bluuebunny/crossref_metadata_2025 huggingface dataset:
Gross primary production variability associated with meteorology, physiology, leaf area, and water supply in contrasting woodland and grassland semiarid riparian ecosystems
Authors: Jenerette G. D. , Scott R. L. , Barron‐Gafford G. A. , Huxman T. E.
Published: November 2009

Understanding ecosystem‐atmosphere carbon exchanges in dryland environments has been more challenging than in mesic environments, likely due to more pronounced nonlinear responses of ecosystem processes to environmental variation. To better understand diurnal to interannual variation in gross primary productivity (GPP) variability, we coupled continuous eddy‐covariance derived whole ecosystem gas exchange measurements with an ecophysiologic model based on fundamental principles of diffusion, mass balance, reaction kinetics, and biochemical regulation of photosynthesis. We evaluated the coupled data‐model system to describe and understand the dynamics of 3 years of growing season GPP from a riparian grassland and woodland in southern Arizona. The data‐model fusion procedure skillfully reproduced the majority of daily variation GPP throughout three growing seasons. While meteorology was similar between sites, the woodland site had consistently higher GPP rates and lower variability at daily and interannual timescales relative to the grassland site. We examined the causes of this variation using a new state factor model analysis that partitioned GPP variation into four factors: meteorology, physiology, leaf area, and water supply. The largest proportion of GPP variation was associated with physiological differences. The woodland showed a greater sensitivity than the grassland to water supply, while the grassland showed a greater sensitivity to leaf area. These differences are consistent with hypotheses of woody species using resistance mechanisms, stomatal regulation, and grassland species using resilience mechanisms, leaf area regulation, in avoiding water stress and have implications for future GPP sensitivity to climate variability following wood‐grass transitions.
Simultaneous determination of β-sitosterol, campesterol, stigmasterol, and brassicasterol in serum by high-performance liquid chromatography with electrochemical detection
Authors: Ito Nanako , Hakamata Hideki , Kusu Fumiyo
Published: November 2009

An HPLC-ECD method has been developed for the determination of phytosterols using the direct electrochemical oxidation of phytosterols.
Preparation, characterization and evaluation of a biopolymeric gold nanocomposite with antimicrobial activity
Authors: Chamundeeswari Munusamy , Sobhana S. S. Liji , Jacob Justin P. , Kumar M. Ganesh , Devi M. Pandima , Sastry Thotapalli P. , Mandal Asit B.
Published: November 2009

The present study describes the antimicrobial activity of C‐AuNp‐Amp (chitosan‐capped gold nanoparticles coupled with ampicillin). C‐AuNp‐Amp was synthesized using the wet precipitation method and characterized using FTIR (Fourier‐transform IR) spectroscopy and AFM (atomic force microscopy) techniques. The optimal level of ampicillin concentration that couples with the C‐AuNp nanocomposite was determined by using UV–visible spectroscopy. The agar‐well diffusion method was used to evaluate the antimicrobial activity, and the broth dilution assay was used to determine the MIC (minimum inhibitory concentration). The size of the ellipsoidal C‐AuNp‐Amp particles was found to be in the range of 50–100 nm. The FTIR spectrum confirms the bonding between amino groups of chitosan and carboxylic groups of ampicillin. The maximum coupling of ampicillin with C‐AuNp was found to be 4.07 mg/10 ml. These results revealed the antimicrobial efficacy of C‐AuNp‐Amp and a 2‐fold increase in activity was achieved when compared with that of free ampicillin. By reducing the antibiotic dosage to 50%, the side effects produced by antibiotics can be minimized.
Cystic fibrosis transmembrane regulator fragments with the Phe508 deletion exert a dual allosteric control over the master kinase CK2
Authors: Pagano Mario A. , Marin Oriano , Cozza Giorgio , Sarno Stefania , Meggio Flavio , Treharne Kate J. , Mehta Anil , Pinna Lorenzo A.
Published: November 2009

Cystic fibrosis mostly follows a single Phe508 deletion in CFTR (cystic fibrosis transmembrane regulator) (CFTRΔF508), thereby causing premature fragmentation of the nascent protein with concomitant alterations of diverse cellular functions. We show that CK2, the most pleiotropic protein kinase, undergoes allosteric control of its different cellular forms in the presence of short CFTR peptides encompassing the Phe508 deletion: these CFTRΔF508 peptides drastically inhibit the isolated catalytic subunit (α) of the kinase and yet up-regulate the holoenzyme, composed of two catalytic and two non-catalytic (β) subunits. Remarkable agreement between in silico docking and our biochemical data point to different sites for the CFTRΔF508 peptide binding on isolated CK2α and on CK2β assembled into the holoenzyme, suggesting that CK2 targeting may be perturbed in cells expressing CFTRΔF508; this could shed light on some pleiotropic aspects of cystic fibrosis disease.
MCP-1 causes cardiomyoblast death via autophagy resulting from ER stress caused by oxidative stress generated by inducing a novel zinc-finger protein, MCPIP
Authors: Younce Craig W. , Kolattukudy Pappachan E.
Published: November 2009

MCP-1 (monocyte chemotactic protein-1) plays a critical role in the development of heart failure that is known to involve apoptosis. How MCP-1 contributes to cell death involved in the development of heart disease is not understood. In the present study we show that MCP-1 causes death in cardiac myoblasts, H9c2 cells, by inducing oxidative stress which causes ER stress leading to autophagy via a novel zinc-finger protein, MCPIP (MCP-1-induced protein). MCPIP expression caused cell death, and knockdown of MCPIP attenuated MCP-1induced cell death. It caused induction of iNOS (inducible NO synthase), translocation of the NADPH oxidase subunit phox47 from the cytoplasm to the membrane, production of ROS (reactive oxygen species), and induction of ER (endoplasmic reticulum) stress markers HSP40 (heat-shock protein 40), PDI (protein disulfide-isomerase), GRP78 (guanine-nucleotide-releasing protein 78) and IRE1α (inositol-requiring enzyme 1α). It also caused autophagy, as indicated by beclin-1 induction, cleavage of LC3 (microtubule-associated protein 1 light chain 3) and autophagolysosome formation, and apoptosis, as indicated by caspase 3 activation and TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling) assay. Inhibitors of oxidative stress, including CeO2 nanoparticles, inhibited ROS formation, ER stress, autophagy and cell death. Specific inhibitors of ER stress inhibited autophagy and cell death as did knockdown of the ER stress signalling protein IRE1. Knockdown of beclin-1 and autophagy inhibitors prevented cell death. This cell death involved caspase 2 and caspase 12, as specific inhibitors of these caspases prevented MCPIP-induced cell death. Microarray analysis showed that MCPIP expression caused induction of a variety of genes known to be involved in cell death. MCPIP caused activation of JNK (c-Jun N-terminal kinase) and p38 and induction of p53 and PUMA (p53 up-regulated modulator of apoptosis). Taken together, these results suggest that MCPIP induces ROS/RNS (reactive nitrogen species) production that causes ER stress which leads to autophagy and apoptosis through caspase 2/12 and IRE1α–JNK/p38–p53–PUMA pathway. These results provide the first molecular insights into the mechanism by which elevated MCP-1 levels associated with chronic inflammation may contribute to the development of heart failure.
Paraoxonase 2 is down-regulated by the Pseudomonas aeruginosa quorumsensing signal N-(3-oxododecanoyl)-L-homoserine lactone and attenuates oxidative stress induced by pyocyanin
Authors: Horke Sven , Witte Ines , Altenhöfer Sebastian , Wilgenbus Petra , Goldeck Marion , Förstermann Ulrich , Xiao Junhui , Kramer Gerald L. , Haines Donovan C. , Chowdhary Puneet K. , Haley Robert W. , Teiber John F.
Published: November 2009

Two virulence factors produced by Pseudomonas aeruginosa are pyocyanin and N-(3-oxododecanoyl)-L-homoserine lactone (3OC12). Pyocyanin damages host cells by generating ROS (reactive oxygen species). 3OC12 is a quorum-sensing signalling molecule which regulates bacterial gene expression and modulates host immune responses. PON2 (paraoxonase-2) is an esterase that inactivates 3OC12 and potentially attenuates Ps. aeruginosa virulence. Because increased intracellular Ca2+ initiates the degradation of PON2 mRNA and protein and 3OC12 causes increases in cytosolic Ca2+, we hypothesized that 3OC12 would also down-regulate PON2. 3OC12 and the Ca2+ ionophore A23187 caused a rapid cytosolic Ca2+ influx and down-regulated PON2 mRNA, protein and hydrolytic activity in A549 and EA.hy 926 cells. The decrease in PON2 hydrolytic activity was much more extensive and rapid than decreases in protein, suggesting a rapid post-translational mechanism which blocks PON2's hydrolytic activity. The Ca2+ chelator BAPTA/AM [1,2-bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid tetrakis(acetoxymethyl ester)] diminished the ability of 3OC12 to decrease PON2, demonstrating that the effects are mediated by Ca2+. PON2 also has antioxidative properties and we show that it protects cells from pyocyanin-induced oxidative stress. Knockdown of PON2 by transfecting cells with siRNA (small interfering RNA) rendered them more sensitive to, whereas overexpression of PON2 protected cells from, pyocyanin-induced ROS formation. Additionally, 3OC12 potentiated pyocyanin-induced ROS formation, presumably by inactivating PON2. These findings support a key role for PON2 in the defence against Ps. aeruginosa virulence, but also reveal a mechanism by which the bacterium may subvert the protection afforded by PON2.
Insulin-stimulated phosphorylation of endothelial nitric oxide synthase at serine-615 contributes to nitric oxide synthesis
Authors: Ritchie Stuart A. , Kohlhaas Christine F. , Boyd Alasdair R. , Yalla Krishna C. , Walsh Kenneth , Connell John M. C. , Salt Ian P.
Published: November 2009

Insulin stimulates endothelial NO (nitric oxide) synthesis via PKB (protein kinase B)/Akt-mediated phosphorylation and activation of eNOS (endothelial NO synthase) at Ser-1177. In previous studies, we have demonstrated that stimulation of eNOS phosphorylation at Ser-1177 may be required, yet is not sufficient for insulin-stimulated NO synthesis. We therefore investigated the role of phosphorylation of eNOS at alternative sites to Ser-1177 as candidate parallel mechanisms contributing to insulin-stimulated NO synthesis. Stimulation of human aortic endothelial cells with insulin rapidly stimulated phosphorylation of both Ser-615 and Ser-1177 on eNOS, whereas phosphorylation of Ser-114, Thr-495 and Ser-633 was unaffected. Insulin-stimulated Ser-615 phosphorylation was abrogated by incubation with the PI3K (phosphoinositide 3-kinase) inhibitor wortmannin, infection with adenoviruses expressing a dominant-negative mutant PKB/Akt or pre-incubation with TNFα (tumour necrosis factor α), but was unaffected by high culture glucose concentrations. Mutation of Ser-615 to alanine reduced insulin-stimulated NO synthesis, whereas mutation of Ser-615 to aspartic acid increased NO production by NOS in which Ser-1177 had been mutated to an aspartic acid residue. We propose that the rapid PKB-mediated stimulation of phosphorylation of Ser-615 contributes to insulin-stimulated NO synthesis.
Regulation of plasma LDL: the apoB paradigm
Authors: Sniderman Allan D. , De Graaf Jacqueline , Couture Patrick , Williams Ken , Kiss Robert S. , Watts Gerald F.
Published: November 2009

The objectives of this analysis are to re-examine the foundational studies of the in vivo metabolism of plasma LDL (low-density lipoprotein) particles in humans and, based on them, to reconstruct our understanding of the governance of the concentration of plasma LDL and the maintenance of cholesterol homoeostasis in the hepatocyte. We believe that regulation of cholesterol homoeostasis within the hepatocyte is demonstrably more complex than envisioned by the LDL receptor paradigm, the conventional model to explain the regulation of plasma LDL and the fluxes of cholesterol into the liver, a model which was generated in the fibroblast but has never been fully validated in the hepatocyte. We suggest that the LDL receptor paradigm should be reconfigured as the apoB (apolipoprotein B) paradigm, which states that the rate at which LDL particles are produced is at least an important determinant of their concentration in plasma as the rate at which they are cleared from plasma and that secretion of cholesterol within VLDL (very-low-density lipoprotein) particles is an important mechanism of maintaining cholesterol homoeostasis within the hepatocyte. These two paradigms are not mutually exclusive. The LDL receptor paradigm, however, includes only one critical aspect of the regulation of plasma LDL, namely the rate at which LDL particles are cleared through the LDL receptor pathway, but ignores another – the rate at which LDL particles are added to the plasma compartment. The apoB paradigm includes both and points to a different model of how the hepatocyte achieves cholesterol homoeostasis in a complex metabolic environment.
Exercise and possible molecular mechanisms of protection from vascular disease and diabetes: the central role of ROS and nitric oxide
Authors: Newsholme Philip , Homem De Bittencourt Paulo I. , O' Hagan Ciara , De Vito Giuseppe , Murphy Colin , Krause Mauricio S.
Published: November 2009

It is now widely accepted that hypertension and endothelial dysfunction are associated with an insulin-resistant state and thus with the development of T2DM (Type 2 diabetes mellitus). Insulin signalling is impaired in target cells and tissues, indicating that common molecular signals are involved. The free radical NO• regulates cell metabolism, insulin signalling and secretion, vascular tone, neurotransmission and immune system function. NO• synthesis is essential for vasodilation, the maintenance of blood pressure and glucose uptake and, thus, if levels of NO• are decreased, insulin resistance and hypertension will result. Decreased blood levels of insulin, increased AngII (angiotensin II), hyperhomocysteinaemia, increased ADMA (asymmetric ω-NG,NG-dimethylarginine) and low plasma L-arginine are all conditions likely to decrease NO• production and which are associated with diabetes and cardiovascular disease. We suggest in the present article that the widely reported beneficial effects of exercise in the improvement of metabolic and cardiovascular health are mediated by enhancing the flux of muscle- and kidney-derived amino acids to pancreatic and vascular endothelial cells aiding the intracellular production of NO•, therefore resulting in normalization of insulin secretion, vascular tone and insulin sensitivity. Exercise may also have an impact on AngII and ADMA signalling and the production of pro- and anti-inflammatory cytokines in muscle, so reducing the progression and development of vascular disease and diabetes. NO• synthesis will be increased during exercise in the vascular endothelial cells so promoting blood flow. We suggest that exercise may promote improvements in health due to positive metabolic and cytokine-mediated effects.
Fourier transform microwave spectroscopy and molecular structure of the trans-1,2-difluoroethylene-hydrogen fluoride complex
Authors: Leung Helen O. , Marshall Mark D. , Amberger Brent K.
Published: November 2009

Guided by ab initio calculations, Fourier transform microwave rotation spectra in the 6.5–22 GHz region are obtained for the complex formed between trans-1,2-difluoroethylene and hydrogen fluoride, including the normal isotopomer and two singly substituted C13 species in natural abundance. Spectra are also obtained for the analogous three species formed using deuterium fluoride. Analysis of the spectra provides rotational and hyperfine constants that are used to determine a structure for trans-CHFCHF–HF. This structure is similar to that obtained for 1,1-difluoroethylene-HF [H. O. Leung et al., J. Chem. Phys. 131, 204301 (2009)] in that a primary, hydrogen bonding interaction exists between the HF donor and a F atom acceptor on the 1,2-difluoroethylene moiety, while a secondary interaction occurs between the F atom on the HF molecule and the H atom cis to the hydrogen-bonded F atom on the substituted ethylene and causes the hydrogen bond to deviate from linearity. Because the two F atoms and the two H atoms in trans-1,2-difluoroethylene form electrostatically equivalent pairs, the structure of the complex with HF provides insight into the contribution of steric effects to the observed geometries of fluoroethylene-protic acid complexes. A comparison of the observed hydrogen bond lengths and deviations from linearity in 1,1-difluoroethylene-HF and trans-1,2-difluoroethylene-HF suggests that the F atoms in trans-1,2-difluoroethylene are more nucleophilic than those in 1,1-difluoroethylene and that the H atoms are similarly more acidic. Ab initio calculations of electrostatic potentials mapped onto total electron density surfaces for these two molecules support these conclusions.
Fourier transform microwave spectroscopy and molecular structure of the 1,1-difluoroethylene-hydrogen fluoride complex
Authors: Leung Helen O. , Marshall Mark D. , Drake Tasha L. , Pudlik Tadeuz , Savji Nazir , McCune Daniel W.
Published: November 2009

Fourier transform microwave rotation spectra in the 7–21 GHz region are obtained for the complex formed between 1,1-difluoroethylene and hydrogen fluoride, including the normal isotopomer and two singly substituted C13 species obtained in natural abundance. Spectra are also obtained for the analogous three species formed using deuterium fluoride. Analysis of the spectra provides rotational and hyperfine constants that are used, in combination with information from the analogous complex, 1,1-difluoroethylene-acetylene, to determine a structure for CH2CF2–HF. This structure is similar to that obtained for vinyl fluoride-HF [G. C. Cole and A. C. Legon, Chem. Phys. Lett. 400, 419 (2004)] in that a primary, hydrogen bonding interaction exists between the HF donor and a F atom acceptor on the 1,1-difluoroethylene moiety, while a secondary interaction occurs between the F atom on the HF molecule and the H atom cis to the hydrogen-bonded F atom on the substituted ethylene and causes the hydrogen bond to deviate from linearity. A comparison of the structures of 1,1-difluoroethylene complexes with the protic acids HF, HCl, and HCCH demonstrates that the hydrogen bond length increases with decreasing gas-phase acid strength, whereas a comparison of HF complexes with vinyl fluoride, 1,1-difluoroethylene, and 1,1,2-trifluoroethylene indicates that the nucleophilicity of the F atoms decreases with increasing fluorine substitution, but that the secondary interaction length is remarkably similar in all three complexes.
Single-layered chrysotile nanotubes: A quantum mechanical ab initio simulation
Authors: D’Arco Philippe , Noel Yves , Demichelis Raffaella , Dovesi Roberto
Published: November 2009

Chrysotile single-layered nanotubes, obtained by wrapping the Mg3Si2O5(OH)4 lizardite monolayer along the (n,−n) hexagonal lattice vector, are simulated at the ab initio level by using an all electron 6-31G∗ basis set and the B3LYP functional for n varying from 14 to 24 (the nanotube radius R referred to the oxygen connecting the Mg and Si layers increases from 20 to 35 Å). Because of the full exploitation of the helical symmetry, recently implemented in the CRYSTAL code, the computational cost for the full self-consistent field (SCF) and gradient calculation increases only by a factor of 2 and 1.2, respectively, when passing from the lizardite monolayer [18 atoms and 236 AOs (atomic orbitals) in the unit cell] to the (24, −24) tube (864 atoms and 11 328 AOs). The total energy of the tubes is always larger than that of the lizardite monolayer; the difference ΔE decreases very rapidly with n; for the largest tube here considered (n=24) ΔE is as small as 2.7 kJ/mol per formula unit (f.u.); extrapolating to larger n values, at about R=50 Å, ΔE becomes smaller than 1 kJ mol f.u. Very large energy gains are observed for small n values during optimization after rolling, mainly due to the rotation of the SiO4 tetrahedra that are in the inner part of the cylinder (“normal rolling”); such a rigid rotation accounts for about 85% of the overall relaxation energy. “Inverse rolling” tubes (SiO4 on the external wall of the tube) are shown to be less stable than the corresponding “normal” tubes.
Monolayer graphene growth on sputtered thin film platinum
Authors: Kang Byung Jin , Mun Jeong Hun , Hwang Chan Yong , Cho Byung Jin
Published: November 2009

It is demonstrated that sputtered thin film platinum (Pt) can be used as a catalytic metal for graphene growth on metal. During the crystallization annealing, the sputtered Pt is crystallized mostly into Pt (111) orientation, maintaining excellent surface roughness with no sign of agglomeration. The relatively lower carbon solubility in Pt and the good surface roughness of the thin film Pt enable us to form a uniform monolayer graphene on Pt over the entire region of the thin film Pt/SiO2/Si substrate by carbon dissolution and segregation method processed in a methane ambient. The monolayer graphene grown on Pt has been successfully transferred to SiO2/Si substrate by simple wet etching of Pt. The results of Raman spectroscopic and scanning tunneling microscopic measurements of the synthesized graphene layer are presented.
Effects of surfactants and alignment on the physical properties of single-walled carbon nanotube buckypaper
Authors: Park Jin Gyu , Smithyman Jesse , Lin Chih-Yen , Cooke Adam , Kismarahardja Ade W. , Li Shu , Liang Richard , Brooks James S. , Zhang Chuck , Wang Ben
Published: November 2009

Single-walled carbon nanotubes were dispersed in an aqueous medium using surfactants and filtered to make entangled networks, called buckypaper (BP), and the Raman spectra of BP samples revealed the degree of entanglement and residual surfactant content. The temperature dependence of the G-band peak shift in the BP was found to depend on the reduction in residual surfactant and nanotube oxidation. The electrical conductivity was improved after removing the surfactant and increasing the nanotube alignment, although the temperature dependence of electrical resistivity still followed a variable range hopping conduction behavior. The mechanical properties were affected by the degree of entanglement, alignment, and residual surfactant content, and tensile properties were found to improve with the reduction in surfactant and enhancement of alignment.
Blue luminescence of SrTiO3 under intense optical excitation
Authors: Rubano A. , Paparo D. , Granozio F. Miletto , Scotti di Uccio U. , Marrucci L.
Published: November 2009

The blue-green photoluminescence emitted by pure and electron-doped strontium titanate under intense pulsed near-ultraviolet excitation is studied experimentally as a function of excitation intensity and temperature. Both emission spectra and time-resolved decays of the emission are measured and analyzed in the framework of simple phenomenological models. We find an interesting blue-to-green transition occurring for increasing temperatures in pure samples, which is absent in doped materials. The luminescence yield and decay rate measured as a function of temperature can be modeled well as standard activated behaviors. The leading electron-hole recombination process taking place in the initial decay is established to be second order, or bimolecular, in contrast to recent reports favoring a third-order interpretation as an Auger process. The temporal decay of the luminescence can be described well by a model based on two interacting populations of excitations, respectively identified with interacting defect-trapped (possibly forming excitons) and mobile charges. Finally, from the measured doping and sample dependence of the luminescence yield, we conclude that the radiative centers responsible for the luminescence are probably intrinsic structural defects other than bulk oxygen vacancies.
Luminescence emission from forward- and reverse-biased multicrystalline silicon solar cells
Authors: Bothe K. , Ramspeck K. , Hinken D. , Schinke C. , Schmidt J. , Herlufsen S. , Brendel R. , Bauer J. , Wagner J.-M. , Zakharov N. , Breitenstein O.
Published: November 2009

We study the emission of light from industrial multicrystalline silicon solar cells under forward and reverse biases. Camera-based luminescence imaging techniques and dark lock-in thermography are used to gain information about the spatial distribution and the energy dissipation at pre-breakdown sites frequently found in multicrystalline silicon solar cells. The pre-breakdown occurs at specific sites and is associated with an increase in temperature and the emission of visible light under reverse bias. Moreover, additional light emission is found in some regions in the subband-gap range between 1400 and 1700 nm under forward bias. Investigations of multicrystalline silicon solar cells with different interstitial oxygen concentrations and with an electron microscopic analysis suggest that the local light emission in these areas is directly related to clusters of oxygen.
Cosputtered Mn-doped Si thin films studied by x-ray spectroscopy
Authors: Ye Jian , Jiang Yong , Liu Qinghua , Yao Tao , Pan Zhiyun , Oyanagi H. , Sun Zhihu , Yan Wensheng , Wei Shiqiang
Published: November 2009

Substitutionally doped Si1−xMnx thin films were fabricated by a magnetron cosputtering method at a low growth temperature. X-ray absorption fine structure (XAFS) and x-ray diffraction (XRD) techniques were used to investigate the structures of the Si1−xMnx thin films. The XRD results exhibit that no secondary phases such as metallic Mn or Mn–Si compound can be detected. The detailed analysis of the extended XAFS together with the x-ray absorption near-edge structure spectra at the Mn K-edge unambiguously reveals that the doped Mn atoms are incorporated into the Si matrix and substitute for the Si sites in the Si lattice. The results clearly indicate that the Mn occupations in silicon thin films are quite sensitive to the growth conditions and the postannealing treatment.
Glutaraldehyde enhanced dielectrophoretic yeast cell separation
Authors: Gagnon Zachary , Mazur Jill , Chang Hsueh-Chia
Published: November 2009

We introduce a method for improved dielectrophoretic (DEP) discrimination and separation of viable and nonviable yeast cells. Due to the higher cell wall permeability of nonviable yeast cells compared with their viable counterpart, the cross-linking agent glutaraldehyde (GLT) is shown to selectively cross-link nonviable cells to a much greater extent than viable yeast. The DEP crossover frequency (cof) of both viable and nonviable yeast cells was measured over a large range of buffer conductivities (22 μS/cm–400 μS/cm) in order to study this effect. The results indicate that due to selective nonviable cell cross-linking, GLT modifies the DEP cof of nonviable cells, while viable cell cof remains relatively unaffected. To investigate this in more detail, a dual-shelled oblate spheroid model was evoked and fitted to the cof data to study cell electrical properties. GLT treatment is shown to minimize ion leakage out of the nonviable yeast cells by minimizing changes in cytoplasm conductivity over a large range of ionic concentrations. This effect is only observable in nonviable cells where GLT treatment serves to stabilize the cell cytoplasm conductivity over a large range of buffer conductivity and allow for much greater differences between viable and nonviable cell cofs. As such, by taking advantage of differences in cell wall permeability GLT magnifies the effect DEP has on the field induced separation of viable and nonviable yeasts.
Effects of viscoelasticity on the probability density functions in turbulent channel flow
Authors: Samanta Gaurab , Housiadas Kostas D. , Handler Robert A. , Beris Antony N.
Published: November 2009

The probability density functions (PDFs) of the velocity fluctuations and their derivatives of a viscoelastic turbulent channel flow are calculated and compared against those for a Newtonian fluid at a friction Reynolds number 180. The velocity fields in both cases are provided from previous and new direct numerical simulations. In the viscoelastic case, the Giesekus model is used at a friction Weissenberg number 50, a mobility parameter 1/900, and viscosity ratio 0.9, corresponding to 37.4% drag reduction. The skewness and the flatness factors, which are also calculated and presented as functions of the distance from the wall, further reveal and quantify the non-Gaussian characteristics of the turbulent structures and how they are distributed in the flow domain. With the presence of viscoelasticity the non-Gaussian character of the PDFs is typically further enhanced. In particular, larger asymmetries and much longer tails are typically observed in the viscoelastic PDFs. This indicates higher intermittency in the viscoelastic turbulent flow versus the Newtonian one, along with strong correlations between all scales of turbulence. Furthermore, we have also seen significant qualitative changes regarding the distribution of the non-Gaussian characteristics of the PDFs as a function of the distance from the wall. The most notable differences are seen in the PDFs of the shear and spanwise velocity components in the buffer and log-law regions, as well as in most of the components of the first and second order velocity derivatives. It is also found that in the log-law layer the PDFs of the logarithm of the dissipation and the pseudodissipation rate, as well as of the enstrophy, are almost Gaussian. In contrast, in the viscous sublayer and the buffer layer, significant deviations from the Gaussian shape are observed. Whereas the deviations from Gaussianity are more enhanced with viscoelasticity next to the wall, with the PDFs even more negatively skewed, away from the wall sometimes (i.e., for the logarithm of the enstrophy) they are decreased. All these findings are pointing out to a fairly complex picture for the interaction of viscoelasticity with turbulence that makes the task of developing turbulent viscoelastic models even more challenging.
Atomic motions in poly(vinyl methyl ether): A combined study by quasielastic neutron scattering and molecular dynamics simulations in the light of the mode coupling theory
Authors: Capponi S. , Arbe A. , Alvarez F. , Colmenero J. , Frick B. , Embs J. P.
Published: November 2009

Quasielastic neutron scattering experiments (time-of-flight, neutron spin echo, and backscattering) on protonated poly(vinyl methyl ether) (PVME) have revealed the hydrogen dynamics above the glass-transition temperature. Fully atomistic molecular dynamics simulations properly validated with the neutron scattering results have allowed further characterization of the atomic motions accessing the correlation functions directly in real space. Deviations from Gaussian behavior are found in the high-momentum transfer range, which are compatible with the predictions of mode coupling theory (MCT). We have applied the MCT phenomenological version to the self-correlation functions of PVME atoms calculated from our simulation data, obtaining consistent results. The unusually large value found for the λ-exponent parameter is close to that recently reported for polybutadiene and simple polymer models with intramolecular barriers.
Critical Casimir interaction of ellipsoidal colloids with a planar wall
Authors: Kondrat S. , Harnau L. , Dietrich S.
Published: November 2009

Based on renormalization group concepts and explicit mean field calculations, we study the universal contribution to the effective force and torque acting on an ellipsoidal colloidal particle, which is dissolved in a critical fluid and is close to a homogeneous planar substrate. At the same closest distance between the substrate and the surface of the particle, the ellipsoidal particle prefers an orientation parallel to the substrate, and the magnitude of the fluctuation-induced force is larger than if the orientation of the particle is perpendicular to the substrate. The sign of the critical torque acting on the ellipsoidal particle depends on the type of boundary conditions for the order parameter at the particle and substrate surfaces and on the pivot with respect to which the particle rotates.
On the role of surface plasmon polaritons in the formation of laser-induced periodic surface structures upon irradiation of silicon by femtosecond-laser pulses
Authors: Bonse Jörn , Rosenfeld Arkadi , Krüger Jörg
Published: November 2009

The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSSs) on single-crystalline silicon upon irradiation with single or multiple femtosecond-laser pulses (pulse duration τ=130 fs and central wavelength λ=800 nm) in air is studied experimentally and theoretically. In our theoretical approach, we model the LIPSS formation by combining the generally accepted first-principles theory of Sipe and co-workers with a Drude model in order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma. Our results are capable to explain quantitatively the spatial periods of the LIPSSs being somewhat smaller than the laser wavelength, their orientation perpendicular to the laser beam polarization, and their characteristic fluence dependence. Moreover, evidence is presented that surface plasmon polaritons play a dominant role during the initial stage of near-wavelength-sized periodic surface structures in femtosecond-laser irradiated silicon, and it is demonstrated that these LIPSSs can be formed in silicon upon irradiation by single femtosecond-laser pulses.
Reduced hole injection barrier for achieving ultralow voltage polymer space-charge-limited transistor with a high on/off current ratio
Authors: Chao Yu-Chiang , Lin Yi-Cheng , Dai Min-Zhi , Zan Hsiao-Wen , Meng Hsin-Fei
Published: November 2009

Vertical polymer space-charge limited transistor (SCLT) operated with an ultralow voltage is demonstrated. The influence of aging effect of the oxygen plasma treated indium tin oxide electrode on the hole injection barrier and on the transistor characteristics is investigated. By reducing the hole injection barrier, the on/off ratio as high as 104 is obtained at a collector to emitter voltage as low as −0.84 V. The low operation voltage is crucial to the development of low-power large-area polymer transistor array. Inverter characteristics are also demonstrated by connecting a SCLT with a load resistor.
Electron transport of folded graphene nanoribbons
Authors: Xie Yue E. , Chen Yuan Ping , Zhong JianXin
Published: November 2009

Recently, the AA-stack bilayer graphene nanoribbon (BGN) with a closed edge is observed in experiment. This new type of GN, we called folded GN (FGN), can be formed by folding a monolayer GN (MGN). Electron transport of the folded structures with different edges is studied. The FGNs show unique transport properties different from those of MGNs and BGNs. A metallic MGN with armchair edge (MAGN) is still metallic after folding. However, a semiconducting MAGN can be either semiconducting or metallic after folding, which depends on the width of MAGN and strength of interlayer coupling in the folded structure. The energy gap decreases with the increase of the coupling strength or width. As to the MGNs with zigzag edge (MZGNs), after folding they exhibit interesting conductance characteristics. The conductance steps around the Dirac point are even multiple of G0=2e2/h, while other conductance steps are odd multiple of G0. It indicates that the electron transport around the Dirac point in zigzag-edged FGNs (FZGNs) is similar to that in zigzag-edged BGNs (BZGNs), while electron transport far from the Dirac point is similar to that in zigzag-edged MGNs (MZGNs).
Improvement of the nonlinear dynamic response of a Z-tilts lead zirconate titanate-based compensation stage using the capacitor insertion method
Authors: Liu Chien-Hung , Chen Chieh-Li , Lee Hau-Wei , Jywe Wen-Yuh
Published: November 2009

This paper presents a Z-tilts compensation stage with three piezoelectric actuators and three guided hinges, which are a combination of a two-dimensional rotational hinge and a spring-type hinge. In order to reduce the nonlinearity of the three piezoelectric actuators, the capacitor insertion method was applied on each piezoelectric actuator. The relationship between the improved nonlinearity and the decreased displacement with various inserted capacitors is discussed and suitable capacitors for the stage are determined. A three-dimensional feedback measuring system composed of a laser interferometer and a quadrant photodiode detector was used to directly measure the real working position of the platform of the Z-tilts compensation stage without measuring the individual displacement of the three piezoelectric actuators. The minimum displacement and angular displacement of the Z-tilt stage were ±10 nm and ±0.1 arc sec, respectively. The error of the dynamic response of z, θx, and θy with amplitudes of 3 μm of a sine wave at 30 Hz were ±70 nm, ±0.1 arc sec, and ±0.4 arc sec, respectively, with the capacitor insertion method and a simple proportional-integral controller.
Extended model of the photoinitiation mechanisms in photopolymer materials
Authors: Liu Shui , Gleeson Michael R. , Sabol Dusan , Sheridan John T.
Published: November 2009

In order to further improve photopolymer materials for applications such as data storage, a deeper understanding of the photochemical mechanisms which are present during the formation of holographic gratings has become ever more crucial. This is especially true of the photoinitiation processes, since holographic data storage requires multiple sequential short exposures. Previously, models describing the temporal variation in the photosensitizer (dye) concentration as a function of exposure have been presented and applied to two different types of photosensitizer, i.e., Methylene Blue and Erythrosine B, in a polyvinyl alcohol/acrylamide based photopolymer. These models include the effects of photosensitizer recovery and bleaching under certain limiting conditions. In this paper, based on a detailed study of the photochemical reactions, the previous models are further developed to more physically represent these effects. This enables a more accurate description of the time varying dye absorption, recovery, and bleaching, and therefore of the generation of primary radicals in photopolymers containing such dyes.
H atom formation from benzene and toluene photoexcitation at 248 nm
Authors: Kovács Tamás , Blitz Mark A. , Seakins Paul W. , Pilling Michael J.
Published: November 2009

The technique of excimer laser excitation/Lyman alpha H atom laser induced fluorescence was used to investigate the formation of H atoms from the 248 nm photoexcitation of benzene and toluene. The H atom signal dependence on laser excitation energy demonstrated that it is produced from two photon photolysis of the aromatics; absorption of the first photon populates the bound B12u level followed by absorption from this level to a dissociative level, which produces H atoms, among other potential channels. Analysis of the data yields the second photon absorption cross section to produce H and is equal to 1.0 and 5.2×10−19 cm2 for benzene and toluene, respectively. In addition, the yield of H atoms was observed to be pressure dependent. This is because at sufficiently high pressures the nanosecond lifetime of the B12u state can be pressure quenched and hence may compete with the absorption of the second photon. The yields of H atoms were determined as a function of pressure for a range of the laser energies and with various collider gases. The analysis of these data allowed the total absorption cross section for the second photon to be determined and is equal to 2.8 and 1.7×10−17 cm2 for benzene and toluene, respectively. In addition, the rate constants for quenching B12u with various gases (He, Ar, N2, and O2) were determined. This large absorption coefficient for the second photon implies that with a pulsed laser source of 248 nm it is difficult to avoid aromatic photodissociation. We highlight a few previous studies that may need to be reevaluated in the light of the results from this study.
Photochemistry of 3-hydroxyflavone inside superfluid helium nanodroplets
Authors: Lehnig R. , Pentlehner D. , Vdovin A. , Dick B. , Slenczka A.
Published: November 2009

3-hydroxyflavone is a prototype system for excited state intramolecular proton transfer which is one step of a closed loop photocycle. It was intensively studied for the bare molecule and for the influence of solvents. In the present paper this photocycle is investigated for 3-hydroxyflavone and some hydrated complexes when doped into superfluid helium droplets by the combined measurement of fluorescence excitation spectra and dispersed emission spectra. Significant discrepancies in the proton transfer behavior to gas phase experiments provide evidence for the presence of different complex configurations of the hydrated complexes in helium droplets. Moreover, for bare 3-hydroxyflavone and its hydrated complexes the proton transfer appears to be promoted by the helium environment.
High electron mobility and low sheet resistance in lattice-matched AlInN/AlN/GaN/AlN/GaN double-channel heterostructure
Authors: Zhang S. , Li M. C. , Feng Z. H. , Liu B. , Yin J. Y. , Zhao L. C.
Published: November 2009

High electron mobility and low sheet resistance were achieved in lattice-matched AlInN/AlN/GaN/AlN/GaN double-channel (DC) heterostructure. Two-dimensional electron gas (2DEG) of the DC heterostructure was divided into the double channels and the room-temperature mobility was increased to 1430 cm2/V s by reducing the 2DEG density in each channel, compared with low electron mobility (1090 cm2/V s) for lattice-matched AlInN/AlN/GaN single-channel heterostructure. It was found that the 2DEG mobility was limited by thickness of the AlN interlayer between the double channels. After the structure optimization, the room temperature electron mobility of the DC heterostructure reached 1570 cm2/V s with sheet resistance of 222 Ω/◻.
Spectrally resolved confocal microscopy for laser mode imaging and beam characteristic investigations
Authors: Brezna W. , Smoliner J.
Published: November 2009

In this letter, confocal optical microscopy is used to investigate the intensity patterns of an infrared vertical cavity surface emitting laser in three dimensions with high spectral resolution. The measurements were performed between the near field (Fresnel) regime and the far field (Fraunhofer) regime. The calculated intensity patterns were found to be in good agreement with the measured intensity distribution. The calculations together with the measurements can be used to determine the phase relation between different positions inside the gain medium.
Ultrafast carrier mobilities in high-resistivity iron-doped Ga0.69In0.31As photoconducting antennas
Authors: Sengupta Suranjana , Wilke Ingrid , Dutta Partha. S.
Published: November 2009

We report measurements of terahertz (THz) frequency radiation pulses emitted by photoconducting (PC) antennas fabricated from high-resistivity Fe-doped Ga0.69In0.31As. The Ga0.69In0.31As:Fe was grown using a hybrid vertical Bridgman and gradient freezing directional solidification process. GaxIn1−xAs crystals were uniformly doped with Fe atoms to obtain high-resistivity (∼107 Ω cm). The ultrafast carrier mobility in this material is about three orders of magnitude higher than in GaxIn1−xAs thin films grown by molecular beam epitaxy. The bandgap of Ga0.69In0.31As:Fe is low enough (∼1 eV) to use compact Yb-based multiwatt lasers operating at 1.1 μm for photoexcitation of Ga0.69In0.31As based PC antennas for high power THz emission.
Hybrid InP-based photonic crystal lasers on silicon on insulator wires
Authors: Halioua Y. , Karle T. J. , Raineri F. , Monnier P. , Sagnes I. , Roelkens G. , Van Thourhout D. , Raj R.
Published: November 2009

We report on InP-based photonic crystal lasers operating at 1.585 μm at room temperature, integrated with and evanescently coupled to silicon on insulator (SOI) waveguides. By optically pumping at 1.18 μm through the SOI wires, pulsed laser emission from line defect photonic crystal waveguides accurately aligned (<30 nm) to the silicon circuitry is demonstrated.
Excited and ionized states of the ozone molecule with full triples coupled cluster methods
Authors: Musiał Monika , Kucharski Stanisław A. , Zerzucha Piotr , Kuś Tomasz , Bartlett Rodney J.
Published: November 2009

The role of connected triple excitations in coupled cluster (CC) calculations of vertical excitation energies, ionization potentials, and the electron affinity of the ozone molecule is evaluated. The equation of motion (EOM) and Fock space (FS) multireference CC approaches with full triples have been used in the calculations. The effect of the T3 and R3 operators significantly improve the EOM CCSD results for all considered quantities. A similar behavior is observed in the case of the FS-CC calculations. The FS-CC calculations with full triples have been obtained only for the intermediate Hamiltonian realization of the FS approach as the standard formulation diverges. The latter results are rigorously linked, and less expensive since smaller matrices are diagonalized.
On nonadiabatic coupling vectors in time-dependent density functional theory
Authors: Tavernelli Ivano , Curchod Basile F. E. , Rothlisberger Ursula
Published: November 2009

In this note, we show that the development for the calculation of nonadiabatic coupling vectors in the framework of TDDFT introduced by the authors in the series of recent publications [E. Tapavicza et al., Phys. Rev. Lett.98, 023001 (2007); I. Tavernelli et al., J. Chem. Phys.130, 124107 (2009)] is rigorous and fully equivalent to the one proposed by Sugino and co-workers [C. P. Hu et al., J. Chem. Phys.127, 064103 (2007)]. Specific applications of our formulation are also discussed.
Control of free space propagation of Airy beams generated by quadratic nonlinear photonic crystals
Authors: Dolev Ido , Ellenbogen Tal , Voloch-Bloch Noa , Arie Ady
Published: November 2009

We present experimentally the control of free space propagation of an Airy beam. This beam is generated by a nonlinear wave mixing process in an asymmetrically poled nonlinear photonic crystal. Changing the quasi-phase matching conditions, e.g., the crystal temperature or pump wavelength, alters the location of the Airy beam peak intensity along the same curved trajectory. We explain that the variation in the beam shape is caused by noncollinear interactions. Owing to the highly asymmetric shape of nonlinear crystal in the Fourier space, these noncollinear interactions are still relatively efficient for positive (nonzero) phase mismatch.
Molecular cooperativity in the dynamics of glass-forming systems: A new insight
Authors: Hong L. , Gujrati P. D. , Novikov V. N. , Sokolov A. P.
Published: November 2009

The mechanism behind the steep slowing down of molecular motions upon approaching the glass transition remains a great puzzle. Most of the theories relate this mechanism to the cooperativity in molecular motion. In this work, we estimate the length scale of molecular cooperativity ξ for many glass-forming systems from the collective vibrations (the so-called boson peak). The obtained values agree well with the dynamic heterogeneity length scale estimated using four-dimensional NMR. We demonstrate that ξ directly correlates to the dependence of the structural relaxation on volume. This dependence presents only one part of the mechanism of slowing down the structural relaxation. Our analysis reveals that another part, the purely thermal variation in the structural relaxation (at constant volume), does not have a direct correlation with molecular cooperativity. These results call for a conceptually new approach to the analysis of the mechanism of the glass transition and to the role of molecular cooperativity.