bluuebunny/crossref_metadata_2025 huggingface dataset:
Emission spectroscopy of clay minerals and evidence for poorly crystalline aluminosilicates on Mars from Thermal Emission Spectrometer data
Authors: Michalski Joseph R. , Kraft Michael D. , Sharp Thomas G. , Williams Lynda B. , Christensen Philip R.
Published: March 2006

To understand the aqueous history of Mars, it is critical to constrain the alteration mineralogy of the Martian surface. Previously published analyses of thermal infrared (λ = 6–25 μm) remote sensing data of Mars suggest that dark regions have ∼15–20% clay minerals. However, near‐infrared (λ = 1–3 μm) spectral results generally do not identify widespread clay minerals. Thermal infrared detections of clays on Mars are difficult to interpret owing in part to the relative paucity of published spectral analyses of clay minerals and clay‐bearing materials using similar spectra (thermal infrared emission spectra). In this study, we present an analysis of the thermal emission spectral features (λ = ∼6–25 μm or 400–1650 cm−1) of a suite of clay mineral reference materials and clay‐bearing rocks, linking their spectral features to the crystal chemical properties of the clays. On the basis of this context provided by the emission spectral analysis of clay minerals and clay‐bearing rocks, we reconsider the evidence for clay minerals on Mars from Thermal Emission Spectrometer (TES) results. We propose that global‐scale clay abundances determined from TES probably represent a geologically significant surface component, though they may actually correspond to poorly crystalline aluminosilicates with similar Si/O ratios to clay minerals (0.3–0.4), rather than well‐crystalline clays. If clay minerals or clay‐like materials on Mars are poorly crystalline and/or dessicated, they may be detectable in the thermal infrared, but not easily detected with near‐infrared data sets.
Effect of ocean gateways on the global ocean circulation in the late Oligocene and early Miocene
Authors: von der Heydt Anna , Dijkstra Henk A.
Published: March 2006

We investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns. Using a fully coupled climate model in an idealized setup, we compare situations corresponding to the late Oligocene, the early Miocene, and present day. The model results show the existence of a flow reversal through the Panama Seaway between the Oligocene and Miocene. This flow reversal is induced by global tectonic changes related to the widening of the Southern Ocean passages and the closing of the Tethys Seaway. It mainly involves the wind‐driven ocean circulation, in agreement with previous model studies. The global thermohaline circulation in the Oligocene and Miocene simulations is significantly different from the present‐day conveyor circulation, as there is deepwater formation in both the North Atlantic and the North Pacific oceans. In particular, in the Oligocene simulation the salinity contrast between the Atlantic and Pacific oceans is reduced because of water mass exchange through the low‐latitude connections between the two oceans.
Inverse modeling of multimodal conductivity distributions
Authors: Janssen Gijs M. C. M. , Valstar Johan R. , van der Zee Sjoerd E. A. T. M.
Published: March 2006

We present a method for the calibration of multimodal hydraulic conductivity distributions and apply this method to the particular case of confining layers with a complex geological architecture. The basis of our technique is the transformation of the original multimodal conductivity distribution to the standard normal distribution, thus fulfilling the condition of normality which is required by the used representer‐based inverse algorithm (Valstar et al., 2004). Using this transformation, a calibration that starts from a homogeneous prior field is shown to radically improve the estimation of the protective properties of the confining layer compared to a unimodal approach to the calibration. The method is also used for the calibration of multimodal heterogeneous prior fields. The inevitable distortion of the original parameter covariances in the posterior fields that results from the transformation process is absorbed by an iterative postprocessing procedure, in which lithologic information obtained from the distorted calibrated fields is used to condition the generation of a new multimodal field that complies again with the original geostatistics. After transformation, this new field can be calibrated again, and this process is repeated until the newly generated field agrees with the measurement information sufficiently well. Then, the lithologic distribution of this new field is fixed, and the intrafacies conductivity distributions are calibrated. This approach is shown to preserve the original geostatistics, both of the lithology field and of the intralithology hydraulic conductivity distributions.
Introduction to special section on Hydrologic Synthesis
Authors: Hubbard Susan , Hornberger George
Published: March 2006

The Hydrological Synthesis special section presents synthesis topics that have the potential to revolutionize hydrological sciences in a manner needed to meet critical water challenges that we now face. The special section also highlights topics that are important and exciting enough to compel researchers to engage in collaborative synthesis activities. This introductory paper provides a brief overview of nine papers that are included in this special section, which discuss the synthesis of tools, data, concepts, theories, or approaches across disciplines and scales. The wide range of topics that are explored include groundwater quality, river restoration, water management, nitrogen cycling, and Earth surface dynamics. Collectively, the special section papers illustrate that the challenge to deal effectively with complex water problems is not purely a scientific, technological, or socioeconomic one; it is instead a complex, 21st century problem that requires coordinated synthesis.
Cortical Glutamate Metabolism is Enhanced in a Genetic Model of Absence Epilepsy
Authors: Melø Torun M , Sonnewald Ursula , Touret Monique , Nehlig Astrid
Published: March 2006

Disturbances in GABAergic and glutamatergic neurotransmission in the thalamocortical loop are involved in absence seizures. Here, we examined potential disturbances in metabolism and interactions between neurons and glia in 5-month-old genetic absence epilepsy rats from Strasbourg (GAERS) and nonepileptic rats (NER). Animals received [1-13C]glucose and [1,2-13C]acetate, the preferential substrates of neurons and astrocytes, respectively. Extracts from cerebral cortex, thalamus, and hippocampus were analyzed by 13C nuclear magnetic resonance spectroscopy. Most changes were detected in the cortex. Pyruvate metabolism was enhanced as evidenced by increases of lactate, and labeled and unlabeled alanine. Neuronal mitochondrial metabolism was also enhanced as detected by elevated amounts of N-acetylaspartate and nicotinamide adenine dinucleotide as well as increased incorporation of label from [2-13C]acetyl CoA into glutamate, glutamine, and aspartate. Likewise, mitochondrial metabolism in astrocytes was increased. Changes in thalamus were restricted to increased concentration and labeling of glutamine. Changes in the hippocampus were similar to those in the cortex. This increase in glutamate-glutamine metabolism in cortical neurons and astrocytes accompanied by a decreased gamma aminobyturic acid level may lead to impaired thalamic filter function. Hence, reduced sensory input to cortex could allow the occurrence of spike-and-wave discharges in the thalamocortical loop. Increased glutamatergic output from the cortex to hippocampus may be the underlying cause of improved learning in GAERS.
Up-regulation of the clusterin gene after proteotoxic stress: implication of HSF1–HSF2 heterocomplexes
Authors: Loison Fabien , Debure Laure , Nizard Philippe , le Goff Pascale , Michel Denis , le Dréan Yves
Published: March 2006

Clusterin is a secreted protein chaperone up-regulated in several pathologies, including cancer and neurodegenerative diseases. The present study shows that accumulation of aberrant proteins, caused by the proteasome inhibitor MG132 or the incorporation of the amino acid analogue AZC (L-azetidine-2-carboxylic acid), increased both clusterin protein and mRNA levels in the human glial cell line U-251 MG. Consistently, MG132 treatment was capable of stimulating a 1.3 kb clusterin gene promoter. Promoter deletion and mutation studies revealed a critical MG132-responsive region between −218 and −106 bp, which contains a particular heat-shock element, named CLE for ‘clusterin element’. Gel mobility-shift assays demonstrated that MG132 and AZC treatments induced the formation of a protein complex that bound to CLE. As shown by supershift and chromatin-immunoprecipitation experiments, CLE is bound by HSF1 (heat-shock factor 1) and HSF2 upon proteasome inhibition. Furthermore, co-immunoprecipitation assays indicated that these two transcription factors interact. Gel-filtration analyses revealed that the HSF1–HSF2 heterocomplexes bound to CLE after proteasome inhibition have the same apparent mass as HSF1 homotrimers after heat shock, suggesting that HSF1 and HSF2 could heterotrimerize. Therefore these studies indicate that the clusterin is a good candidate to be part of a cellular defence mechanism against neurodegenerative diseases associated with misfolded protein accumulation or decrease in proteasome activity.
Chelation and determination of labile iron in primary hepatocytes by pyridinone fluorescent probes
Authors: Ma Yongmin , de Groot Herbert , Liu Zudong , Hider Robert C. , Petrat Frank
Published: March 2006

A series of fluorescent iron chelators has been synthesized such that a fluorescent function is covalently linked to a 3-hydroxypyridin-4-one. In the present study, the fluorescent iron chelators were loaded into isolated rat hepatocytes. The intracellular fluorescence was not only quenched by an addition of a highly lipophilic 8-hydroxyquinoline–iron(III) complex but also was dequenched by the addition of an excess of the membrane-permeable iron chelator CP94 (1,2-diethyl-3-hydroxypyridin-4-one). The time course of uptake of iron and iron chelation in single, intact cells was recorded on-line by using digital fluorescence microscopy. Intracellular concentrations of various fluorescent iron chelators were determined by using a spectrofluorophotometer subsequent to lysis of probe-loaded cells and were found to depend on their partition coefficients; the more hydrophobic the compound, the higher the intracellular concentration. An ex situ calibration method was used to determine the chelatable iron pool of cultured rat hepatocytes. CP655 (7-diethylamino-N-[(5-hydroxy-6-methyl-4-oxo-1,4-dihydropyridin-3-yl)methyl]-N-methyl-2-oxo-2H-chromen-3-carboxamide), which is a moderately lipophilic fluorescent chelator, was found to be the most sensitive probe for monitoring chelatable iron, as determined by the intracellular fluorescence increase induced by the addition of CP94. The concentration of the intracellular chelatable iron pool in hepatocytes was determined by this probe to be 5.4±1.3 μM.
Bax translocates to mitochondria of heart cells during simulated ischaemia: involvement of AMP-activated and p38 mitogen-activated protein kinases
Authors: Capano Michela , Crompton Martin
Published: March 2006

The cytosolic protein Bax plays a key role in apoptosis by migrating to mitochondria and releasing proapoptotic proteins from the mitochondrial intermembrane space. The present study investigates the movement of Bax in isolated rat neonatal cardiomyocytes subjected to simulated ischaemia (minus glucose, plus cyanide), using green fluorescent protein-tagged Bax as a means of imaging Bax movements. Simulated ischaemia induced Bax translocation from the cytosol to mitochondria, commencing within 20 min of simulated ischaemia and progressing for several hours. Under the same conditions, there was an increase in the active, phosphorylated forms of p38 MAPK (mitogen-activated protein kinase) and AMPK (AMP-activated protein kinase). The AMPK activators AICAR (5-aminoimidazole-4-carboxamide ribonucleoside) and metformin also stimulated Bax translocation. Inhibition of p38 MAPK with SB203580 attenuated the phosphorylation of the downstream substrates, MAPK-activated protein kinases 2 and 3, but not that of the upstream MAPK kinase 3, nor of AMPK. Under all conditions (ischaemia, AICAR and metformin), SB203580 blocked Bax translocation completely. It is concluded that Bax translocation to mitochondria is an early step in ischaemia and that it occurs in response to activation of p38 MAPK downstream of AMPK.
Heterologous production in Wolinella succinogenes and characterization of the quinol:fumarate reductase enzymes from Helicobacter pylori and Campylobacter jejuni
Authors: Mileni Mauro , MacMillan Fraser , Tziatzios Christos , Zwicker Klaus , Haas Alexander H. , Mäntele Werner , Simon Jörg , Lancaster C. Roy D.
Published: March 2006

The ϵ-proteobacteria Helicobacter pylori and Campylobacter jejuni are both human pathogens. They colonize mucosal surfaces causing severe diseases. The membrane protein complex QFR (quinol:fumarate reductase) from H. pylori has previously been established as a potential drug target, and the same is likely for the QFR from C. jejuni. In the present paper, we describe the cloning of the QFR operons from the two pathogenic bacteria H. pylori and C. jejuni and their expression in Wolinella succinogenes, a non-pathogenic ϵ-proteobacterium. To our knowledge, this is the first documentation of heterologous membrane protein production in W. succinogenes. We demonstrate that the replacement of the homologous enzyme from W. succinogenes with the heterologous enzymes yields mutants where fumarate respiration is fully functional. We have isolated and characterized the heterologous QFR enzymes. The high quality of the enzyme preparation enabled us to determine unequivocally by analytical ultracentrifugation the homodimeric state of the three detergent-solubilized heterotrimeric QFR enzymes, to accurately determine the different oxidation–reduction (‘redox’) midpoint potentials of the six prosthetic groups, the Michaelis constants for the quinol substrate, maximal enzymatic activities and the characterization of three different anti-helminths previously suggested to be inhibitors of the QFR enzymes from H. pylori and C. jejuni. This characterization allows, for the first time, a detailed comparison of the QFR enzymes from C. jejuni and H. pylori with that of W. succinogenes.
CpG methylation at the USF-binding site is important for the liver-specific transcription of the chipmunk HP-27 gene
Authors: Fujii Gen , Nakamura Yuki , Tsukamoto Daisuke , Ito Michihiko , Shiba Tadayoshi , Takamatsu Nobuhiko
Published: March 2006

The chipmunk hibernation-specific HP-27 gene is expressed specifically in the liver and has a CpG-poor promoter. To reveal how the liver-specific transcription of the HP-27 gene is regulated, we performed yeast one-hybrid screening of a chipmunk liver cDNA library. A 5′-flanking sequence of the HP-27 gene, extending from −170 to −140 and containing an E-box (5′-CACGTG-3′), is essential for the liver-specific transcription of HP-27. We used this sequence as bait and found that a ubiquitously expressed transcription factor, USF (upstream stimulatory factor), bound to the E-box. In COS-7 cells, USF activated transcription from the HP-27 gene promoter. We then used bisulphite genomic sequencing to analyse the methylation status of the four CpG dinucleotides that lie in the 5′-flanking sequence of the HP-27 gene up to −450, to investigate how the ubiquitously expressed USF activates transcription of the HP-27 gene only in the liver, while its transcription is repressed elsewhere. The only difference in methylation in the tissues tested was in the CpG dinucleotide in the USF-binding site, which was hypomethylated in the liver, but highly methylated in the kidney and heart. The specific methylation of the CpG dinucleotide at the USF-binding site impeded both the binding of USF and its transcriptional activation of the HP-27 gene. Chromatin immunoprecipitation using anti-USF antibodies revealed that USF bound to the HP-27 gene promoter in the liver, but not in the kidney or heart. Thus CpG methylation at the USF-binding site functions in establishing and maintaining tissue-specific transcription from the CpG-poor HP-27 gene promoter.
Viruses and the brain: from inflammation to dementia
Authors: Wang Tongguang , Rumbaugh Jeffrey A. , Nath Avindra
Published: March 2006

Many viruses cause encephalitis, but understanding the mechanisms by which viral infection leads to encephalopathy or dementia remain elusive. In many cases, inflammation generated by the host's attempt to combat the infection is itself implicated as a primary factor in causing neuronal dysfunction or degeneration. In this review, we outline the current state of knowledge regarding the pathophysiology of CNS (central nervous system) injury in viral infection. We focus our review on the neuropathogenesis of HIV type 1 (HIV-1)-associated dementia, because, within this class of infection, it is the best studied. We will also discuss the key similarities and differences in the pathological mechanisms of other important viral encephalitides. Understanding these mechanisms should ultimately enable development of immunomodulatory therapies for treating these infections, as well as other neuro-inflammatory conditions.
Bile acid profiles by capillary electrophoresis in intrahepatic cholestasis of pregnancy
Authors: Castaño Gustavo , Lucangioli Silvia , Sookoian Silvia , Mesquida Marcelo , Lemberg Abraham , Di Scala Mirta , Franchi Paula , Carducci Clyde , Tripodi Valeria
Published: March 2006

ICP (intrahepatic cholestasis of pregnancy) is characterized by pruritus and biochemical cholestasis, including raised SBAs (serum bile acids) and, usually, elevated aminotransferases levels. However, AHP (asymptomatic hypercholanaemia of pregnancy) is defined as the presence of total SBA levels above the cut-off value (11 μM) in healthy pregnant women, thus elevation of total SBAs do not necessarily reflect an ICP condition. The aim of the present study was to describe clinical, obstetric, perinatal and biochemical findings, as well as the SBA profile, in pregnant women studied in the third trimester of pregnancy in order to define characteristic patterns of individual bile acids that enable women with ICP to be distinguished from AHP and healthy pregnancies. Free and conjugated ursodeoxycholic (UDCA), cholic (CA), lithocholic (LCA), deoxycholic (DCA) and chenodeoxycholic (CDCA) acids were evaluated by CE (capillary electrophoresis) in 41 patients (15 of them simultaneously by HPLC), in 30 healthy pregnant women and in 10 non-pregnant women. A highly significant correlation between CE and HPLC for total SBAs (r=0.990) and for individual SBAs was found. Normal pregnant women had higher total SBA levels than non-pregnant women (due to an increase in taurine-conjugated dihydroxy SBAs). Women with ICP had higher levels of total SBAs, the free/conjugated ratio, LCA, CA, CDCA and DCA than normal pregnant women. Newborns from women with ICP had lower birth weight and gestational age. Women with AHP had higher levels of conjugated dihydroxy SBAs than normocholanaemic patients, without any evidence of a clinical difference. In conclusion, the present study has shown a clear difference in SBA profiles between ICP and normal pregnancies (including AHP), involving a shift towards a characteristic hydrophobic composition in women with ICP.
Determinants of short-term variation in arterial flow-mediated dilatation in healthy young men
Authors: Järvisalo Mikko J. , Jartti Laura , Marniemi Jukka , Rönnemaa Tapani , Viikari Jorma S. A. , Lehtimäki Terho , Raitakari Olli T.
Published: March 2006

Brachial artery FMD (flow-mediated dilatation) is widely used as a marker of systemic arterial endothelial function. FMD, however, shows considerable 25% day-to-day variation that hinders its clinical use. The reasons for this variability are poorly characterized. Therefore the present study was designed to clarify factors responsible for the hourly variation in endothelial function, including consuming a low-fat meal and circadian rhythms in endogenous hormonal levels. Brachial artery FMD, along with serum glucose, triacylglycerols (triglycerides) and levels of several hormones were measured six times per day on two separate days 1 week apart. On one day, the subjects (healthy males: n=12, mean age, 24 years) ate a light breakfast and a standardized lunch (23.5% fat, 48.7% carbohydrate and 27.8% protein). On the other day, they had a similar breakfast after which they fasted. Postprandial FMD values (both after breakfast and after lunch) were similar to baseline FMD. FMD showed a 28% hourly variation and 27% weekly variation. Variation in plasma levels of insulin (P=0.02) associated negatively and DHPG (3,4-dihydroxyphenylglycol) (P=0.001), a marker of sympathetic nervous activation, associated positively with variation in FMD. The effects of DHPG and insulin on FMD were independent of changes in baseline brachial artery diameter, although DHPG was also inversely associated with baseline diameter. Eating a regular low-fat meal does not have any measurable effects on brachial artery endothelial function. These data suggest that strict requirements for fasting conditions may be unnecessary when measuring peripheral endothelial function using the ultrasound technique. Circadian variation in serum insulin and sympathetic tone are physiological determinants of endothelial function.
Abnormal rhythmic oscillations of atrial natriuretic peptide and brain natriuretic peptide in chronic renal failure
Authors: Pedersen Erling B. , Bacevicius Egidijus , Bech Jesper N. , Solling Karsten , Pedersen Henrik B.
Published: March 2006

Secretion of ANP (atrial natriuretic peptide) and BNP (brain natriuretic peptide) is pulsatile in healthy humans. However, the patterns of secretion of ANP and BNP have not been studied in chronic renal failure. The aim of the present study was to test the hypotheses that ANP and BNP are secreted in pulses in dialysis patients, and that pulsatile secretion is regulated by prostaglandins. Blood samples were drawn every 2 min through an intravenously inserted plastic needle over a period of 1–2 h in 13 dialysis patients and 13 healthy control subjects (Study 1), and in 15 healthy control subjects, who participated in a randomized placebo-controlled cross-over study after treatment with indomethacin and placebo (Study 2). Plasma concentrations of ANP and BNP were determined by RIAs, and the results were analysed for pulsatile behaviour by Fourier transformation. The results from Study 1 showed that the secretion of ANP and BNP was pulsatile in nine patients with chronic renal failure. The maximum amplitude was significantly higher in chronic renal failure compared with control subjects for both ANP and BNP (ANP, 4.3 compared with 0.7 pmol/l; BNP, 2.0 compared with 0.3 pmol/l; values are medians) and correlated positively with the mean plasma level of ANP (ρ=0.900, P=0.001; n=9) and BNP (ρ=0.983, P=0.000; n=9). The frequency was the same for patients and controls. The results from Study 2 demonstrated pulsatile secretion in all subjects, but both the amplitude and frequency were unaffected by indomethacin. The maximum amplitude correlated positively with the mean plasma level of ANP and BNP during both placebo and indomethacin treatment. It can be concluded that the secretion of ANP and BNP is pulsatile with abnormally high amplitude in chronic renal failure, that prostaglandins apparently are not involved in the secretion of these peptides in healthy subjects and that the high secretion rate in chronic renal failure results in higher ANP and BNP in plasma.
First results with a modified multipole structure electron cyclotron resonance ion source
Authors: Suominen P. , Tarvainen O. , Koivisto H.
Published: March 2006

The radial magnetic-field strength is a critical parameter that affects the performance of an electron cyclotron resonance ion source (ECRIS). A method, known as the modified multipole structure (MMPS), for increasing the radial magnetic-field strengths has been developed and tested at the Department of Physics, University of Jyväskylä (JYFL). In this structure, the magnetic field is increased only at locations where the plasma flux hits the plasma chamber wall. The MMPS plasma chamber has been designed, constructed, and installed into the JYFL 6.4GHz ECRIS. Measurements have shown that the MMPS is especially effective for increasing the production of highly charged ions. Typically, the ion current increases by a factor of 2–3 in the case of highly charged ions such as Ar16+. The first results using the technique are presented in this article.
Ion current density profile control of a scalable linear ion source and its application
Authors: Scholze F. , Neumann H. , Tartz M. , Dienelt J. , Schlemm H.
Published: March 2006

We present a modular microwave excited electron cyclotron resonance type linear ion source concept that allows the adaptation of the ion beam dimensions to the requirements of the particular application. The ion beam current density profile is controlled by dividing the middle grid of a triple-grid system into segments of 2cm width. Each segment is separately switched between the negative accelerator grid voltage and a positive blocking voltage. By adjusting the pulse-to-pause ratio of each segment, the current density profile can be controlled from a homogeneous profile up to nearly arbitrary profiles. This ion source enables an in situ adaptation of ion beam profile. The application of a 2m linear ion source for hardening of stainless steel tools and the homogenization of the beam profile by segmented grids are demonstrated.
Modern options for hadron therapy of tumors
Authors: Becker Reinard
Published: March 2006

The use of accelerated ions for the removal of localized tumors without surgery has seen a wide development in the U.S., Japan, and Europe. Today new sites are under construction and some kind of competition has started to design and build the most versatile and/or the most cost effective facility. Developments like the laser ion source, which can create more than enough carbon ions in charge state 6, the electron beam ion source with ultrashort ion extraction and the rapid cycling medical synchrotron may contribute to reduce the investment cost as well as the cost per treatment.
Compact multibeamlet high-current injector for heavy-ion fusion drivers
Authors: Kwan J. W. , Bieniosek F. M. , Grote D. P. , Westenskow G. A.
Published: March 2006

Using curved electrodes in the injector, an array of converging beamlets can produce a beam with the envelope radius, convergence, and ellipticity matched to an electrostatic quadrupole channel. Experimental results were in good quantitative agreement with the simulation and have demonstrated the feasibility of this concept. Based on this approach, the size of a driver-scale injector system will be reduced, so the success of this experiment has significant economical and technical impacts on the architecture of heavy-ion fusion drivers.
Device for in situ cleaving of hard crystals
Authors: Schmid M. , Renner A. , Giessibl F. J.
Published: March 2006

Cleaving crystals in a vacuum chamber is a simple method for obtaining atomically flat and clean surfaces for materials with a preferential cleaving plane. Most in situ cleavers use parallel cutting edges that are applied from two sides on the sample. We found in ambient experiments that diagonal cutting pliers, where the cleavage force is introduced in a single point instead of a line, work very well also for hard materials. Here, we incorporate the diagonal cutting plier principle in a design compatible with ultrahigh-vacuum requirements. We show optical microscopy (millimeter scale) and atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with this device.
Spectral phase effects on nonlinear resonant photochemistry of 1,3-cyclohexadiene in solution
Authors: Carroll E. C. , Pearson B. J. , Florean A. C. , Bucksbaum P. H. , Sension Roseanne J.
Published: March 2006

We have investigated the ring opening of 1,3-cyclohexadiene to form 1,3,5-cis-hexatriene (Z-HT) using optical pulse shaping to enhance multiphoton excitation. A closed-loop learning algorithm was used to search for an optimal spectral phase function, with the effectiveness or fitness of each optical pulse assessed using the UV absorption spectrum. The learning algorithm was able to identify pulses that increased the formation of Z-HT by as much as a factor of 2 and to identify pulse shapes that decreased solvent fragmentation while leaving the formation of Z-HT essentially unaffected. The highest yields of Z-HT did not occur for the highest peak intensity laser pulses. Rather, negative quadratic phase was identified as an important control parameter in the formation of Z-HT.
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superconducting transition measurement by an electromagnetic acoustic transducer
Authors: Dutton B. , Gamboa-Perera F. , Acosta M. , Nahmad-Molinari Y.
Published: March 2006

An original noncontact measurement technique to determine the phase transition for the superconductor YBa2Cu3Ox is described. A piezoelectric is used to vibrate the sample normal to the superconductor surface, and a small coil which has a permanent magnet adhered to it, or an electromagnetic acoustic transducer (EMAT) for out-of-plane waves, is used to detect (by means of standard lock-in techniques) these vibrations, both on the Ohmic and the superconducting regimes as temperature is lowered. The magnitude of the induced voltage (by eddy currents) on the EMAT is plotted against temperature (T), and the changes in the conductivity in the Ohmic regime as well as during the superconducting transition (88.7<T<91.2K) are detected and compared to other more invasive methods. Furthermore, it is shown that the EMAT technique could allow us to explore the coupling between the net of vortex and the EMAT itself, well beyond the transition temperature, showing that the technique is promising to gather information on electron transport properties for fundamental studies or to provide reliable inspection into a production line.
Ultrasonic instrumentation for measurements in high magnetic fields. II. Pulsed magnetic fields
Authors: Suslov A. , Sarma Bimal K. , Ketterson J. B. , Balakirev F. , Migliori A. , Lacerda A.
Published: March 2006

We describe two state-of-the-art ultrasonic interferometers designed for pulse-echo ultrasound measurements in the short-pulse (40 ms) and intermediate-pulse (400 ms) 60 T magnets of the National High Magnetic Field Laboratory facilities at Los Alamos, NM. One interferometer utilizes a more commonly used scheme which has been adapted for a pulsed field environment. The second interferometer exploits digital processing of the undetected signal: the ultrasonic signal is digitized, stored in a computer, and later, analyzed.
Thermonuclear plasma with autocatalytic thermomagnetic current amplification by nuclear reactions from fusion neutrons
Authors: Winterberg F.
Published: March 2006

It is proposed to use the neutrons released from a deuterium-tritium or deuterium-deuterium fusion reaction to drive thermomagnetic currents in a plasma corona surrounding the fusion plasma through the heating of the corona with nuclear reactions by the neutrons released in the fusion reaction. Because the neutron reaction cross sections are larger for slow neutrons, it is proposed to slow them down in a moderator separated from the hot plasma of the corona, giving the configuration a striking similarity to a heterogeneous nuclear fission reactor. While in a fission reactor the separation makes possible a growing neutron chain reaction, it here makes possible the autocatalytic amplification of the thermomagnetic currents by an increase of the fusion reaction rate through a rise of the plasma pressure by the magnetic pressure of the thermomagnetic currents. This is expected to substantially increase the nτ product over its Lawson value.
Parametric estimation of thermoradiative properties of materials based on harmonic excitation
Authors: Agoudjil B. , Datcu S. , Boudenne A. , Ibos L. , Candau Y.
Published: March 2006

A simple device for the measurement of emissivity, thermal conductivity, and diffusivity of opaque materials is described. The measurement method is based on the use of a harmonic excitation of a material sample plate. The front surface of the sample is heated periodically and its temperature is measured using a thermocouple. The sample back surface temperature is obtained by infrared thermography. Half of the sample back surface is covered by a black paint of known emissivity used as a reference to compute the sample surface directional emissivity. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of experimental and theoretical heat transfer functions. Results are presented for a thermally thick sample of PVC, where the sample thickness is greater than the thermal diffusion length. The identified thermophysical properties are in agreement with literature values and reproducible results are obtained. Moreover, some limitations of the method are considered. First, the black paint layer influence on the heat transfer cannot be neglected in all the frequency ranges of measurement. Secondly, an accurate estimation of the thermal conductivity cannot be obtained without an exact knowledge of the heat transfer coefficient.
Molecular and electronic structure in NaCl electrolytes of varying concentration: Identification of spectral fingerprints
Authors: Aziz Emad F. , Zimina A. , Freiwald M. , Eisebitt S. , Eberhardt W.
Published: March 2006

Near edge x-ray absorption spectra at the Na K edge in aqueous NaCl electrolytes are presented as a function of concentration. The spectra are modeled by electronic structure calculations. We find and identify the orbital origin of two spectral fingerprints with sensitivity to the Na+–H2O distance and the Na+–Cl− distance in the electrolyte. Interionic interaction is found to be crucial for the description of the electrolytes at high concentrations.
Analysis of osmotic pressure data for aqueous protein solutions via a multicomponent model
Authors: Druchok M. , Kalyuzhnyi Yu. , Reščič J. , Vlachy V.
Published: March 2006

Integral equation theories and Monte Carlo simulations were used to study the Donnan equilibrium, which is established by an equilibrium distribution of a simple electrolyte between an aqueous protein-electrolyte mixture and an aqueous solution of the same simple electrolyte, when these two phases are separated by a semipermeable membrane. In order to describe the unusually low osmotic pressure found in many experiments we assumed that protein molecules can form dimers. The model solution contains proteins in a monomeric form, represented as charged hard spheres, or in a dimerized form, modeled as fused charged hard spheres. The counterions and coions were also modeled as charged hard spheres but of a much smaller size. The associative mean spherical and hypernetted-chain approximations were applied to this model. In addition, Monte Carlo computer simulations were performed for the same model system mimicking a lysozyme solution in the presence of 0.1M sodium chloride. Theory and simulations were found to be in reasonably good agreement for the thermodynamic properties such as chemical potential and osmotic pressure under these conditions. Using the theoretical approaches mentioned above, we analyzed the experimental data for the osmotic pressure of bovine serum albumin in 0.15M sodium chloride, human serum albumin solution (HSA) in 0.1M phosphate buffer, and lysozyme in sulphate and phosphate buffers. The theoretically determined osmotic coefficients were fitted to the existing experimental data in order to obtain the fraction of dimers in solution. Our analysis indicated that there was relatively small self-association of protein molecules for bovine serum albumin solutions at pH=5.4 and 7.3, with the fraction of dimers smaller than 10%, while at pH=4.5 the dimer fraction was equal to 50%. In the case of HSA solutions, strong negative deviations from the ideal value were found and at pH=8.0 a reasonably good agreement between the theory and experiment is obtained by assuming full dimerization. For HSA solution at pH=5.4, the best fit to the experimental results was obtained for a fraction of dimers equal to 80%.
Theory of dust self-organized convection in cylindrical discharges. I. The model and stationary nonlinear dust structures
Authors: Tsytovich V. N. , Vladimirov S. V. , Vaulina O. S. , Petrov O. F. , Fortov V. E.
Published: March 2006

The convection of dust particles in a plasma is related to the spatial gradients of dust charge distributions existing due to different plasma conditions in different parts of dusty structures. For many experiments, the convection appears as a result of convective perturbations of basic nonlinear self-organized states of the dust structures. Here, the set of nonlinear equations is derived suitable for the study of basic stationary dust structures as well as their convective perturbations. On its basis, the stationary nonlinear states of self-organized cylindrical dusty structures in a plasma are investigated. It is demonstrated that there is the broad range of plasma and dust parameters where the self-organized states exist. The characteristics of these basic structures are determined by a limited number of the controlling parameters such as the ion number density in the center of the structure and the plasma ionization level. The derived set of equations also forms the basis for further investigation of the dust convection.
Combination of perturbative and variational methods for calculating molecular spectra: Calculation of the υ=3–5 CH stretch overtone spectrum of CHF3
Authors: Sprague Megan M. , Ramesh Sai G. , Sibert Edwin L.
Published: March 2006

Highly excited states of the CHF3 molecule belonging to the third, fourth, and fifth Fermi polyad are calculated using a combination of the Van Vleck perturbation theory and a variational treatment. The perturbation theory preconditions the Hamiltonian matrix by transforming away all couplings except those between nearly degenerate states. This transformation is implemented so that eigenvalues can be found with significantly smaller matrices than that which would be needed in the original normal mode representation. Even with preconditioning, at the energies as high as 3–5 quanta in the CH stretch, it is not possible to directly diagonalize the Hamiltonian matrix due to the large basis sets required. Iterative methods, particularly the block-Davidson method, are explored for finding the eigenvalues. The methods are compared and the advantages discussed.
Time dependent density functional study of the photoionization dynamics of SF6
Authors: Stener M. , Toffoli D. , Fronzoni G. , Decleva P.
Published: March 2006

The B-spline linear combination of atomic orbitals method has been employed to study the valence and core photoionization dynamics of SF6. The cross section and asymmetry parameter profiles calculated at the time dependent density functional theory level have been found to be in fairly nice agreement with the experimental data, with the quality of the exchange-correlation statistical average of orbital potential results superior to the Van Leeuwen-Baerends 94 (LB94) ones [Phys. Rev. A 49, 2421 (1994)]. The role of response effects has been identified by a comparison of the time dependent density functional theory results with the Kohn-Sham ones interchannel coupling effects and autoionization resonances play an important role at low kinetic energies. Prominent shape resonances features have been analyzed in terms of “dipole prepared” continuum orbitals and interpreted as due to a large angular momentum centrifugal barrier as well as anisotropic (nonspherical) molecular effective potential. Finally, the method has been proven numerically stable, robust, and efficient, thanks to a noniterative implementation of the time dependent density functional theory equations and suitability of the multicentric B-spline basis set to describe continuum states from outer valence to deep core states.
Memory effects of carbon nanotubes as charge storage nodes for floating gate memory applications
Authors: Lu X. B. , Dai J. Y.
Published: March 2006

A nonvolatile flash memory device has been fabricated using carbon nanotubes (CNTs) as a floating gate embedded in HfAlO (the atomic ratio of Hf∕Al is 1:2) high-k tunneling/control oxides and its memory effect has been observed. Capacitance-voltage (C-V) measurements illustrated a 400mV memory window during the double C-V sweep from 3 to −3V performed at room temperature and 1MHz. Further studies on their programming characteristics revealed that electron is difficult to be written into the CNTs and the memory effect of the structures is mainly due to the holes traps. The memory window width can remain nearly unchanged even after 104s stressing, indicating excellent long term charge retention characteristics. We therefore suggest that the CNTs embedded in HfAlO can be potentially applied to floating gate flash memory devices.
Theoretical study of plasma effect on a conical shock wave
Authors: Kuo S. P. , Kuo Steven S.
Published: March 2006

Experiments conducted previously in a Mach 2.5 wind tunnel showed that localized plasma generated by an on-board 60Hz electric discharge in front of a 60° cone-shaped model considerably increases the shock angle of the attached shock generated by the cone model. Based on the measured power and cycle energy of the electric discharge, the estimated peak and average temperature enhancements were too low to justify the heating effect as a possible cause of the observed shock wave modification. In this work, a theory also using a cone model as the shock wave generator is presented to explain the observed plasma effect on the shock wave. Through electron-neutral elastic collisions and ion-neutral charge transfer collisions, plasma generated in front of the baseline shock front can deflect the incoming flow before it reaches the cone model; such a flow deflection modifies the structure of the shock wave generated by the cone model from a conic shape to a slightly curved one. The shock remains to be attached to the tip of the cone; however, the shock front moves upstream to increase the shock angle, consistent with the experimental results.
Cellulose derivatives as excellent dispersants for single-wall carbon nanotubes as demonstrated by absorption and photoluminescence spectroscopy
Authors: Minami Nobutsugu , Kim Yeji , Miyashita Kanae , Kazaoui Said , Nalini Balakrishnan
Published: March 2006

Sodium carboxymethylcellulose, an etherified derivative of cellulose, has been found to realize stable aqueous dispersion of single-wall carbon nanotubes (SWNTs) that is twenty times more concentrated than when a surfactant is used under the same condition. The dispersion as well as thin films prepared from it exhibits well-resolved near-infrared photoluminescence peaks originating from band-gap transitions in semiconducting SWNTs, a sign of isolated individual tubes. Mechanical stretching of the film strongly aligns the tubes, as demonstrated by considerable dichroism in their absorption spectra. Possessing high optical quality and uniformity, these densely dispersed SWNT films are expected to serve as an important platform for SWNTs’ optical, electrical, and optoelectronic applications, especially because cellulose derivatives are cheap, mass-produced, safe, water-processable, and environmentally benign.
Einstein relations for energy coupled particle systems
Authors: Kang Yeona , Jaen Enrique , Fortmann C. M.
Published: March 2006

Einstein relations define ratios for diffusion and drift currents for an ensemble of particles moving via probabilistic events such as hops. An Einstein relation was derived for charged particles constrained to move as an integral part of a system having an energy consideration routed in its material matrix. For example, the cases where a deformation of a matrix or lattice structure stores or releases free energy upon electron concentration change. Using an analysis based on energy gradients, diffusion, and the steady state, a thermodynamic framework for energy-coupled motion was developed and applied to protein folding. Findings include an infinite mobility condition arising from finite free energy gradients.
Compact resonant integrated microfluidic refractometer
Authors: Domachuk P. , Littler I. C. M. , Cronin-Golomb M. , Eggleton B. J.
Published: March 2006

We introduce a class of highly compact refractometers integrated onto a planar microfluidic geometry that demonstrates high resolution refractive index measurements in 50μm fluid channels utilizing a Fabry–Perot cavity formed between resonant Bragg grating reflectors. This cavity forms a resonant peak in the transmission spectrum which is dependent upon the refractive index of the fluid in the microfluidic channel. We demonstrate this class of refractometer using optical fiber Bragg gratings; to provide high resolution, intracavity losses are minimized using integrated collimating optics. The refractometer can resolve refractive index changes of 0.2% and is simulated using coupled mode theory.
Fabrication of enclosed nanochannels in poly(methylmethacrylate) using proton beam writing and thermal bonding
Authors: Shao P. E. , van Kan A. , Wang L. P. , Ansari K. , Bettiol A. A. , Watt F.
Published: March 2006

We report a technique for fabricating enclosed nanochannels in poly(methylmethacrylate) (PMMA) using proton beam writing coupled with thermal bonding. Using proton beam writing, straight-walled high-aspect-ratio channels can be directly fabricated through a relatively thick PMMA resist layer spin coated on a Kapton film. By thermally bonding the fabricated structures onto bulk PMMA, peeling off the Kapton substrate, and bonding the remaining exposed side to PMMA, enclosed high-aspect-ratio nano/microchannels can be fabricated. Such enclosed channels can be incorporated into fluidic polymeric devices, and the process is compatible with the fabrication of multilevel three-dimensional fluidic chips with vertical interconnects.
Wurtzite-type faceted single-crystalline GaN nanotubes
Authors: Liu Baodan , Bando Yoshio , Tang Chengchun , Shen Guozhen , Golberg Dmitri , Xu Fangfang
Published: March 2006

We report on the direct fabrication of single-crystalline wurtzite-type hexagonal GaN nanotubes via a newly designed, controllable, and reproducible chemical thermal-evaporation process. The nanotubes are single crystalline, have one end closed, an average outer diameter of ∼300nm, an inner diameter of ∼100nm, and a wall thickness of ∼100nm. The structure and morphology of the tubes are characterized using a scanning electron microscope and a transmission electron microscope. The cathodoluminescence of individual nanotubes is also investigated. The growth mechanism, formation kinetics, and crystallography of GaN nanotubes are finally discussed.
Kinetic-inductance-limited reset time of superconducting nanowire photon counters
Authors: Kerman Andrew J. , Dauler Eric A. , Keicher William E. , Yang Joel K. W. , Berggren Karl K. , Gol’tsman G. , Voronov B.
Published: March 2006

We investigate the recovery of superconducting NbN-nanowire photon counters after detection of an optical pulse at a wavelength of 1550nm, and present a model that quantitatively accounts for our observations. The reset time is found to be limited by the large kinetic inductance of these nanowires, which forces a tradeoff between counting rate and either detection efficiency or active area. Devices of usable size and high detection efficiency are found to have reset times orders of magnitude longer than their intrinsic photoresponse time.