bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Non-Steady-State Perfusion on Xenon-133 Cerebral Blood Flow Measurements: An Analytical Study
Authors: Jaggi Jurg L. , Noordergraaf Abraham
Published: April 2011

Activation studies employing the noninvasive xenon-133 technique are widely used to investigate the cerebral circulation. Typical examples are the investigation of hemispheral specialization of higher cortical function with cognitive activation or the assessment of the hemodynamic reserve in occlusive cerebrovascular disease by CO2 inhalation. Traditionally, in studies using this technique, there is the requirement of a circulatory steady state during the measurement. Due to limitations in the duration of the stimulus or habituation to the stimulus, the basic assumption is often violated. In this study we investigated with the aid of a computer model to what extent blood flow measurement results are affected by non-steady-state blood flow. The findings indicate that cortical activation need not extend throughout the whole measurement to be detectable. Maintenance of activation for at least 5 min is sufficient for a successful measurement. In addition, the results show that the activation should be fully established when the measurement starts to achieve maximal sensitivity. Delay in activating the circulation will result in attenuated responses, especially if the stimulus is delayed beyond 2 min.
Mechanisms of Brain Ion Homeostasis during Acute and Chronic Variations of Plasma Potassium
Authors: Stummer Walter , Betz A. Lorris , Keep Richard F.
Published: April 2011

Brain and CSF potassium concentrations are well regulated during acute and chronic alterations of plasma potassium. In a previous study, we have shown that during chronic perturbations, regulation is achieved by appropriate adaptation of potassium influx, but that the degree of such adaptation during acute perturbations is much less. To elucidate further potential regulatory mechanisms, rats were rendered acutely or chronically hyper- or hypokalemic (range 2.7–7.6 m M). Measurements were made of brain and CSF water and ion contents to examine whether regulation occurred by modulation of K+ uptake into parenchymal cells. Furthermore, the permeability-surface area products (PSs) of 22Na+ were determined, because changes in K+ efflux via Na+,K+-ATPase on the brain-facing side of the blood–brain barrier might be reflected in modified Na+ permeability. Brain and CSF K+ concentrations and Na PS were all independent of chronic changes in plasma K+ and acute hypokalemia, suggesting that neither modulation of parenchymal K+ uptake nor K+ efflux via the Na+,K+-ATPase is involved in extracellular K+ regulation in these conditions. In contrast, Na PSs were increased by 40% (p < 0.05) in acute hyperkalemia. This was accompanied by a slight loss of tissue K+ and water from the intracellular space. These results suggest that increased potassium influx in acute hyperkalemia is compensated by stimulation of K+ efflux via Na+,K+-ATPase. A slight degree of overstimulation, as indicated by a net loss of tissue K+, leads us to hypothesize that other factors, apart from the kinetic characteristics of Na+,K+-ATPase, may regulate this enzyme at the blood–brain barrier.
Inducible Nitric Oxide Synthase Gene Expression in Brain following Cerebral Ischemia
Authors: Iadecola Costantino , Zhang Fangyi , Xu Sherry , Casey Robyn , Ross M. Elizabeth
Published: April 2011

Cerebral ischemia is followed by a local inflammatory response that is thought to participate in the extension of the tissue damage occurring in the postischemic period. However, the mechanisms whereby the inflammation contributes to the progression of the damage have not been fully elucidated. In models of inflammation, expression of the inducible isoform of nitric oxide synthase (iNOS) is responsible for cytotoxicity through the production of large amounts of nitric oxide (NO). In this study, therefore, we sought to establish whether iNOS is expressed in the ischemic brain. Rats were killed 6 h to 7 days after occlusion of the middle cerebral artery. iNOS expression in the ischemic area was determined by reverse-transcription polymerase chain reaction. Porphobilinogen deaminase mRNA was detected in the same sample and used for normalization. In the ischemic brain, there was expression of iNOS mRNA that began at 12 h, peaked at 48 h, and returned to baseline at 7 days (n = 3/time point). iNOS mRNA expression paralleled the time course of induction of iNOS catalytic activity, determined by the citrulline assay (17.4 ± 4.4 pmol citrulline/μg protein/min at 48 h; mean ± SD; n = 5 per time point). iNOS immunoreactivity was seen in neutrophils at 48–96 h after ischemia. The data provide molecular, biochemical, and immunocytochemical evidence of iNOS induction following focal cerebral ischemia. These findings, in concert with our recent demonstration that inhibition of iNOS reduces infarct volume in the same stroke model, indicate that NO production may play an important pathogenic role in the progression of the tissue damage that follows cerebral ischemia.
Temporal Profile of in situ DNA Fragmentation after Transient Middle Cerebral Artery Occlusion in the Rat
Authors: Li Yi , Chopp Michael , Jiang Ning , Yao Fayi , Zaloga Cecylia
Published: April 2011

We measured the temporal profile and anatomic distribution of cells exhibiting DNA fragmentation at various durations of reperfusion after middle cerebral artery (MCA) occlusion in the rat. Focal cerebral ischemia was induced in male Wistar rats (n = 62) using an intraluminal monofilament blockade of the MCA. After 2 h of MCA occlusion, the animals were killed at different durations of reperfusion (0.5, 3, 6, 9, and 12 h and 1, 2, 4, 7, 14, 21, and 28 days, n = 4 per time point). Sham-operated rats (n = 4) and normal rats not subjected to any surgical procedure (n = 4) were used as controls. Coronal brain sections (5 μm) were analyzed, using an in situ ApopTag kit, hematoxylin and eosin, and immunohistochemical double-staining methods. Six rats subjected to 2 h of MCA occlusion were killed at 24 h for measurement of DNA fragmentation by gel electrophoresis. Our data indicate that within a coronal section, DNA fragmentation was present in zero to three cells in each hemisphere of normal and sham-operated rats as well as in the contralateral hemisphere of ischemic rats. The number of cells exhibiting DNA fragmentation increased as early as 0.5 h (8 ± 6), peaked at 24–48 h (213 ± 59), and persisted for 4 weeks (10 ± 2) after onset of reperfusion (p < 0.01). Groups of cells exhibiting DNA fragmentation (>95% neurons) were located primarily in the inner boundary zone of the infarct. With use of gel electrophoresis, purified DNA obtained from the ischemic tissue exhibited the characteristic nucleosome ladder pattern associated with apoptosis. The presence and anatomical location of cells exhibiting DNA fragmentation after transient MCA occlusion suggest that apoptosis contributes to the development of ischemic infarct. In addition, the prolonged presence of DNA fragmentation after the onset of ischemia suggests that apoptotic ischemic brain damage is a dynamic ongoing process.
Lymphocytic Infiltration and Expression of Intercellular Adhesion Molecule-1 in Photochemically Induced Ischemia of the Rat Cortex
Authors: Jander Sebastian , Kraemer Matthias , Schroeter Michael , Witte Otto W. , Stoll Guido
Published: April 2011

The contribution of the immune system to the pathogenesis of ischemic lesions is still uncertain. We have analyzed leukocyte infiltration in photochemically induced focal ischemia of the rat parietal cortex by immunocytochemistry. Between 1 and 2 days after photothrombosis, CD5 + T cells adhered to subpial and cortical vessels and infiltrated the ischemic lesion prior to macrophages. By day 3 numerous T cells and some macrophages, whose number increased further between day 3 and day 7, had infiltrated the border zone around the lesion sparing the center. In addition, CD5–/CD8+ lymphocytes that probably represent natural killer cells were found. Intercellular adhesion molecule-1 (ICAM-1) was expressed on endothelial cells on days 1 and 2 and in the border zone on infiltrating leukocytes from day 3 to day 7. Starting on day 7, macrophages infiltrated the core of the lesion to remove debris. When the entire lesion was covered by macrophages at day 14, the number of T cells had decreased and ICAM-1 immunoreactivity was no longer found in or around the infarct. In conclusion, our study shows that ischemic lesions can lead to a local immune reaction in the CNS. Thus, blocking of lymphocyte-derived cytokines or cell adhesionmolecules may provide a new approach to confining the sequelae of stroke.
Protection against CNS Ischemia by Temporary Interruption of Function-Related Processes of Neurons
Authors: Ames Adelbert , Maynard Kenneth I. , Kaplan Stuart
Published: April 2011

Previous studies have shown that most of the energy consumption of CNS tissue is used for processes that subserve signaling functions of the cells. Since these function-related processes are probably not essential to cell viability, blocking them reversibly with a combination of pharmacologic agents should protect cells from a reduction in energy metabolism. Preliminary experiments to test this hypothesis were performed on isolated rabbit retinas. They were maintained in a newly devised chamber that permitted continuous monitoring of electrophysiological function for ≥8 h. Ischemia was simulated by a 6-fold reduction in both O2 and glucose. This caused a rapid ( t1/2 75 s) and complete loss of the light-evoked response in the optic nerve. Untreated retinas showed full recovery after ½ h of deprivation, but only 50% recovery after 1 h and little or no recovery after 2 or 3 h. Retinas exposed during 3 h of deprivation to a combination of six agents that abolished electrophysiologic function and reduced glucose utilization [tetrodotoxin (TTX), 2-amino-4-phosphonobutyric acid (APB), 2-amino-5-phosphonovaleric acid (APV), amiloride, Mg2+, and Li+] showed full recovery. We conclude that reducing energy requirements by blocking functional processes can prevent ischemic damage.
Cerebrovascular Responses under Controlled and Monitored Physiological Conditions in the Anesthetized Mouse
Authors: Dalkara T. , Irikura K. , Huang Z. , Panahian N. , Moskowitz M. A.
Published: April 2011

Control of physiological parameters such as respiration, blood pressure, and arterial blood gases has been difficult in the mouse due to the lack of technology required to monitor these parameters in small animals. Here we report that anesthetized and artificially ventilated mice can be maintained under physiological control for several hours with apparently normal cerebrovascular reactivity to hypercapnia and mechanical vibrissal stimulation. SV-129 mice were anesthetized with urethane (750 mg/kg i.p.) and α-chloralose (50 mg/kg i.p.), intubated, paralyzed, and artificially ventilated. Respiratory control was maintained within physiological range by reducing the inspiratory phase of the respiratory cycle to <0.1 s and by adjusting end-tidal CO2 to give a Pco2 of 35 ± 3 mm Hg. In these mice, mean arterial pressure (95 ± 9 mm Hg), heart rate (545 ± 78 beats/min), and arterial pH (7.27 ± 0.10) could be maintained for several hours. Body temperature was kept at 36.5–37.5°C. We observed stable regional CBF (rCBF) measurements (as determined by laser–Doppler flowmetry) when systemic arterial blood pressure was varied between 40 and 130 mm Hg. Hypercapnia led to a 38 ± 15% (5% CO2) and 77 ± 34% (10% CO2) increase in rCBF. Mechanical stimulation of contralateral vibrissae for 1 min increased rCBF by 14 ± 4%. Changes in rCBF compare favorably with those observed previously in another rodent species, the Sprague–Dawley rat. After placement of a closed cranial window, cerebrovascular reactivity to hypercapnia and whisker stimulation was intact and well maintained during 2-h superfusion with artificial CSF.
Nicotine Raises the Influx of Permeable Solutes across the Rat Blood—Brain Barrier with Little or No Capillary Recruitment
Authors: Chen J.-L. , Wei L. , Bereczki D. , Hans F.-J. , Otsuka T. , Acuff V. , Ghersi-Egea J.-F. , Patlak C. , Fenstermacher J. D.
Published: April 2011

Nicotine (1.75 mg/kg s.c.) was administered to rats to raise local CBF (lCBF) in various parts of the brain, test the capillary recruitment hypothesis, and determine the effects of this increase in lCBF on local solute uptake by brain. lCBF as well as the local influx rate constants ( K1) and permeability-surface area ( PS) products of [14C]antipyrine and [14C]-3- O-methyl-d-glucose (30MG) were estimated by quantitative autoradiography in 44 brain areas. For this testing, the finding of significantly increased PS products supports the capillary recruitment hypothesis. In 17 of 44 areas, nicotine treatment increased lCBF by 30–150%, K1 of antipyrine by 7–40%, K1 of 30MG by 5–27%, PS product of antipyrine by 0–20% (mean 7%), and PS product of 30MG by 0–23% (mean 8%). Nicotine had no effect on blood flow or influx in the remaining 27 areas. The increases in lCBF and K1 of antipyrine were significant, whereas those in K1 of 30MG and in PS for both antipyrine and 30MG were not statistically significant. The lack of significant changes in PS products implies that in brain areas where nicotine increased blood flow: (a) essentially no additional capillaries were recruited and (b) blood flow within brain capillary beds rises by elevating linear velocity. The K1 results indicate that the flow increase generated by nicotine will greatly raise the influx and washout rates of highly permeable materials, modestly elevate those of moderately permeable substances, and negligibly change those of solutes with extraction fractions of <0.2, thereby preserving the barrier function of the blood–brain barrier.
Functional Increases in Cerebral Blood Volume over Somatosensory Cortex
Authors: Narayan Sanjiv M. , Esfahani Pooneh , Blood Anne J. , Sikkens Lucia , Toga Arthur W.
Published: April 2011

We have examined the relationship between cerebral blood volume (CBV) and electrophysiology over primary somatosensory cortex (S-I) in the rat. We did this by comparing the spatial characteristics and time course of activity-related changes in plasma fluorescence, intrinsic optical reflectance signals, and single unit electrophysiology in S-I to identical stimuli. S-Is of urethane-anesthetized male Sprague–Dawley rats were exposed, and fluorescent Texas Red dextran dye (MW 70,000) was administered intravenously. Subsequently, foredigit electroshock or vibrissal deflection was associated with fluorescence increases over contralateral forelimb or posteromedial barrel subfield cortex. Fluorescence was delayed and prolonged, indicating that CBV increases at 1–1.5 s and peaks 2–2.5 s after the onset of stimulation in both regions. When stimulus intensity was adjusted to produce barely detectable fluorescence foci (10% above background), significant electrophysiologic spiking was seen. At these parameters, fluorescence change overlay areas of increased cortical layer III cell firing on single unit recordings. However, surface boundaries of the smallest observable fluorescence foci at their peak spatial extents consistently overspilled electrophysiologic center receptive fields. Corresponding intrinsic optical reflectance decreases were seen at 610 and 850 nm, exhibiting similar timing and colocalizing closely with fluorescence increase at both wavelengths after identical stimuli. These signals similarly overspilled electrophysiologic activity. Thus, we observed delayed increases in vascular fluorescence (related to CBV) over activated cortex. The smallest detectable fluorescence changes overspilled the center receptive field boundaries and were associated with appreciable electrophysiologic firing. In addition, the striking spatial and temporal similarity between intrinsic optical reflectance and fluorescence activity suggests that changes in intrinsic cortical reflectance are strongly related to changes in CBV.
The Chemistry of the Morita-Baylis-Hillman Reaction
Authors: Shi Min , Wang Feijun , Zhao Mei-Xin , Wei Yin
Published: April 2011

Carbon-carbon bond formations and functional group transformations are the most fundamental reactions for the construction of molecular frameworks and are at the forefront of organic chemistry research. The Morita-Baylis-Hillman (MBH) type reactions possess the two most important requirements - atom economy and generation of multi-functional groups. The last decade has seen exponential growth of the MBH reaction and its applications. In fact, it is already one of the most powerful carbon-carbon bond-forming methods widely used in organic synthesis. Since the 1990s, more and more research groups have initiated work on different aspects of the MBH reaction. These have focused on the scope of the substrates, novel catalysts (especially chiral catalysts), reaction mechanisms, and synthetic applications. Consequently, there is now a need for a reference detailing the chemistry of this important reaction. This unique book summarizes the MBH reaction, aza-MBH reaction and asymmetric MBH/aza-MBH reaction including the latest research and mechanistic investigations. It provides a complete overview of MBH-type reactions aimed at synthetic organic chemists of all levels within academia and industry. The chapters cover the; origin and growth of the Morita-Baylis-Hillman reaction; reactant classes and reaction conditions; catalytic mechanisms; achiral and chiral catalytic systems; transformations of functional groups; use of Morita-Baylis-Hillman adducts and derivatives as starting materials to construct compounds with carbocyclic or heterocyclic frameworks, and the applications of the MBH reaction in synthesizing natural products.
Morita–Baylis–Hillman adducts as effective dipolarophiles in Copper(i)-catalyzed 1,3-dipolar cycloaddition with azomethine ylides: asymmetric construction of pyrrolidine derivatives containing quaternary stereogenic center
Authors: Teng Huai-Long , Huang He , Tao Hai-Yan , Wang Chun-Jiang
Published: April 2011

The first catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides with easily accessible MBH adducts as the dipolarophiles has been developed successfully.
Microwave Hall mobility and electrical properties of electrospun polymer nanofibers
Authors: Babu V. Jagadeesh , Murthy D. V. B. , Subramanian V. , Murthy V. R. K. , Natarajan T. S. , Ramakrishna S.
Published: April 2011

Composite nanofibers from poly(methylmethacrylate)- (PMMA-) conducting polyaniline [PANI(HCl)] were prepared by using the electrospinning technique. The morphology and structural details of the fibers were characterized by SEM and the ac conductivity of the composite fibers found was measured to be ∼ 2.17×10−4 S/cm which is very good enhancement compared to that of pure PMMA and conductivity of PANI-PMMA thin films as well. The conductivity is found to increase with increase in the polyaniline content in the composite. Microwave Hall mobility measurements on electrospun nanofibers showed 17 cm2/V s for the lower loadings. With further increase in the polyaniline content in the composite, the mobility value decreases which is attributed to the increase in carrier-carrier scatterings.
Origin of the colossal dielectric permittivity and magnetocapacitance in LuFe2O4
Authors: Ren P. , Yang Z. , Zhu W. G. , Huan C. H. A. , Wang L.
Published: April 2011

We report the detailed study on the colossal dielectric constant and magnetocapacitance of LuFe2O4. The experimental results indicate that the large dielectric constant of LuFe2O4 is originated from two sources, (1) Maxwell Wagner-type contributions of depletion layers at grain boundaries and the interfaces between sample and contacts, (2) AC response of the constant phase element in the bulk. A detailed equivalent circuit analysis indicates that the conductivity variation can be responsible for the observed “magnetocapacitance.”
Viscosity calculated in simulations of strongly coupled dusty plasmas with gas friction
Authors: Feng Yan , Goree J. , Liu Bin
Published: April 2011

A two-dimensional strongly coupled dusty plasma is modeled using Langevin and frictionless molecular dynamical simulations. The static viscosity η and the wave-number-dependent viscosity η(k) are calculated from the microscopic shear in the random motion of particles. A recently developed method of calculating the wave-number-dependent viscosity η(k) is validated by comparing the results of η(k) from the two simulations. It is also verified that the Green–Kubo relation can still yield an accurate measure of the static viscosity η in the presence of a modest level of friction as in dusty plasma experiments.
Anisotropy of heavy transition metal dopants in Co
Authors: Sharma V. , Manchanda P. , Skomski R. , Sellmyer D. J. , Kashyap A.
Published: April 2011

Evaluating prospects for new transition-metal-rich and lanthanide-free permanent magnets, we calculate the magnetocrystalline anisotropy of dilute Co1−xPtx and Co1−xPdx alloys. The ab initio calculations are done by using the full-potential linear augmented plane wave method, treating exchange and correlation within the generalized gradient approximation. The anisotropy contributions, 11.9 kJ/m3 per at. % Pd and 10.8 kJ/m3 per at. % Pt, are in a range suitable for permanent magnets application.
Oblique-incidence sputtering of Ru intermediate layer for decoupling of intergranular exchange in perpendicular recording media
Authors: Saito Shin , Inoue Ken , Takahashi Migaku
Published: April 2011

During the Ru deposition process for granular type perpendicular magnetic recording media, both a reduction in the Ru intermediate layer thickness and lowering of sputtering gas pressure were successfully achieved by focusing on a self-shadowing effect. Oblique-incidence sputtering with a 60° incident angle under an Ar gas pressure of 0.6 Pa yielded (1) columnar Ru grains with a growth direction of 30° from the film normal, (2) c-plane sheet texture by epitaxial growth on the Pt underlayer, and (3) a flat envelope of the surface and a deep gap at grain boundaries. This change in the Ru structure significantly contributes to reducing exchange coupling among magnetic grains, especially in the initial growth region in an overlying granular medium.
Magnetizing reversal in multilayer hard–soft composites SmCo5–FeCo
Authors: Belemuk A. M. , Chui S. T.
Published: April 2011

We studied the demagnetization curves and the energy product of multilayers of hard (SmCo5) and soft (FeCo) magnetic material with finite temperature Monte Carlo simulation. Different from previous studies, the easy axis of the hard phase is perpendicular to the layers, as is discovered experimentally. We perform simulations with and without the dipolar interaction and find a significant difference in the coercive field and the energy product at high temperatures.
Effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7–xGex ribbons
Authors: Hsieh C. C. , Chang H. W. , Zhao X. G. , Sun A. C. , Chang W. C.
Published: April 2011

The effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7–xGex (x = 0–0.8) ribbons have been investigated. SmCo7–xGex ribbons (x = 0–0.6) spun at a high wheel speed of 40 m/s crystallize in the TbCu7-type structure. The x-ray diffraction results analyzed by the Rietveld refinement method show that Ge prefers to occupy the 2e sites in the TbCu7-type structure. The grain size of the ribbons is only slightly decreased with the proper amount of Ge substitution (x < 0.7). When increasing x from 0–0.6, the coercivity of the SmCo7–xGex ribbons is enhanced from 1.9 kOe for binary SmCo7 to 7.5 kOe for SmCo6.5Ge0.5 which is mainly due to the enhancement of the magnetic anisotropy field by the Ge substitution for Co in 2e sites. Furthermore, a slight addition of carbon in the alloy is effective in refining the grain size and further improving the coercivity of the ribbons. Coercivity as high as 11.4 kOe could be obtained for SmCo6.7Ge0.3C0.1 ribbons.
Preparation and magnetic properties of bulk nanostructured PrCo5 permanent magnets with strong magnetic anisotropy
Authors: Liu W. Q. , Zuo J. H. , Yue M. , Lv W. C. , Zhang D. T. , Zhang J. X.
Published: April 2011

Bulk anisotropic PrCo5 nanostructured magnets were prepared by hot deformation technique. The effects of height reduction on the structure and magnetic properties of the magnets were studied. It is found that the height reduction plays an important role in the formation of c-axis crystal texture of PrCo5 phase during hot deformation process. With the increase of height reduction, the c-axis crystal texture becomes more and more dominant, indicating strong magnetic anisotropy in the magnets. As a result, the saturated magnetization (Ms) of the magnets increases gradually, while the coercivity (Hci) of the magnets drops simultaneously, resulting in the remanence (Mr) of the magnets rising first, peaking at 80% height reduction, then dropping again. Under optimal height reduction of 80%, the PrCo5 magnet bears magnetic properties of Ms of 1.00 T, Mr of 0.86 T, Hci of 488.5 kA/m, and (BH)max of 96.87 kJ/m3.
Analysis of the National Ignition Facility ignition hohlraum energetics experiments
Authors: Town R. P. J. , Rosen M. D. , Michel P. A. , Divol L. , Moody J. D. , Kyrala G. A. , Schneider M. B. , Kline J. L. , Thomas C. A. , Milovich J. L. , Callahan D. A. , Meezan N. B. , Hinkel D. E. , Williams E. A. , Berger R. L. , Edwards M. J. , Suter L. J. , Haan S. W. , Lindl J. D. , Dewald E. L. , Dixit S. , Glenzer S. H. , Landen O. L. , Moses E. I. , Scott H. A. , Harte J. A. , Zimmerman G. B.
Published: April 2011

A series of 40 experiments on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)] to study energy balance and implosion symmetry in reduced- and full-scale ignition hohlraums was shot at energies up to 1.3 MJ. This paper reports the findings of the analysis of the ensemble of experimental data obtained that has produced an improved model for simulating ignition hohlraums. Last year the first observation in a NIF hohlraum of energy transfer between cones of beams as a function of wavelength shift between those cones was reported [P. Michel et al., Phys. Plasmas 17, 056305 (2010)]. Detailed analysis of hohlraum wall emission as measured through the laser entrance hole (LEH) has allowed the amount of energy transferred versus wavelength shift to be quantified. The change in outer beam brightness is found to be quantitatively consistent with LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2, 51 (1975)] simulations using the predicted energy transfer when possible saturation of the plasma wave mediating the transfer is included. The effect of the predicted energy transfer on implosion symmetry is also found to be in good agreement with gated x-ray framing camera images. Hohlraum energy balance, as measured by x-ray power escaping the LEH, is quantitatively consistent with revised estimates of backscatter and incident laser energy combined with a more rigorous non-local-thermodynamic-equilibrium atomic physics model with greater emissivity than the simpler average-atom model used in the original design of NIF targets.
Analysis of write-head synchronization and adjacent track erasure in bit patterned media using a statistical model
Authors: Kalezhi Josephat , Miles Jim J.
Published: April 2011

An analysis of the performance of a bit patterned media data storage system composed of nanoscale islands with variations in position and magnetic properties has been carried out. The statistical model of write errors includes adjacent track erasure and error rates are computed according to the down-track synchronization of the write head switching position and cross-track head position variations. Two-dimensional maps of bit error rates reveal that distributions of position and anisotropy have a severe impact on the performance of the system. Results show that head field cross-track gradients needs to be tightly controlled to minimize the effects of adjacent track erasure.
Novel magnetophotonic crystals controlled by the electro-optic effect for non-reciprocal high-speed modulators
Authors: Goto Taichi , Sato Hiroshi , Takagi Hiroyuki , Baryshev Alexander V. , Inoue Mitsuteru
Published: April 2011

We present a new type of electro- and magneto-optical spatial light modulators (e-MOSLMs) utilizing the concept of photonic crystals (PCs) – such e-MOSLMs have a microcavity structure. They comprise a magneto-optical (MO) and electro-optical (EO) constituents that can control the direction of the polarization plane, when applying voltage and/or external magnetic fields. Optical spectra of e-MOSLMs were analyzed by using the matrix approach. Calculations showed that e-MOSLMs can change the direction of polarization over a considerably large range of angles at relatively low power consumption and with no significant change of the light intensity.
Spin glass behavior in Sr2Mn0.7Fe0.3MoO6
Authors: Wang Xianjie , Sui Yu , Li Yao , Xu Miao , Wang Wendong , Liu Pan , Tang Jinke
Published: April 2011

In this paper, we present a detailed study of the dc magnetization, ac susceptibility and aging effect in a polycrystalline Sr2Mn0.7Fe0.3MoO6 sample. Based on the tetragonal I 4/m space group, the XRD pattern is well refined, which shows that the sample is crystallized in a single phase double-perovskite structure without impurity phase. The dc magnetization, ac susceptibility, heat capacity, aging experiments and fitting results show the existence of the spin glass behavior in the sample. The spin glass behavior originates from the competition between the ferromagnetic and antiferromagnetic couplings due to the magnetic frustration at the interface of ferromagnetic and antiferromagnetic clusters in the phase separate sample.
Magnetization reversal mechanism of Nd-Fe-B films with perpendicular magnetic anisotropy
Authors: Liu Xiaoxi , Ishida Go , Morisako Akimitsu
Published: April 2011

The microstructure and magnetic properties of Nd-Fe-B films with thicknesses from 100 nm to 3 nm have been investigated. All the films show excellent perpendicular magnetic anisotropy with a squareness ratio of 1 in the perpendicular direction and almost zero coercivity in the in-plane direction. Of particular interest is that the initial magnetization curves sensitively depended on the film thickness. Films thicker than 15 nm show steep initial magnetization curve. Although the films have coercivities larger than 21 kOe, the films can be fully magnetized from the thermally demagnetized state with a field as small as 5 kOe. With the decrease of film thickness to 5 nm, the initial magnetization curve becomes flat. The evolution of initial magnetization curves with film thickness can be understood by the microstructure of the films. Films with thickness of 15 nm show close-packed grains without any intergranular phases. Such microstructures lead to steep initial magnetization curves. On the other hand, when the film thickness decreased to 3 nm, the film thickness became nonuniform. Such microstructure leads to flat initial magnetization curves.
Temperature dependence of magnetic anisotropy constant in manganese ferrite nanoparticles at low temperature
Authors: Yoon Sunghyun , Krishnan Kannan M.
Published: April 2011

The temperature dependence of the effective magnetic anisotropy constant, K(T), of MnFe2O4 nanoparticles is obtained based on superconducting quantum interference device magnetometry measurements. The variation of the blocking temperature, TB, as a function of particle radius, r, is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and TB. The resultant effective magnetic anisotropy constant K(T) decreases markedly with increasing temperature from 8.5 × 104 J/m3 at 5 K to 0.35 × 104 J/m3 at 125 K.
Magnetostriction “drop” in 〈110〉 oriented polycrystals Tb0.36Dy0.64(Fe0.85Co0.15)2 after transverse field annealing
Authors: Zhang Changsheng , Ma Tianyu , Yan Mi
Published: April 2011

A 〈110〉 oriented polycrystal Tb0.36Dy0.64(Fe0.85Co0.15)2 was subjected to annealing in a transverse field of 240 kA/m. Axial magnetostrictions (defined as λ∥) of the magnetically annealed specimen were investigated in fields applied at a series of angles θ away from its axis. For the untreated specimen, at the angle θ scope from 30° to 60°, λ∥ increases to a maximum and then drops gradually during magnetization processes. After magnetic annealing, however, the magnetostriction “drop” behavior occurs at a narrower θ range from 40° to 60°. In addition, at these magnetization directions where drop occurs, λ∥ is negative for the magnetically annealed specimen, whereas it keeps positive for the untreated one. The value of “dropped” magnetostriction (defined as |Δλ∥,d|) increases with the increase of θ for the untreated specimen, but decreases for the magnetically annealed one. Based on a single-{111}-twin crystal growth model, magnetic domain rotation paths are simulated to explain the differential magnetostriction drop behavior.
Effective excitation by single magnet in rotation sensor and domain wall displacement of FeCoV wire
Authors: Kohara Takashi , Yamada Tsutomu , Abe Susumu , Kohno Shiro , Kaneko Fumio , Takemura Yasushi
Published: April 2011

Recently, a sensor structure consisting of magnetic wires attached directly to a rotating shaft, a pick-up coil, and a pair of magnets separately located outside the rotor was proposed. This paper presents a structure whose excitation source is just a single magnet. This structure decreases the cost of the previous sensor while retaining its advantages. For example, multiple output signals can be obtained per turn of the shaft by simply adding a corresponding number of wires, without requiring more pick-up coils and magnet pairs. In this study, the dependence of the output voltage on the pick-up coil was measured and the domain wall structure was elucidated by the measurement result.
Effect of initial stress/strain state on formation of (001) preferred orientation in L1 FePt thin films
Authors: Mei J. K. , Yuan F. T. , Liao W. M. , Yao Y. D. , Lin H. M. , Lee H. Y. , Hsu J. H.
Published: April 2011

The stress state of FePt thin films deposited at room temperature was controlled within the range from 1.01 GPa compressive to 0.18 GPa tensile before taking rapid thermal annealing (RTA). After the order–disorder transformation triggered by RTA at temperatures (Ta) from 650 to 800 °C for 5 min, the tensile-stressed films exhibit significant preferred orientation of (001) of L10 structure. However, the compressive-strained ones show isotropic texture. Strong (001) texture with high Lotgering orientation factor of 0.9 is obtained at Ta = 800 °C, resulting in enhanced perpendicular magnetic anisotropy. The results provide direct evidence of stress-induced (001) texture, which could be significant for future applications.
Direct determination of the band alignment at the (Zn,Mg)O/CISSe interface
Authors: Erfurth F. , Grimm A. , Palm J. , Niesen T. P. , Reinert F. , Weinhardt L. , Umbach E.
Published: April 2011

The electronic and chemical properties of the (Zn1−x,Mgx)O/CuIn(S,Se)2 interface, prepared by sputtering of thin (Zn,Mg)O layers, were investigated with direct and inverse photoelectron spectroscopy on in situ prepared samples. With the combination of both techniques we have determined the band alignment at this interface as a function of Mg-content in the range 0≤x≤0.30. We find that the band alignment at the interface can be tailored between a “cliff” (downward step) in the conduction band for pure ZnO and a “spike” (upward step) for high Mg-contents. A direct influence of the band alignment modifications on the solar cell parameters is found.
Magnetic wormhole solutions in Einstein–Gauss–Bonnet gravity with power Maxwell invariant source
Authors: Hendi S. H.
Published: April 2011

In this paper, we consider the Einstein–Gauss–Bonnet gravity in the presence of power Maxwell invariant field and present a class of rotating magnetic solutions. These solutions are nonsingular and horizonless, and satisfy the so-called flare-out condition at r = r+ and may be interpreted as traversable wormhole near r = r+. In order to have a vanishing electromagnetic field at spatial infinity, we restrict the nonlinearity parameter to s > 1/2. Investigation of the energy conditions shows that these solutions satisfy the null, week, and strong energy conditions simultaneously for s > 1/2, which means that there is no exotic matter near the throat. We also calculate the conserved quantities of the wormhole such as mass, angular momentum, and electric charge density, and show that the electric charge depends on the rotation parameters and the static wormhole does not have a net electric charge density. In addition, we show that for s = (n + 1)/4, the energy–momentum tensor is traceless and the solutions are conformally invariant, in which the expression of the Maxwell field does not depend on the dimensions and its value coincides with the Reissner–Nordström solution in four dimensions. Finally, we produce higher dimensional BTZ-like wormhole solutions for s = n/2, in which in this case the electromagnetic field Fψr∝r−1.
Spectral coupling of fluorescent solar concentrators to plasmonic solar cells
Authors: Wang Shu-Yi , Borca-Tasciuc Diana-Andra , Kaminski Deborah A.
Published: April 2011

Coupling luminescent solar concentrators (LSC) with plasmonic solar cells is a potential method to increase conversion efficiency while reducing cost associated with large-area photovoltaic and solar-tracking systems. Specifically, the emission spectrum of the fluorescent dye in the LSC can be matched to the absorption spectrum in the photovoltaic cell which can be tuned by surface plasmon resonance. Here we investigate this concept employing organic solar cells with plasmonic silver nanoparticles and polymethylmethacrylate-based solar concentrators with Lumogen Red dye. The absorption enhancement is predicted by Mie theory, taking size effect on dielectric properties into consideration. A factor of two increase of conversion efficiency is obtained when the absorption peak in the solar cell is tuned to match the emission peak of Lumogen Red dye. A similar approach could be employed to enhance the efficiency of other LSC-photovoltaic systems including those based on silicon solar cells with different surface plasmonic nanostructures.
Angled long tip to tuning fork probes for atomic force microscopy in various environments
Authors: Higuchi Seiji , Kuramochi Hiromi , Kubo Osamu , Masuda Shintaro , Shingaya Yoshitaka , Aono Masakazu , Nakayama Tomonobu
Published: April 2011

We expand the range of applications of a tuning fork probe (TFP) in frequency-modulation atomic force microscopy (FM-AFM) by attaching a long metal tip at a certain angle. By the combined flexure of the metal tip and the tuning fork prong, this TFP can change the direction of the detectable force by switching the resonance frequency, which has not been realized with conventional TFPs with short tips. The oscillatory behavior of the tip apex of the TFP is predicted by computer simulations and is experimentally confirmed with scanning electron microscope. FM-AFM operations using this TFP are performed in various environments, i.e., in ultrahigh vacuum, air, and water. FM-AFM images obtained at an atomic step of highly oriented pyrolytic graphite in air show a clear difference depending on the excitation frequency. It is also revealed that the higher order flexural modes of this TFP are advantageous for FM-AFM in water due to the reduction in the degree of hydrodynamic damping.
An apparatus for in situ spectroscopy of radiation damage of polymers by bombardment with high-energy heavy ions
Authors: Baake Olaf , Seidl Tim , Hossain Umme Habiba , Delgado Adriana O. , Bender Markus , Severin Daniel , Ensinger Wolfgang
Published: April 2011

A new target station providing Fourier transform infrared (FT-IR) spectroscopy and residual gas analysis (RGA) for in situ observation of ion-induced changes in polymers has been installed at the GSI Helmholtz Centre for Heavy Ion Research. The installations as well as first in situ measurements at room temperature are presented here. A foil of polyimide Kapton HN® was irradiated with 1.1 GeV Au ions. During irradiation several in situ FT-IR spectra were recorded. Simultaneously outgassing degradation products were detected with the RGA. In the IR spectra nearly all bands decrease due to the degradation of the molecular structure. In the region from 3000 to 2700 cm−1 vibration bands of saturated hydrocarbons not reported in literature so far became visible. The outgassing experiments show a mixture of C2H4, CO, and N2 as the main outgassing components of polyimide. The ability to combine both analytical methods and the opportunity to measure a whole fluence series within a single experiment show the efficiency of the new setup.
Asymptotic iteration technique for second-order dynamic equations on time scales
Authors: Misir Adil , Ogrekci Suleyman
Published: April 2011

An asymptotic iteration method for solving second-order homogeneous linear dynamic equation of the form y△△ = a0(t)y△ + b0(t)y is introduced. Where a0(t) and b0(t) are \documentclass[12pt]{minimal}\begin{document}$C_{rd}^{m}( \mathbb {T} )$\end{document}Crdm(T) functions and the positive integer m depends on the differentiability of a0(t), b0(t) and iteration steps.
SU(6)⊃SU(3)⊗SU(2) and SU(8)⊃SU(4)⊗SU(2) Clebsch–Gordan coefficients
Authors: Garcia-Recio C. , Salcedo L. L.
Published: April 2011

Tables of scalar factors are presented for \documentclass[12pt]{minimal}\begin{document}$\mathbf {63}\otimes \mathbf {63}$\end{document}63⊗63 and \documentclass[12pt]{minimal}\begin{document}$\mathbf {120}\otimes \mathbf {63}$\end{document}120⊗63 in SU(8)⊃SU(4)⊗SU(2), and for \documentclass[12pt]{minimal}\begin{document}$\mathbf {35}\otimes \mathbf {35}$\end{document}35⊗35 and \documentclass[12pt]{minimal}\begin{document}$\mathbf {56}\otimes \mathbf {35}$\end{document}56⊗35 in SU(6)⊃SU(3)⊗SU(2). Related tables for SU(4)⊃SU(3)⊗U(1) and SU(3)⊃SU(2)⊗U(1) are also provided so that the Clebsch–Gordan coefficients can be completely reconstructed. These are suitable to study meson–meson and baryon–meson interactions within a spin-flavor symmetric scheme.
Average dynamics of a driven set of globally coupled excitable units
Authors: Alonso Leandro M. , Mindlin Gabriel B.
Published: April 2011

We investigate the behavior of the order parameter describing the collective dynamics of a large set of driven, globally coupled excitable units. We derive conditions on the parameters of the system that allow to bound the degree of synchrony of its solutions. We describe a regime where time dependent nonsynchronous dynamics occurs and, yet, the average activity displays low dimensional, temporally complex behavior.
Ohmic contact between ZnO and Pt by InSb layer in a ZnO Schottky diode
Authors: Jee Seung Hyun , Kakati Nitul , Lee Seok Hee , Yoon Hyon Hee , Yoon Young Soo
Published: April 2011

The surface of the ZnO thin films was modified by a thin InSb layer by using a thermal evaporator to increase the work function without altering the physical properties of the film. We expected that the InSb thin layer with a high work function could achieve the Ohmic contact between the ZnO and Pt electrodes by reducing an energy barrier due to increase in the ZnO thin film. The Ohmic contact was achieved in the interface between the ZnO and Pt electrodes by the InSb thin layer.
Spontaneous polarization estimation from the soft mode in strain-free epitaxial polar axis-oriented Pb(Zr,Ti)O3 thick films with tetragonal symmetry
Authors: Ehara Yoshitaka , Utsugi Satoru , Nakajima Mitsumasa , Yamada Tomoaki , Iijima Takashi , Taniguchi Hiroki , Itoh Mitsuru , Funakubo Hiroshi
Published: April 2011

The ferroelectric property, crystal structure, and A1(1TO) soft mode of almost strain-free epitaxial polar axis-oriented tetragonal lead zirconate titanate thick films grown on CaF2 substrates were investigated by changing the Zr/(Zr+Ti) ratio and the temperature. The square of spontaneous polarization (Ps), Ps2, monotonically increased as tetragonal distortion, (c/a)−1, increased where a and c are the lattice parameters of the films and as the square of frequency in A1(1TO), ω2[A1(1TO)], increased. Additionally, the relationships of Ps2, (c/a−1), and ω2[A1(1TO)] were experimentally obtained, which confirmed the Ps value obtained from (c/a−1) and ω[A1(1TO)] without direct polarization measurements.
Real time achromatic measurement of space-variant polarizations
Authors: Fridman Moti , Grinvald Eran , Godel Amit , Nixon Micha , Friesem Asher A. , Davidson Nir
Published: April 2011

A compact configuration for real-time achromatic measurements of space-variant light polarization is presented. The experimental results reveal that the full state of polarization at each location within a light beam or at each wavelength can be obtained with accuracy of over π/18.
Structural and magnetic properties of bulk nanocrystalline Erbium metal
Authors: Yue Ming , Huang Jun , Liu Weiqiang , Zhang Dongtao , Zhang Jiuxing
Published: April 2011

Bulk nanocrystalline Erbium metals were prepared via Spark Plasma Sintering (SPS) and subsequent annealing process. The nanocrystalline Er metals have the same hexagonal close packed structure as that of coarse-grained sample. Decrease in grain size results in remarkable changes in the three magnetic ordering temperatures of the nanocrystalline Er metal. At 5 K, the magnetization drops by 10.9%, while the coercivity increases by 4 times for nanocrystalline Er compared with those of coarse-grained sample. These results indicate the remarkable influence of the nanostructure on the magnetism of Er due to finite size effect.
Room temperature ferromagnetism in pure and Co- and Fe-doped CeO2 dilute magnetic oxide: effect of oxygen vacancies and cation valence
Authors: Singhal R K , Kumari P , Kumar Sudhish , Dolia S N , Xing Y T , Alzamora M , Deshpande U P , Shripathi T , Saitovitch Elisa
Published: April 2011

The evolution of reversible room temperature ferromagnetism (RTFM) has been investigated in Co- and Fe-doped (5% each) and non-doped CeO2 polycrystalline samples. Specimens with different oxygen vacancy (VO) concentration including the (i) as-synthesized, (ii) hydrogenated and (iii) re-annealed in air were investigated using SQUID magnetometry, x-ray diffraction and x-ray photoelectron spectroscopy. The influence of the electronic properties on the RTFM was examined/analysed systematically. Our findings confirm that the ferromagnetism observed in CeO2 originates due to the oxygen vacancies, supporting the VO mediated ferromagnetic exchange mechanism. Additionally, the cationic (cerium and transition metal) valence states play a crucial role.
A phosphor-free white light-emitting diode using In2O3 : Tb transparent conductive light converter
Authors: Chen Lung-Chien , Tien Ching-Ho , Liao Wei-Chian
Published: April 2011

Tb-doped indium oxide (In2O3 : Tb) films were deposited on a GaN-based near-ultraviolet (NUV) light-emitting diode (LED) as a transparent conductive light converter to form a white LED. The transmittance of the In2O3 : Tb film (Tb at 10 wt%) exceeded 80% in visible light and the resistivity was 0.325 Ω cm. The In2O3 : Tb transparent conductive light converter was also employed on GaN-based LEDs. GaN-based NUV-LEDs with In2O3 : Tb film (Tb at 10 wt%) produced forward biases of 3.42 V at an injection current of 20 mA. With increasing temperature, increasing Tb3+ concentration and increasing injection current from 20 to 100 mA, the chromaticity coordinates barely changed in the white light area. Therefore, the GaN-based NUV-LED with In2O3 : Tb film had a stable white light colour, when temperature and injection current changed, and is suitable for solid-state lighting.