad has been measured at 1 m distance from the source. A plastic scintillator with optical fiber coupled to a photomultiplier tube has been developed to measure the x-ray pulse width. The typical x-ray pulse width varied from 50 to 80 ns.
Autofluorescence insensitive imaging using upconverting nanocrystals in scattering media
Authors: Xu Can T. , Svensson Niclas , Axelsson Johan , Svenmarker Pontus , Somesfalean Gabriel , Chen Guanying , Liang Huijuan , Liu Haichun , Zhang Zhiguo , Andersson-Engels Stefan
Published: October 2008

Autofluorescence is a nuisance in the field of fluorescence imaging and tomography of exogenous molecular markers in tissue, degrading the quality of the collected data. In this letter, we report autofluorescence insensitive imaging using highly efficient upconverting nanocrystals (NaYF4:Yb3+∕Tm3+) in a tissue phantom illuminated with near-infrared radiation of 85mW∕cm2. It was found that imaging with such nanocrystals leads to an exceptionally high contrast compared to traditional downconverting fluorophores due to the absence of autofluorescence. Upconverting nanocrystals may be envisaged as important biological markers for tissue imaging purposes.
Electrochemical growth of ultraflat Au(111) epitaxial buffer layers on H–Si(111)
Authors: Prod’homme P. , Maroun F. , Cortès R. , Allongue P.
Published: October 2008

Thin metal layers deposited on a substrate (buffer layers) are widely employed in many fields of research and in microelectronic industry. In this work we present x-ray diffraction measurements and atomic force microscopy observations which demonstrate that high quality ultrathin Au(111) epitaxial films can be electrodeposited from a gold chloride solution on a well-defined H-terminated vicinal Si(111) surface. In addition, the obtained films present no apparent grain boundary. This result, which seems in conflict with classical growth theory, requires applying unconventional electrodeposition conditions in which a strong hydrogen evolution reaction is promoted.
The effect of DNA on mechanical properties of nanofiber hydrogels
Authors: Shin Min Kyoon , Kim Shi Hyeong , Jung Sung-il , Kim Sun I. , Kim Seon Jeong , Kim Byung Joo , So Insuk
Published: October 2008

Uniform poly(vinyl alcohol) (PVA) nanofiber gels incorporating double-stranded deoxyribonucleic acid (DNA) were fabricated without the aid of cross-linkers employing electrospinning. Creep and tensile tests of the DNA/PVA nanofiber gels were carried out in an aqueous medium to analyze interactions between the DNA and PVA. The DNA/PVA gels had a higher elastic modulus than the PVA gel. The viscosity with increasing external load was calculated by applying the Burger model to the creep curves. We conclude that DNA is relatively weakly bound with the PVA chains, although the elastic modulus of the DNA/PVA gels was higher than that of PVA gel.
Theoretical prediction and experimental evidence for thermodynamic properties of metastable liquid Fe–Cu–Mo ternary alloys
Authors: Wang H. P. , Wei B.
Published: October 2008

The prediction of thermodynamic properties for metastable undercooled liquid is important in the research on liquid structure and phase transition. Here we report the theoretical prediction of specific heat for metastable undercooled liquid Fe–Cu–Mo ternary alloys with a molecular dynamics method. Furthermore, experimental measurements were also performed by electromagnetic levitation drop calorimeter to confirm the predicted results. For liquid Fe78Cu15Mo7 and Fe71.5Cu3.5Mo25 alloys, the calculated specific heat values are 37.5 and 36.3 J mol−1 K−1, which agree well with the experimental results of 40.0 and 38.3 J mol−1 K−1, respectively. The computed undercooling range of about 700 K is sufficiently broader than the experimental regime of 223 K.
Separation of the Schottky barrier and polarization effects on the photocurrent of Pt sandwiched Pb(Zr0.20Ti0.80)O3 films
Authors: Zheng Fengang , Xu Jie , Fang Liang , Shen Mingrong , Wu Xinglong
Published: October 2008

Photoelectric behavior of Pt sandwiched Pb(Zr0.20Ti0.80)TiO3 (PZT) films deposited on Pt∕Ti∕SiO2∕Si substrates by a sol-gel method was investigated by testing the short-circuit photocurrent under different film thicknesses. By poling the films step by step with increased magnitude and alternated direction of the dc electric field, interesting photoelectric behavior was found when the PZT films were in virgin or poled up/down state. The photocurrent was also strongly dependent on the film thickness. A simple model was proposed to separate the effects of interface Schottky barriers and bulk ferroelectric polarization of the film on the photocurrent of the Pt/PZT/Pt structure.
Optical property of beta barium borate in terahertz region
Authors: Liu Jingle , Guo Xiaoyu , Dai Jianming , Zhang X.-C.
Published: October 2008

The optical property of beta barium borate (β−BBO) in the terahertz region (0.2–12THz) was studied using a broadband air photonic terahertz time-domain spectrometer. The crystal orientation and frequency dependence of β−BBO refractive index and absorption coefficient were experimentally investigated over the temperature range of 10–293K. Four TO phonon modes were observed below 3.5THz. The behavior of these phonon modes at different temperatures has been characterized.
Training Eye Movements: Can Training People Where to Look Hinder the Processing of Fixated Objects?
Authors: Dewhurst Richard , Crundall David
Published: October 2008

An experiment designed to test the effects of different forms of training in a visual-search-like task is reported. Observers were presented with a series of displays containing a central letter and a ring of peripheral characters, one of which was a digit. Odd digits (catch trials) required a space-bar response; even digits required a different response contingent on the identity of the central letter. Two forms of training provided information either about the location of the peripheral digit, or about a quick way to classify the central letter. The aim was to relate training to Findlay and Walker's (1999, Behavioral and Brain Sciences22 661–721) model of saccadic eye-movement control by affecting the hypothesised Move and Fixate centres respectively. The results showed that training benefited search, but training of the Move centre alone generated significantly longer re-inspections of the central region (in a feedback condition). This highlights that the emphasis often placed upon broadening the range of visual search when training eye movements may be misplaced. More specifically, special attention should be given, not only to advising people how to move their eyes, but also to improving the ability to effectively process important visual stimuli when fixating.
Efficiency of top-down control depends on nutrient concentration in a Mediterranean shallow lake: A mesocosm study
Authors: Blanco Saúl , Fernández-Aláez Margarita , Bécares Eloy
Published: October 2008

In shallow lakes, the influence of top-down control is considered to be less important under a Mediterranean bioclimate, although little experimental data support this hypothesis. The present study aimed to experimentally assess the importance of top-down forces in the trophic status of Mediterranean shallow lakes. A bifactorial mesocosm experiment was carried out in a shallow lake using a range of nutrient concentrations and fish population densities. The results demonstrated an expected increase in turbidity levels as nutrients and fish density increased, as a result of both sediment resuspension and chlorophyll a concentrations. Nevertheless, at higher nutrient additions, turbidity decreased in the mesocosms in response to cladoceran proliferation because the fishes were unable to control zooplankton growth under such conditions. Fish diet content analysis showed a generalist diet with an important contribution of non-planktonic components; the proportion of zooplankton in the diet contents increased with nutrient additions. Fishes preferred cladocerans over copepods and rotifers, these latter taxa dominated the resulting zooplankton community. Some fish-added mesocosms retained high transparency levels, most likely because of physiological changes in response to high ammonium concentrations. In summary, the dietary spectrum of Chondrostoma arcasii [Steindachner], despite some electivity patterns, depends largely on available resources. The trophic ecology of cyprinids, acting both through direct and indirect effects on food webs, is a determinant factor explaining, in part, stable high turbidity levels in many shallow lakes.
Specific dynamic action as an indicator of carbohydrate digestion in juvenile spiny lobsters, Jasus edwardsii
Authors: Radford C. A. , Marsden I. D. , Jeffs A. G.
Published: October 2008

Commercial aquaculture of crustaceans depends on the development of artificial diets, the effectiveness of which is usually determined from captive growth experiments. As an alternative, this research examines the use of a physiological measure of energy expenditure, the specific dynamic action (SDA) using closed box respirometry to determine the potential of different carbohydrates for artificial diets for the spiny lobster Jasus edwardsii. Juvenile lobsters were provided with meals composed of glycogen, maltose, sucrose, glucose, or fructose in a gelatine base, or with gels of the algal carbohydrates, agar, alginate and carrageenan. Lobsters feeding on most of the general carbohydrate diets elicited a typical SDA response with an immediate rise in oxygen consumption, which was not exhibited in unfed controls. Lobsters fed algal carbohydrates did not show a SDA response but did show an increase in ammonia excretion. It is concluded that spiny lobsters are able to use carbohydrates as part of their diet and the SDA provides a useful means of rapidly determining which carbohydrates may be best used in formulated diets. It is suggested that the SDA would be a quick and effective way to determine food digestibility of components or ingredients used in crustacean aquaculture.
Microsatellites-based genetic analysis of the Lophiidae fish in Europe
Authors: Blanco G. , Borrell Y. J. , Cagigas M. E. , Vázquez E. , Prado J. A. Sánchez
Published: October 2008

The anglerfish species Lophius piscatorius and Lophius budegassa are among the most valuable fishes sought after by bottom fisheries in western and southern European waters. It is currently believed that there are two stocks for each of the two species, north and south, which determine their assessment and management. A genetic analysis using eight polymorphic microsatellite markers was carried out on samples collected from western European waters and the south-western Mediterranean Sea. The results strongly suggest that the boundary between northern and southern stocks is not genetically supported. However, populations were not genetically homogeneous. Besides a pattern of genetic differentiation between Mediterranean and the rest of the samples, the L. budegassa samples taken from the Spain Atlantic zone and from the Portugal Atlantic zone were genetically distinct, whereas the samples taken in the French Atlantic zone for the L. piscatorius species seem to be different from the rest of the samples under study. This can be indicative of a more subtle genetic structure that deserves more study for guaranteeing adequate fishery management of these species.
Predicting the slope of the allometric scaling of consumption rates in fish using the physiology of growth
Authors: Wiff Rodrigo , Roa-Ureta Rubén
Published: October 2008

Allometric scaling (where body size features as the independent variable) has been observed in many aspects of fish biology. Empirical studies have shown that individual and population rates of food consumption for single and multi-species datasets show positive allometry. However, the ratio of population consumption to biomass shows negative allometry when evaluated across species. In this paper, a theoretical explanation is proposed that predicts the magnitudes and signs of the allometric slopes for consumption and consumption/biomass within and among species. It is proposed that the ultimate cause of the allometries related to food consumption in fish lies in the physiology of growth. In the context of von Bertalanffy growth, the allometric slopes are caused by the constraints imposed on anabolism by the surfaces absorbing oxygen, by the volumetric relationship between linear body size and body mass, and by a dimensionless growth parameter.
Round scallops and square meshes: a comparison of four codend types on the catch rates of target species and by-catch in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery
Authors: Courtney Anthony J. , Campbell Matthew J. , Roy Darren P. , Tonks Mark L. , Chilcott Keith E. , Kyne Peter M.
Published: October 2008

Concern over the amount of by-catch from benthic trawl fisheries and research into the problem have increased in recent years. The present paper demonstrated that by-catch rates in the Queensland (Australia) saucer scallop (Amusium balloti) trawl fishery can be reduced by 77% (by weight) using nets fitted with a turtle excluder device (TED) and a square-mesh codend, compared with a standard diamond-mesh codend with no TED. This large reduction was achieved with no significant effect on the legal size scallop catch rate and 39% fewer undersize scallops were caught. In total, 382 taxa were recorded in the by-catch, which was dominated by sponges, portunid crabs, small demersal and benthic fish (e.g. leatherjackets, stingerfish, bearded ghouls, nemipterids, longspine emperors, lizard fish, triggerfish, flounders and rabbitfish), elasmobranchs (e.g. mainly rays) and invertebrates (e.g. sea stars, sea urchins, sea cucumbers and bivalve molluscs). Extremely high reductions in catch rate (i.e. ≥85%) were demonstrated for several by-catch species owing to the square-mesh codend. Square-mesh codends show potential as a means of greatly reducing by-catch and lowering the incidental capture and mortality of undersize scallops and Moreton Bay bugs (Thenus australiensis) in this fishery.
Assessment of health‐related quality of life: Swedish version of polycystic ovary syndrome questionnaire
Authors: JEDEL ELIZABETH , KOWALSKI JAN , STENER‐VICTORIN ELISABET
Published: October 2008

Objective. Polycystic ovary syndrome questionnaire (PCOSQ) was developed in USA to ascertain specific health‐related quality of life (HRQL) in polycystic ovary syndrome (PCOS). The Swedish version of PCOSQ should be tested prior to its use in research and clinical practice and the aims of the study were as follows: (a) determine the test–retest reliability and (b) confirm the domain structure of the Swedish version of PCOSQ; a 26‐item questionnaire, divided into the five domains: emotions, body hair, weight concerns, infertility concerns and menstrual irregularities. Methods. PCOSQ translation from English to Swedish was followed by a test–retest and a factor analysis of obtained PCOSQ completed twice by 69 women with PCOS. Results. The median age was 30 (21–37) years. The Kappa (κ) statistic for the five domains ranged from 0.29 to 0.69 demonstrating fair to good agreement among items. The Intra‐class Correlation Coefficient (ICC) for the five domains was high to excellent ranging from 0.79 to 0.96. The factor analysis presented six domains and the original domain structure was partly confirmed. Conclusions. The Swedish version of PCOSQ is reliable and can be used to measure HRQL in PCOS. Researchers and clinicians should be aware of the benefits of PCOSQ.
Uterine artery Doppler velocimetry and maternal weight gain by the mid‐second trimester for prediction of fetal growth restriction
Authors: KWON HAN‐SUNG , KIM YOUNG‐HAN , PARK YONG‐WON
Published: October 2008

Objective. To investigate whether assessment of maternal weight gain up to mid‐second trimester improves the predictive value of uterine artery Doppler velocimetry (UAD) for the prediction of fetal growth restriction (FGR). Setting. Department of Obstetrics and Gynecology, Yonsei University College of Medicine. Design. Prospective Doppler measurements coupled to retrospective chart review. Population. A total of 10,970 women delivering at the institution. Outcome measures. Maternal weight gain up to mid‐second trimester and Doppler ultrasonography on bilateral uterine arteries between 20 and 24 weeks’ gestation. Low weight gain was defined as <0.2 kg/week and FGR as birthweight of <10th percentile. Results. ith that combined with the measurement of maternal weight gain for the prediction of the FGR. The odd ratios for FGR were 2.56 (95% CI 1.59–4.12) in the group with normal UAD and abnormal weight gain (normal‐abnormal group), 1.91 (95% CI 0.98–3.7) in the abnormal‐normal group and 40.3 (95% CI 16.9–96.4) in the abnormal‐abnormal group. UAD independent of weight gain had a sensitivity of 31.5%, a specificity of 88%, a positive predictive value (PPV) of 24.5% and a negative predictive value (NPV) of 91.2%. When mid‐trimester maternal weight gain was accounted for, the sensitivity of UAD was 64.9%, specificity 64.1%, PPV 73.3% and NPV 93.6%. Conclusion. The diagnostic performance of UAD for FGR improved significantly when the degree of maternal weight gain until the mid‐second trimester was taken into account. Closer antenatal surveillance might be required in women with abnormal uterine Doppler velocimetry if their mid‐second trimester weight gain is poor.
The use of non‐three‐layer ultrasound in biopsy recommendation for premenopausal women
Authors: ABE MASAKAZU , OGAWA HIROSHI , AYHAN AYSE
Published: October 2008

Objective. To evaluate diagnostic accuracy and timing of abnormal transvaginal ultrasonography for the recommendation of endometrial biopsy among premenopausal patients with abnormal uterine bleeding. Design. Two‐hundred and thirteen transvaginal ultrasonograms of premenopausal women with abnormal uterine bleeding were retrospectively evaluated. Main outcome measures. ‘Abnormal’ ultrasonography was defined as either non‐three‐layer appearance during the proliferative phase or thickening ≥15mm during the secretory/unknown phase. Findings were assessed on the basis of the histological diagnosis of the biopsies taken as the reference standard. Accuracy of the defined criteria with their likelihood ratio for detection of an endometrial disease was calculated. Results. Abnormal histopathologic findings were detected in 147 (69%) of 213 patients. ‘Abnormal’ transvaginal ultrasonography criteria could detect disease states in 90.3% of patients with a sensitivity of 94.6% and a specificity of 77.2% (p <0.01). Sensitivity and specificity increased to 97.1 and 84.4% for ultrasonography conducted during the proliferative phase and were 60 and 61.9% for the secretory/unknown phase, respectively. Better results were clearly found for ultrasonograms obtained during the proliferative phase (p <0.01). The inclusion of post‐biopsy proliferative phase transvaginal ultrasonography data of the following cycle resulted in a sensitivity of 95.2% and a specificity of 89.4%. Conclusions. The application of transvaginal ultrasonography using non‐three‐layer criteria is a highly accurate first step for the selection of premenopausal patients with abnormal uterine bleeding, which may reduce the number of unnecessary endometrial biopsies by approximately 25%. Proliferative phase evaluation is preferable.
Prospective follow‐up of menstrual disorders in adolescence and prognostic factors
Authors: WIKSTEN‐ALMSTRÖMER MARIANNE , HIRSCHBERG ANGELICA LINDÉN , HAGENFELDT KERSTIN
Published: October 2008

Objective. Clinical follow‐up of menstrual status and eating behavior in grown‐up women diagnosed with menstrual disturbance in adolescence. Design. Prospective follow‐up study six years after the initial study. Setting. A youth clinic that is part of the school health system in Stockholm. Population. Eighty‐seven women diagnosed with secondary amenorrhea or oligomenorrhea in adolescence. Methods. Subjects underwent gynecological examination, evaluation of eating behavior and endocrine status. Main outcome measures. Menstrual status and eating behavior changes. Results. Menstrual disturbances were still present in 62% of the subjects not using hormonal contraception, 59% of which fulfilled the criteria for polycystic ovary syndrome (PCOS). The frequency of persistent menstrual disturbance was significantly more common in women with previous oligomenorrhea than secondary amenorrhea. The occurrence of eating disorders was decreased by half to 31% in women diagnosed with secondary amenorrhea at the initial study, whereas it was unchanged (40%) in women with previous oligomenorrhea. Recovery from anorectic behavior, primarily in the group of secondary amenorrhea, significantly predicted resumption with menses. Conclusion. Menstrual disturbances and eating disorders were still frequent after six years in a follow‐up of women who had menstrual disturbance in adolescence. PCOS was the main cause explaining persistent menstrual disorder, whereas recovery of anorectic eating disorders predicted resumption of menses. The findings call for a continued follow‐up of women diagnosed with menstrual disturbance in their teens.
Properties of the Inner Pore Region of TRPV1 Channels Revealed by Block with Quaternary Ammoniums
Authors: Jara-Oseguera Andrés , Llorente Itzel , Rosenbaum Tamara , Islas León D.
Published: October 2008

The transient receptor potential vanilloid 1 (TRPV1) nonselective cationic channel is a polymodal receptor that activates in response to a wide variety of stimuli. To date, little structural information about this channel is available. Here, we used quaternary ammonium ions (QAs) of different sizes in an effort to gain some insight into the nature and dimensions of the pore of TRPV1. We found that all four QAs used, tetraethylammonium (TEA), tetrapropylammonium (TPrA), tetrabutylammonium, and tetrapentylammonium, block the TRPV1 channel from the intracellular face of the channel in a voltage-dependent manner, and that block by these molecules occurs with different kinetics, with the bigger molecules becoming slower blockers. We also found that TPrA and the larger QAs can only block the channel in the open state, and that they interfere with the channel's activation gate upon closing, which is observed as a slowing of tail current kinetics. TEA does not interfere with the activation gate, indicating that this molecule can reside in its blocking site even when the channel is closed. The dependence of the rate constants on the size of the blocker suggests a size of around 10 Å for the inner pore of TRPV1 channels.
Rescue of Volume-regulated Anion Current by Bestrophin Mutants with Altered Charge Selectivity
Authors: Chien Li-Ting , Hartzell H. Criss
Published: October 2008

Mutations in human bestrophin-1 are linked to various kinds of retinal degeneration. Although it has been proposed that bestrophins are Ca2+-activated Cl− channels, definitive proof is lacking partly because mice with the bestrophin-1 gene deleted have normal Ca2+-activated Cl− currents. Here, we provide compelling evidence to support the idea that bestrophin-1 is the pore-forming subunit of a cell volume-regulated anion channel (VRAC) in Drosophila S2 cells. VRAC was abolished by treatment with RNAi to Drosophila bestrophin-1. VRAC was rescued by overexpressing bestrophin-1 mutants with altered biophysical properties and responsiveness to sulfhydryl reagents. In particular, the ionic selectivity of the F81C mutant changed from anionic to cationic when the channel was treated with the sulfhydryl reagent, sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES−) (PCs/PCl = 0.25 for native and 2.38 for F81C). The F81E mutant was 1.3 times more permeable to Cs+ than Cl−. The finding that VRAC was rescued by F81C and F81E mutants with different biophysical properties shows that bestrophin-1 is a VRAC in S2 cells and not simply a regulator or an auxiliary subunit. F81C overexpressed in HEK293 cells also exhibits a shift of ionic selectivity after MTSES− treatment, although the effect is quantitatively smaller than in S2 cells. To test whether bestrophins are VRACs in mammalian cells, we compared VRACs in peritoneal macrophages from wild-type mice and mice with both bestrophin-1 and bestrophin-2 disrupted (best1−/−/best2−/−). VRACs were identical in wild-type and best1−/−/best2−/− mice, showing that bestrophins are unlikely to be the classical VRAC in mammalian cells.
hERG Gating Microdomains Defined by S6 Mutagenesis and Molecular Modeling
Authors: Wynia-Smith Sarah L. , Gillian-Daniel Anne Lynn , Satyshur Kenneth A. , Robertson Gail A.
Published: October 2008

Human ether-à-go-go–related gene (hERG) channels mediate cardiac repolarization and bind drugs that can cause acquired long QT syndrome and life-threatening arrhythmias. Drugs bind in the vestibule formed by the S6 transmembrane domain, which also contains the activation gate that traps drugs in the vestibule and contributes to their efficacy of block. Although drug-binding residues have been identified, we know little about the roles of specific S6 residues in gating. We introduced cysteine mutations into the hERG channel S6 domain and measured mutational effects on the steady-state distribution and kinetics of transitions between the closed and open states. Energy-minimized molecular models based on the crystal structures of rKv1.2 (open state) and MlotiK1 and KcsA (closed state) provided structural contexts for evaluating mutant residues. The majority of mutations slowed deactivation, shifted conductance voltage curves to more negative potentials, or conferred a constitutive conductance over voltages that normally cause the channel to close. At the most intracellular extreme of the S6 region, Q664, Y667, and S668 were especially sensitive and together formed a ringed domain that occludes the pore in the closed state model. In contrast, mutation of S660, more than a full helical turn away and corresponding by alignment to a critical Shaker gate residue (V478), had little effect on gating. Multiple substitutions of chemically distinct amino acids at the adjacent V659 suggested that, upon closing, the native V659 side chain moves into a hydrophobic pocket but likely does not form the occluding gate itself. Overall, the study indicated that S6 mutagenesis disrupts the energetics primarily of channel closing and identified several residues critical for this process in the native channel.
Measurements of the BKCa Channel's High-Affinity Ca2+ Binding Constants: Effects of Membrane Voltage
Authors: Sweet Tara-Beth , Cox Daniel H.
Published: October 2008

It has been established that the large conductance Ca2+-activated K+ channel contains two types of high-affinity Ca2+ binding sites, termed the Ca2+ bowl and the RCK1 site. The affinities of these sites, and how they change as the channel opens, is still a subject of some debate. Previous estimates of these affinities have relied on fitting a series of conductance–voltage relations determined over a series of Ca2+ concentrations with models of channel gating that include both voltage sensing and Ca2+ binding. This approach requires that some model of voltage sensing be chosen, and differences in the choice of voltage-sensing model may underlie the different estimates that have been produced. Here, to better determine these affinities we have measured Ca2+ dose–response curves of channel activity at constant voltage for the wild-type mSlo channel (minus its low-affinity Ca2+ binding site) and for channels that have had one or the other Ca2+ binding site disabled via mutation. To accurately determine these dose–response curves we have used a series of 22 Ca2+ concentrations, and we have used unitary current recordings, coupled with changes in channel expression level, to measure open probability over five orders of magnitude. Our results indicate that at −80 mV the Ca2+ bowl has higher affinity for Ca2+ than does the RCK1 site in both the opened and closed conformations of the channel, and that the binding of Ca2+ to the RCK1 site is voltage dependent, whereas at the Ca2+ bowl it is not.
Agency Costs of Overvalued Equity
Authors: Jensen Michael C.
Published: October 2008

I define and analyze the agency costs of overvalued equity. They explain the dramatic increase in corporate scandals and value destruction in the last five years; costs that have totaled hundreds of billions of dollars. When a firm's equity becomes substantially overvalued it sets in motion a set of organizational forces that are extremely difficult to manage—forces that almost inevitably lead to destruction of part or all of the core value of the firm. WorldCom, Enron, Nortel, and eToys are only a few examples of what can happen when these forces go unmanaged. Because we currently have no simple solutions to the agency costs of overvalued equity this is a promising area for future research.
Measuring Investment Distortions when Risk‐Averse Managers Decide Whether to Undertake Risky Projects
Authors: Parrino Robert , Poteshman Allen M. , Weisbach Michael S.
Published: October 2008

We create a dynamic model in which a self‐interested, risk‐averse manager makes corporate investment decisions at a levered firm with characteristics typical of public US firms. We examine the magnitude of distortions in those decisions when a new project changes firm risk and find expected changes in the values of future tax shields and bankruptcy costs to be important factors. We evaluate the extent to which these distortions vary with firm leverage, debt duration, project size, managerial risk aversion, managerial non‐firm wealth, and the structure of management compensation packages
Cross‐Listings and M&A Activity: Transatlantic Evidence
Authors: Tolmunen Pasi , Torstila Sami
Published: October 2008

We analyze whether European firms choose to list shares in the US to facilitate acquisitions. Evidence from a sample of 547 European companies shows that cross‐listed firms are significantly more active in acquiring US companies than are their domestically listed peers. This pattern holds even after we account for self‐selection in the cross‐listing decision. Cross‐listed firms are also more likely to use equity payment in large transactions, but after taking self‐selection into account, transaction size becomes the key determinant of the use of equity. After cross‐listing, the proportion of aggregate M&A volume financed with equity increases.
Do Invesrtors Capture the Value Premium?
Authors: Houge Todd , Lughran Tim
Published: October 2008

Do investors realize higher returns by investing in value stocks instead of gorwth stocks? Examination of a sample of equity indexes, mutual funds, and large‐cap stocks reveals no evidence that value firms have earned higher returns than growth firms. The value premium reported in the literarture is historically strongest for small‐capitalization firms, yea average annual rerturns for small‐cap equity funds are 14.10% for value funds compared to 14.52% for growth funds. Despite dramatic increases in mutual fund expense ratios from 1965 to 2001, fee differences across style funds cannot explain the absence of a value premium.
The Dynamic Relation Between Returns and Idiosyncratic Volatility
Authors: Jiang Xiaoquan , Lee Bong‐Soo
Published: October 2008

We claim that regressing excess returns on one‐lagged volatility provides only a limited picture of the dynamic effect of idiosyncratic risk, which tends to be persistent over time. By correcting for the serial correlation in idiosyncratic volatility, we find that idiosyncratic volatility has a significant positive effect. This finding seems robusrt for various firm size portfolios, sample periods, and measures of idiosyncratic risk. Our findings suggest stock markets mis‐price idiosyncratic risk. There may be some measurement problems with idiosyncratic risk. There may be some measurement problems with idiosyncratic risk that could be related to nondiversifiable risk.
The Determinants and Implications of Mutual Fund Cash Holdings: Theory and Evidence
Authors: Yan Xuemin (Sterling)
Published: October 2008

In this article, I examine the determinants and implications of equity mutual fund cash holdings. In cross‐sectional tests, I find evidence generally supportive of a static trade‐off model developed in the article. In particular, small‐cap funds and funds with more‐volatile fund flows hold more cash. However, I do not find that fund managers with better stock‐picking skills hold less cash. Aggregate cash holdings by equity mutual funds are persistent and positively related to lagged aggregate fund flows. Aggregate cash holdings do not forecast future market returns, suggesting that equity funds as a whole do not have market timing skills.
Explaining Premiums in Restricted DR Markets and Theri Implicartions: The Case of Infosys
Authors: Puthenpurackal John
Published: October 2008

I examine several possible explanations for why Infosys' Deposirtary Receipts (DRs) trade at significant premiums to the equivalent underlying domestic shares. I find that a limited supply of DRs and a downwoard‐sloping demand curve, significant transaction costs associated with investing directly in the domestic market, and trend‐chasing by smaller and potentially uninformed investors partly explain the DR premiums. I also examine the wealth effects of non‐capital raising secondary depositary receipt offerings by Infosys Technologies and find significant wealth transfers from existing DR holders to selling domestic shareholders who are comprised significantly of Infosys' founders.
Value, Survival, and the Evolution of Firm Organizational Structure
Authors: Borghesi Richard , Houston Joel , Naranjo Andy
Published: October 2008

We examine corporate product diversification as a dynamic process. Consistent with prior research, we find that the average diversification discount is about 8% when using the standard value‐multiple approach. However, we find that a significant portion of the diversification discount arises from benchmark comparisons of value ratios of mature firms with those of very young firms that are more likely to have high value multiples. The magnitude of the diversification discount falls by 15% to 30% when we control for firm age. We also show that diversification reduces the mortality rate of firms, and we provide evidence that mature firms pursue diversification strategies partly as a means to exit stagnant business segments for industries that are more highly valued.
The Importance of Cash‐Flow News for Financially Distressed Firms
Authors: Eisdorfer Assaf
Published: October 2008

Previous studies have shown that stock prices are moved primarily by news about discount rates (expected returns). I argue that when a firm experiences financial distress, news about cashflows becomes more dominant in driving its stock returns. Applying Campbell's (1991) variance decomposition framework to financially distressed firms supports this argument. Furthermore, I find that more bankruptcies occur after negative shocks to expected cashflows than after positive shocks to discount rates; and that stock prices of distressed firms are less sensitive than those of sound firms to changes in equity risk.
Lockup and Voluntary Earnings Forecast Disclosure in IPOs
Authors: Chong Beng Soon , Ho Kim Wai
Published: October 2008

We examine the relation between lockup length and voluntary earnings forecast disclosures for IPOs in Singapore. Unlike firms in the United States, companies in Singapore are allowed to provide earnings forecasts in their IPO prospectuses. We find that forecasters are more likely to accept longer lockup periods, so that the lockup expires after the first post‐IPO earnings announcement. Our study also shows that because the lockup agreement removes personal incentives to issue aggressive forecasts, IPO firms tend to issue conservative forecasts. Overall, our results suggest that the lockup mechanism adds credibility to the earnings forecast given in the IPO prospectus.
Firm Performance: Do Non‐Executive Directors Have Minds of their Own? Evidence from UK Panel Data
Authors: Mura Roberto
Published: October 2008

I investigate the relation between firm performance and both ownership structure and board composition. Use of the GMM methodology permits simultaneous control of both endogeneity of the independent variables and fixed effects. The data comprise an original, large, hand‐collected panel dataset of UK firms for the period 1991–2001. Results indicate that the direction of causality runs from ownership and board composition to performance. I find a cubic relation between performance and ownership by executive directors. The proportion of non‐executives on the board, but not their proportional ownership, is significantly and positively related to firm performance. Finally, the relation between performance and blockholdings by institutional and non‐institutional owners is negative. Thus, results indicate that only non‐executive directors are effective monitors.
Growth Options, Beta, and the Cost of Capital
Authors: Bernardo Antonio E. , Chowdhry Bhagwan , Goyal Amit
Published: October 2008

We show how to decompose a firm's beta into its beta of assets‐in‐place and its beta of growth opportunities. Our empirical results demonstrate that the beta of growth opportunities is greater than the beta of assets‐in‐place for virtually all industries over all periods of time dating back to 1977. The difference has important implications for determining the cost of capital. For example, when choosing comparables to determine a project beta one should match the growth opportunities of the project with those of the comparable firm. Assuming a 6% market equity risk premium, accounting for growth opportunities alters the project cost of capital by as much as 2% to 3%.
Takeover Activity as a Response to Time‐Varying Changes in Investment Opportunity Sets: Evidence from Takeover Sequences
Authors: Klasa Sandy , Stegemoller Mike
Published: October 2008

We study takeover sequences that contain at least five acquisitions made over a period greater than 12 months, with no two acquisitions separated by more than 24 months. Acquisitions made within such sequences represent more than a quarter of aggregate takeover activity by U.S. public firms from 1982–1999. Our fi ndings are consistent with a proposition that takeover sequences occur in the context of time‐varying changes in an acquirer's growth opportunity set. Takeover sequences begin (end) subsequent to an expansion (contraction) of this opportunity set.
IPO Underpricing, Firm Quality, and Analyst Forecasts
Authors: Zheng Steven X. , Stangeland David A.
Published: October 2008

We find that IPO underpricing is positively related to post‐IPO growth in sales and EBITDA, but is not significantly related to growth in earnings. Our evidence suggests that accrual reversals or earnings management may cause this inconsistency. We interpret the growth rates of sales and EBITDA as measures of firm quality, and conclude that our evidence supports the notion that IPO firms with greater underpricing are of better quality. Our tests on analysts' earnings forecast errors show that analysts are less positively biased in their earnings forecasts for IPO firms that have greater underpricing.