bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of augmented vasoconstriction induced by 5‐hydroxytryptamine in aortic rings from spontaneously hypertensive rats
Authors: Budzyn K , Ravi R M , Miller A A , Sobey C G
Published: June 2008

Background and purpose:

To test whether development of enhanced vasoconstriction to 5‐hydroxytryptamine (5‐HT; serotonin) in SHR was temporally related to hypertension, elevated vascular superoxide (O2−) levels, decreased NO bioavailability, or increased contractile effects of cyclooxygenase or rho‐kinase and/or PKC.

Experimental approach:

We examined systolic blood pressure (SBP), vascular O2−, and 5‐HT‐induced contractile responses of aortic segments from 4‐ and 8‐week‐old WKY and SHR.

Key results:

SBP was 35% higher in SHR than WKY at 4 weeks and 60% higher at 8 weeks. Contractile responses to 5‐HT were similar in WKY and SHR at 4 weeks, but were markedly augmented in SHR at 8 weeks. The NO synthase inhibitor, L‐NAME, enhanced contractile responses to 5‐HT markedly in both strains at 4 weeks and in WKY at 8 weeks, but only very modestly in SHR at 8 weeks. These functional differences were associated with higher O2− levels in SHR versus WKY at 8 weeks, but not at 4 weeks. The rho‐kinase inhibitor, Y‐27632, and the PKC inhibitor, Ro 31‐8220, each only modestly attenuated contractions in WKY and SHR in each age group, and their effects in each strain were more pronounced at 8 weeks. The cyclooxygenase inhibitor, indomethacin, had no effect on contractile responses.

Conclusions and implications:

Development of augmented vascular contractile responses to 5‐HT in SHR is preceded by hypertension. It is associated with increased vascular O2− levels and reduced modulatory effects of NO, and is unlikely to be due to enhanced activity of rho‐kinase, PKC or cyclooxygenase.

British Journal of Pharmacology (2008) 155, 210–216; doi:10.1038/bjp.2008.247; published online 16 June 2008
Zebrafish: an emerging technology for in vivo pharmacological assessment to identify potential safety liabilities in early drug discovery
Authors: Barros T P , Alderton W K , Reynolds H M , Roach A G , Berghmans S
Published: June 2008

The zebrafish is a well‐established model organism used in developmental biology. In the last decade, this technology has been extended to the generation of high‐value knowledge on safety risks of novel drugs. Indeed, the larval zebrafish appear to combine advantages of whole organism phenotypic assays and those (rapid production of results with minimal resource engagement) of in vitro high‐throughput screening techniques. Thus, if appropriately evaluated, it can offer undeniable advantages in drug discovery for identification of target and off‐target effects. Here, we review some applications of zebrafish to identify potential safety liabilities, particularly before lead/candidate selection. For instance, zebrafish cardiovascular system can be used to reveal decreases in heart rate and atrial–ventricular dissociation, which may signal human ether‐a‐go‐go‐related gene (hERG) channel blockade. Another main area of interest is the CNS, where zebrafish behavioural assays have been and are further being developed into screening platforms for assessment of locomotor activity, convulsant and proconvulsant liability, cognitive impairment, drug dependence potential and impaired visual and auditory functions. Zebrafish also offer interesting possibilities for evaluating effects on bone density and gastrointestinal function. Furthermore, available knowledge of the renal system in larval zebrafish can allow identification of potential safety issues of drug candidates on this often neglected area in early development platforms. Although additional validation is certainly needed, the zebrafish is emerging as a versatile in vivo animal model to identify off‐target effects that need investigation and further clarification early in the drug discovery process to reduce the current, high degree of attrition in development.

British Journal of Pharmacology (2008) 154, 1400–1413; doi:10.1038/bjp.2008.249; published online 16 June 2008
The Importance of Patents for Scientists
Authors: Scott Sue
Published: June 2008

Patents have become a hot topic and the subject of much media attention. If your main source of information about patents is the newspapers, you could be forgiven for having an extremely distorted view of what patents are, what they do, and what benefits and problems are associated with them. All scientists want to be able to improve the world in some way, whether by contributing in a fundamental way to the fund of human knowledge or by delivering new and valuable technology. If you are a scientist making inventions, it is increasingly important that you should have an understanding of the importance of patents in the modern world, and should have sufficient understanding of the patent system to make sure that your aims for your inventions are achievable. This talk sets out some basic facts about patents and also de-bunks some the most common misapprehensions about patents.
Biotransformation of p‐methoxyphenylacetonitrile into p‐methoxyphenylacetic acid by resting cells of Bacillus subtilis
Authors: Chen Jing , Zheng Yu‐Guo , Shen Yin‐Chu
Published: June 2008

Resting cells of Bacillus subtilis ZJB‐063 were used for the direct transformation of MOPAN (p‐methoxyphenylacetonitrile) to MOPAA (p‐methoxyphenylacetic acid), which is an important pharmaceutical intermediate. The B. subtilis ZJB‐063 culture conditions for the production of nitrilase and the reaction conditions for this nitrilase‐mediated conversion were optimized. The maximum production of nitrilase was achieved when glucose and a combination of ammonium sulfate and yeast powder were added as carbon and nitrogen sources respectively. Previously reported inducers were found to be unnecessary for the production of nitrilase from B. subtilis ZJB‐063, which indicated that this nitrilase appeared to be constitutive. However, when ε‐caprolactam (6‐hexanolactam) was added as the inducer, B. subtilis ZJB‐063 exhibited nitrile hydratase and amidase activity. The maximum conversion of MOPAN into MOPAA (specific activity 17.03 units·g−1DCW; DCW is dry cell weight) was observed in a solution containing 50 mM phosphate buffer (pH 7.0), 10 mM MOPAN, 2.7 mg DCW·ml−1 wet resting cells and 5% (v/v) DMSO for 4 h at 32 °C. MOPAN (10 mM) was completely converted into MOPAA (9.65 mM) in 5 h in shake flasks without the formation of p‐methoxyphenylacetamide. The small deviation of MOPAA (9.65 mM) from the theoretical amount (10 mM) may be due to partial consumption of the products by B. subtilis ZJB‐063. Both MOPAN and MOPAA inhibited the hydrolysis at concentrations above 15 mM. Scale up of the reaction to 200 ml in a bubble bioreactor shortened the reaction time compared with the reactions performed in shake flasks.
Bioengineering functional human aortic vascular smooth‐muscle strips in vitro
Authors: Hecker Louise , Khait Luda , Welsh Michael J. , Birla Ravi
Published: June 2008

The contraction and relaxation of VSM (vascular smooth muscle) are responsible for the maintenance of vascular tone, which is a major determinant of blood pressure. However, the molecular events leading to the contraction and relaxation of VSM are poorly understood. The development of three‐dimensional bioengineered tissues provides an opportunity to investigate the molecular events controlling vascular tone in vitro. In the present study we used fibrin‐gel casting to bioengineer functional VSM strips from primary human aortic VSM cells. Our bioengineered VSM strips are functionally similar to VSM in vivo and remained viable in culture for up to 5 weeks. VSM strips demonstrate spontaneous basal tone and can generate an active force (contraction) of up to 85.2 μN on stimulation with phenylephrine. Bioengineered VSM strips exhibited Ca2+‐dependent contraction and calcium‐independent relaxation. The development of functional bioengineered VSM tissue provides a new in vitro model system that can be used to investigate the molecular events controlling vascular tone.
Proteomics of Grade 3 infiltrating ductal carcinoma in Malaysian Chinese breast cancer patients
Authors: Othman M. Izani , Majid M. I. A. , Singh Manjit , Subathra S. , Seng Liang , Gam Lay‐Harn
Published: June 2008

Breast cancer is the leading cause of cancer‐related mortality and morbidity among women worldwide and IDC (infiltrating ductal carcinoma) is the most common type of invasive breast cancer. The changes in the biological behaviour of cancer tissue can be predicted by measuring the differential protein expression of normal and cancerous tissues. Using a combination of SDS/PAGE and LC (liquid chromatography)–MS/MS (tandem MS), we identified 82 common and differentially expressed proteins from normal and cancerous breast tissues in 20 Malaysian Chinese patients with IDC. These proteins are extracted from the normal and cancerous tissue of patients and therefore represent the actual proteins involved in cancer development. Proteins identified possibly have significant roles in the development of breast cancer in Malaysian Chinese patients in view of their consistent expression in most of the patients, although some of the proteins had not been detected in earlier studies that were mostly carried out in Western countries. This observation suggests that molecular mechanisms leading to breast cancer development in this region may not be identical with those leading to IDC in Western regions.
Development of transgenic Artemisia annua (Chinese wormwood) plants with an enhanced content of artemisinin, an effective anti‐malarial drug, by hairpin‐RNA‐mediated gene silencing
Authors: Zhang Ling , Jing Fuyuan , Li Fupeng , Li Meiya , Wang Yuliang , Wang Guofeng , Sun Xiaofen , Tang Kexuan
Published: June 2008

Artemisinin is an effective anti‐malarial drug isolated from Artemisia annua L. (Chinese wormwood), but the content of artemisinin in A. annua is low. In the present study we explored the possibility of using genetic engineering to increase the artemisinin content of A. annua by suppressing the expression of SQS (squalene synthase), a key enzyme of sterol pathway (a pathway competitive with that of artemisinin biosynthesis) by means of a hairpin‐RNA‐mediated RNAi (RNA interference) technique. A total of 23 independent transgenic A. annua plants were obtained through Agrobacterium tumefaciens‐mediated transformation, which was confirmed by PCR and Southern‐blot analyses. HPLC‐evaporative light‐scattering detection analysis showed that the artemisinin content of some transgenic plants was significantly increased, with the highest values reaching 31.4 mg/g dry weight, which is about 3.14‐fold the content observed in untransformed control plants. Real‐time reverse transcription–PCR analysis demonstrated that the expression of SQS was suppressed significantly, and GC–MS analysis showed that sterol was efficiently decreased in the transgenic plants. The present study demonstrated that genetic‐engineering strategy of RNAi is an effective means of increasing artemisinin content in plants.
Knockdown of Pdcd4 results in induction of proprotein convertase 1/3 and potent secretion of chromogranin A and secretogranin II in a neuroendocrine cell line
Authors: Lankat‐Buttgereit Brigitte , Müller Sabine , Schmidt Harald , Parhofer Klaus G. , Gress Thomas M. , Göke Rüdiger
Published: June 2008

Background information. Pdcd4 (programmed cell death 4) is up‐regulated during apoptosis and seems to play an important role as a tumour suppressor. To gain further insights into its biological functions, we suppressed Pdcd4 expression in the neuroendocrine cell line Bon‐1 via siRNA (small interfering RNA) technology.

Results. Using this cell line, we found that suppression of Pdcd4 resulted in an increased release of CgA (chromogranin A) and Sg II (secretogranin II), and was accompanied by an up‐regulation of intracellular PC1 (proprotein convertase 1/3). The enhanced secretion of CgA and Sg II seemed to be mediated by an activation of protein kinase Akt via PI3K (phosphoinositide 3‐kinase). In accordance with this, inhibition of PI3K activity and, thereby, reduced phosphorylation of Akt was shown to enhance Pdcd4 expression. Neither the PKC (protein kinase C) signal transduction cascade nor the MAPK (mitogen‐activated protein kinase) pathway seemed to play a role in the regulation of CgA and Sg II secretion by Pdcd4.

Conclusions. CgA is considered to be a marker for neuroendocrine tumours, and up‐regulation of PC1 has been reported in various types of cancers. The repression of PC1 by Pdcd4 may represent a novel mechanism for the function of Pdcd4 as a tumour suppressor. Our results are of particular interest, as we observed that pioglitazone, an oral medication used in the treatment of Type 2 diabetes, decreased Pdcd4 levels, activated Akt, increased CgA and Sg II secretion and augmented PC1 protein in Bon‐1 cells. Enhanced PC1 levels, leading to improved processing of proinsulin and proglucagon, may contribute to the benefits of pioglitazone therapy. The in vivo relevance of our findings was highlighted by data indicating elevated CgA amounts in the sera of patients treated with pioglitazone. This is the first study connecting Pdcd4 levels, secretion behaviour of neuroendocrine cells and regulation of PI3K activity.
How do surfactants and DTT affect the size, dynamics, activity and growth of soluble lysozyme aggregates?
Authors: Kumar Satish , Ravi Vijay Kumar , Swaminathan Rajaram
Published: June 2008

The early intermediates in the protein aggregation pathway, the elusive soluble aggregates, play a pivotal role in growth and maturation of ordered aggregates such as amyloid fibrils. Blocking the growth of soluble oligomers is an effective strategy to inhibit aggregation. To decipher the molecular mechanisms and develop better strategies to arrest aggregation, it is imperative to understand how the size, molecular dynamics, activity and growth kinetics of soluble aggregates are affected when aggregation is inhibited. With this objective, in the present study we have investigated the influence of additives such as SDS, CTAB (cetyltrimethylammonium bromide) and DTT (dithiothreitol) on the slow aggregation of HEWL (hen eggwhite lysozyme) at pH 12.2. For this purpose, techniques such as steady-state and time-resolved fluorescence anisotropy of covalently labelled dansyl probe, gel-filtration chromatography, estimation of free thiol groups, thioflavin T and ANS (8-anilinonaphthalene-1-sulfonic acid) fluorescence, CD and atomic-force microscopy were employed to monitor the soluble oligomers over a period spanning 30 days. The results of the present study reveal that: (i) the spontaneous formation of soluble aggregates is irreversible and abolishes activity; (ii) the initial growth of aggregates (0–24 h) is promoted by a gradual increase in the exposure of hydrophobic surfaces; (iii) subsequently intermolecular disulfide bonds are critical for the assembly and stability of aggregates; (iv) the tight molecular packing inside large aggregates which contributed to slow (∼5 ns) and restricted segmental motion of dansyl probe was clearly loosened up in the presence of additives, enabling fast (1–2 ns) and free motion (unlike DTT, the size of lysozyme complexes with surfactants, was large, due to a conglomeration of proteins and surfactants); (v) the aggregates show reduced helical content compared with native lysozyme, except in the presence of SDS; and (vi) DTT was more potent than SDS/CTAB in arresting the growth of aggregates.
PRH/Hex: an oligomeric transcription factor and multifunctional regulator of cell fate
Authors: Soufi Abdenour , Jayaraman Padma-Sheela
Published: June 2008

The PRH (proline-rich homeodomain) [also known as Hex (haematopoietically expressed homeobox)] protein is a critical regulator of vertebrate development. PRH is able to regulate cell proliferation and differentiation and is required for the formation of the vertebrate body axis, the haematopoietic and vascular systems and the formation of many vital organs. PRH is a DNA-binding protein that can repress and activate the transcription of its target genes using multiple mechanisms. In addition, PRH can regulate the nuclear transport of specific mRNAs making PRH a member of a select group of proteins that control gene expression at the transcriptional and translational levels. Recent biophysical analysis of the PRH protein has shown that it forms homo-oligomeric complexes in vivo and in vitro and that the proline-rich region of PRH forms a novel dimerization interface. Here we will review the current literature on PRH and discuss the complex web of interactions centred on this multifunctional protein.
Lipidomic analysis of Toxoplasma gondii tachyzoites rhoptries: further insights into the role of cholesterol
Authors: Besteiro Sébastien , Bertrand-Michel Justine , Lebrun Maryse , Vial Henri , Dubremetz Jean-François
Published: June 2008

Rhoptries are secretory organelles involved in the virulence of the human pathogen Toxoplasma gondii. In the present study we have used HPLC and capillary GLC to isolate and quantify lipids from whole Toxoplasma cells and their purified rhoptries. This comparative lipidomic analysis revealed an enrichment of cholesterol, sphingomyelin and, most of all, saturated fatty acids in the rhoptries. These lipids are known, when present in membranes, to contribute to their rigidity and, interestingly, fluorescence anisotropy measurements confirmed that rhoptry-derived membranes have a lower fluidity than membranes from whole T. gondii cells. Moreover, although rhoptries were initially thought to be highly enriched in cholesterol, we demonstrated that cholesterol is present in lower proportions, and we have provided additional evidence towards a lack of involvement of rhoptry cholesterol in the process of host-cell invasion by the parasite. Indeed, depleting the cholesterol content of the parasites did not prevent the secretion of protein-containing rhoptry-derived vesicles and the parasites could still establish a structure called the moving junction, which is necessary for invasion. Instead, the crucial role of host cholesterol for invasion, which has already been demonstrated [Coppens and Joiner (2003) Mol. Biol. Cell 14, 3804–3820], might be explained by the need of a cholesterol-rich region of the host cell we could visualize at the point of contact with the attached parasite, in conditions where parasite motility was blocked.
Prohormone convertases 1/3 and 2 together orchestrate the site-specific cleavages of progastrin to release gastrin-34 and gastrin-17
Authors: Rehfeld Jens F. , Zhu Xiaorong , Norrbom Christina , Bundgaard Jens R. , Johnsen Anders H. , Nielsen John E. , Vikesaa Jonas , Stein Jeffrey , Dey Arunangsu , Steiner Donald F. , Friis-Hansen Lennart
Published: June 2008

Cellular synthesis of peptide hormones requires PCs (prohormone convertases) for the endoproteolysis of prohormones. Antral G-cells synthesize the most gastrin and express PC1/3, 2 and 5/6 in the rat and human. But the cleavage sites in progastrin for each PC have not been determined. Therefore, in the present study, we measured the concentrations of progastrin, processing intermediates and α-amidated gastrins in antral extracts from PC1/3-null mice and compared the results with those in mice lacking PC2 and wild-type controls. The expression of PCs was examined by immunocytochemistry and in situ hybridization of mouse G-cells. Finally, the in vitro effect of recombinant PC5/6 on progastrin and progastrin fragments containing the relevant dibasic cleavage sites was also examined. The results showed that mouse G-cells express PC1/3, 2 and 5/6. The concentration of progastrin in PC1/3-null mice was elevated 3-fold. Chromatography showed that cleavage of the Arg36Arg37 and Arg73Arg74 sites were grossly decreased. Accordingly, the concentrations of progastrin products were markedly reduced, α-amidated gastrins (-34 and -17) being 25% of normal. Lack of PC1/3 was without effect on the third dibasic site (Lys53Lys54), which is the only processing site for PC2. Recombinant PC5/6 did not cleave any of the dibasic processing sites in progastrin and fragments containing the relevant dibasic processing sites. The complementary cleavages of PC1/3 and 2, however, suffice to explain most of the normal endoproteolysis of progastrin. Moreover, the results show that PCs react differently to the same dibasic sequences, suggesting that additional structural factors modulate the substrate specificity.
Plasma cell adaptation to enhance particle acceleration
Authors: Ragheb M. S.
Published: June 2008

A plasma study is performed in order to construct a cell for plasma acceleration purpose. As well, a multicell design is introduced for the injection of beam driver application. The suggested idea is experimentally demonstrated for two plasma cell configuration. The preformed plasma is obtained by a symmetrically driven capacitive audio frequency discharge. It is featured by its moderate pressure of 0.1–0.2Torr, low consumption power of 130W maximum, low discharge voltage and frequency up to 950V and 20kHz, respectively, and high plasma density from 1011to1015cm−3. The electron temperature obtained by Langmuir double probe varies from 1 up to 16eV. It is observed that the increases of the discharge voltage and frequency enlarge the plasma parameters to their maximum values. The plasma cell filled with different gases demonstrates that the Ar and He gases manifest the highest ionization efficiency exceeding 100% at 950V and 20kHz. The formed plasma is cold; its density is uniform and stable along the positive column for long competitive lifetime. Showing that it follows the conditions to enhance particle acceleration and in conjunction with its periphery devices form a plasma cell that could be extended to serve this purpose. Demonstrating that an injected electron beam into the extended preformed plasma could follow, to long distance, a continuous trajectory of uniform density. Such plasma generated by H2 or Ar gases is suggested to be used, respectively, for low-density or higher density beam driver.
Acidification of three-dimensional emeraldine polymers: Search for minimum energy paths from base to salt
Authors: Cavazzoni Carlo , Colle Renato , Farchioni Riccardo , Grosso Giuseppe
Published: June 2008

We present a numerical simulation of the HCl acidification process of a three-dimensional semiconducting emeraldine base (EB) polymer leading to the corresponding metallic emeraldine salt form. We have searched minimum energy paths connecting the initial configuration, composed of two EB polymer chains per cell each one attached by two HCl molecules, with the Pc2a polaronic configuration which is the final state of the acidification process. For this aim, the variational nudged elastic band method has been adopted. We provide a pictorial representation of the acidification process at T=0K, monitoring the EB protonation and the evolution of the polymeric chains and of the positions of the Cl− counterions on the lowest potential energy surface. To include also temperature effects, we have explored the potential energy surface around the final equilibrium configuration, heating the system and following its dynamics by the Car–Parrinello procedure.
System for measuring the coordinates of tire surfaces in transient conditions when rolling over obstacles: Description of the system and performance analysis
Authors: Castellini Paolo , Di Giuseppe Andrea
Published: June 2008

This paper describes the development of a system for measuring surface coordinates (commonly known as “shape measurements”) which is able to give the temporal evolution of the position of the tire sidewall in transient conditions (such as during braking, when there are potholes or when the road surface is uneven) which may or may not be reproducible. The system is based on the well-known technique of projecting and observing structured light using a digital camera with an optical axis which is slanted with respect to the axis of the projector. The transient nature of the phenomenon has led to the development of specific innovative solutions as regards image processing algorithms. This paper briefly describes the components which make up the measuring system and presents the results of the measurements carried out on the drum bench. It then analyses the performance of the measuring system and the sources of uncertainty which led to the development of the system for a specific dynamic application: impact with an obstacle (cleat test). The measuring system guaranteed a measurement uncertainty of 0.28mm along the Z axis (the axial direction of the tire) with a measurement range of 250(X)×80(Y)×25(Z)mm3, with the tire rolling at a speed of up to 30km∕h.
Universal properties of a single polymer chain in slit: Scaling versus molecular dynamics simulations
Authors: Dimitrov D. I. , Milchev A. , Binder Kurt , Klushin Leonid I. , Skvortsov Alexander M.
Published: June 2008

We revisit the classical problem of a polymer confined in a slit in both of its static and dynamic aspects. We confirm a number of well known scaling predictions and analyze their range of validity by means of comprehensive molecular dynamics simulations using a coarse-grained bead-spring model of a flexible polymer chain. The normal and parallel components of the average end-to-end distance, mean radius of gyration and their distributions, the density profile, the force exerted on the slit walls, and the local bond orientation characteristics are obtained in slits of width D=4÷10 (in units of the bead diameter) and for chain lengths N=50÷300. We demonstrate that a wide range of static chain properties in normal direction can be described quantitatively by analytic model—independent expressions in perfect agreement with computer experiment. In particular, the observed profile of confinement-induced bond orientation is shown to closely match theory predictions. The anisotropy of confinement is found to be manifested most dramatically in the dynamic behavior of the polymer chain. We examine the relation between characteristic times for translational diffusion and lateral relaxation. It is demonstrated that the scaling predictions for lateral and normal relaxation times are in good agreement with our observations. A novel feature is the observed coupling of normal and lateral modes with two vastly different relaxation times. We show that the impact of grafting on lateral relaxation is equivalent to doubling the chain length.
Dynamic heterodyne near field scattering
Authors: Magatti D. , Alaimo M. D. , Potenza M. A. C. , Ferri F.
Published: June 2008

The technique heterodyne near field scattering (HNFS), originally developed for low-angle static light scattering, has also been implemented for carrying out dynamic light scattering. While the classical dynamic light scattering method measures the intensity-intensity correlation function, dynamic HNFS gives directly the field-field correlation function, without any assumption on the statistical properties of the sample, as the ones required by the Siegert relation. The technique has been tested with calibrated Brownian particles and its performances compared to those of the classical dynamic light scattering method.
Cluster conformations and multipole distributions in ionic fluids. I. Two-dimensional systems of mobile ions
Authors: Mehrabi Ali Reza , Sahimi Muhammad
Published: June 2008

A new association-biased Monte Carlo (MC) method is proposed for efficient simulation of association and dissociation of ions in an ionic fluid. The method is then utilized to carry out extensive MC simulations, in order to study the properties of ionic fluids in two-dimensional systems that consist of mobile ions. The size distributions of the ionic clusters, their conformations, as well as the clusters’ multipole distributions are computed over wide ranges of temperature T and ions’ density ρ. At any given T, bonded dipolar pairs are dominant in the insulating phase, but larger clusters with an even number of ions are also present. In the conducting phase at the same T, however, single (free) ions are abundant, while clusters of larger sizes are also present. As for the conformations of the clusters, at any T, perturbed folded structures are dominant in the insulating phase, whereas perturbed linear chains are the dominant conformation in the conducting phase at the same T. Moreover, ionic clusters with closed loops are rarely formed, if at all, over the range of T that we study. As T decreases, more clusters with symmetrical conformations are formed. The multipole distributions are shown to be accurate indicators for the various types of conformations of the ionic clusters. They are also shown to be accurate means of differentiating the conformations of ionic clusters that may appear to be only slightly different, and may be difficult to distinguish otherwise, as the multipoles are sensitive to the details of the conformations. Some exact results are presented for the dipoles and quadrupoles of several types of cluster conformations. These results give rise, for the first time, to a numerical “spectroscopy” of ionic fluids, whereby each conformation is associated with distinct values of the dipole and quadrupole of the ionic cluster. We also suggest a new method of locating the critical locus Tc(ρ) that separates the conducting and insulating phases—the Kosterlitz–Thouless transition—based only on the size distribution of the ionic clusters and its dependence on the ions’ density.
Relaxation transition due to different cooling processes in a superconducting levitation system
Authors: Zhou You-He , Zhang Xing-Yi , Zhou Jun
Published: June 2008

We present an experimental study of relaxation of vertical and horizontal force components in a high-temperature superconducting levitation system, with different initial cooling process after fixing the levitated body in an expected position statically. In the experiment, the bulk YBaCuO cylinder superconductor and the permanent magnet disk are employed. For a selected levitation height (LH) and a lateral displacement (LD) of the system, the experimental results show that the relaxations of the vertical and horizontal forces are strongly dependent on the initial cooling height (CH). With CH decreasing, the transition of the lateral force from repulsion to attraction is found as well as the changing characteristics with time from decrease to increase. Additionally, when LH is fixed at the CH, the transition phenomenon is also observed in the levitation force behavior and their relaxation under different LDs.
Noncontact to contact tunneling microscopy in self-assembled monolayers of alkylthiols on gold
Authors: Park Jeong Young , Qi Yabing , Ratera Imma , Salmeron M.
Published: June 2008

The mechanical interaction between a scanning tunneling microscopy (STM) probe and hexadecane (C16) alkylthiol molecules in a self-assembled monolayer was investigated by sensing the force during constant current mode STM imaging. The force regime changed from attractive to repulsive over the insulating molecule islands under feedback control of the current. The repulsive force on the molecule was strongly dependent on the setpoint value of the current during STM operation. In our experiments, the threshold for contact was found at a tunneling current of 1pA when the sample bias is 2V. At higher current, the apparent height of molecular islands changed logarithmically with current. In addition, the current as a function of applied load revealed a stepwise increase, indicative of discrete molecular tilting events. A tunneling decay constant β of =0.53±0.02Å−1 was obtained based on the measurement of the height of molecules and the tunneling current.
Many body effects on the phase separation and structure of dense polymer-particle melts
Authors: Hall Lisa M. , Schweizer Kenneth S.
Published: June 2008

Liquid state theory is employed to study phase transitions and structure of dense mixtures of hard nanoparticles and flexible chains (polymer nanocomposites). Calculations are performed for the first time over the entire compositional range from the polymer melt to the hard sphere fluid. The focus is on polymers that adsorb on nanoparticles. Many body correlation effects are fully accounted for in the determination of the spinodal phase separation instabilities. The nanoparticle volume fraction at demixing is determined as a function of interfacial cohesion strength (or inverse temperature) for several interaction ranges and nanoparticle sizes. Both upper and lower critical temperature demixing transitions are predicted, separated by a miscibility window. The phase diagrams are highly asymmetric, with the entropic depletion-like lower critical temperature occurring at a nanoparticle volume fraction of ∼10%, and a bridging-induced upper critical temperature at ∼95% filler loading. The phase boundaries are sensitive to both the spatial range of interfacial cohesion and nanoparticle size. Nonmonotonic variations of the bridging (polymer-particle complex formation) demixing boundary on attraction range are predicted. Moreover, phase separation due to many body bridging effects occurs for systems that are fully stable at a second order virial level. Real and Fourier space pair correlations are examined over the entire volume fraction regime with an emphasis on identifying strong correlation effects. Special attention is paid to the structure near phase separation and the minimum in the potential of mean force as the demixing boundaries are approached. The possibility that nonequilibrium kinetic gelation or nanoparticle cluster formation preempts equilibrium phase separation is discussed.
Spin-glass behavior in ferromagnetic Fe[Fe(CN)6]⋅xH2O nanoparticles
Authors: Mukadam M. D. , Kumar Amit , Yusuf S. M. , Yakhmi J. V. , Tewari R. , Dey G. K.
Published: June 2008

The magnetic properties of the nanoparticles of hexacyanometallate based molecular magnetic compound Fe[Fe(CN)6]⋅xH2O have been investigated using dc magnetization and the frequency dependent real part of ac susceptibility χac′ techniques. The magnetic properties of these nanoparticles with an average particle diameter ∼50 nm have been compared with that of the bulk polycrystalline sample. A reduction in the Curie temperature as well as low coercivity and remanent magnetization have been found for the nanoparticles compared to those for the bulk polycrystalline sample. The maximum magnetization for the nanoparticles is also found to be smaller as compared to that for the bulk polycrystalline sample. For the nanoparticles, the peak temperature Tp in the χac′ vs T curve has been found to shift to a higher temperature with increasing frequency and this frequency dependence is described well by a power law. The fitting yields the relaxation time constant τ0=1.3×10−13 s, the freezing temperature Tg=10.63 K, and the critical exponent zν=5.5±0.3. For the bulk polycrystalline sample, no such shift in the ac susceptibility peak temperature has been observed. The time dependence of the thermoremanent magnetization has been observed only for the nanoparticles, which could be represented well with a stretched exponential law. The observed magnetic behavior of the nanocrystalline sample indicates the presence of disordered spins (leading to a spin-glass behavior) in these ferromagnetically ordered particles.
Pump-wavelength dependence of terahertz radiation via optical rectification in (110)-oriented ZnTe crystal
Authors: Li Dong , Ma Guohong
Published: June 2008

The optical pump-wavelength-dependent generation and detection of terahertz wave in (110)-oriented ZnTe crystal were demonstrated. By using femtosecond laser pulses, terahertz radiation was generated. Both simulations and experimental results show that the terahertz wave in the frequency range of about 4–1 THz can be obtained by tuning the pumping wavelength from 700 to 900 nm. The theoretical analysis shows that the matching between the optical group velocity and terahertz phase velocity plays an important role for terahertz frequency tuning. The present studies also demonstrate that both the terahertz generation and detection are applicable in a single nonlinear optical crystal.
The electrostrictive effect in ferroelectric 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 thick films
Authors: Uršič Hana , Škarabot Miha , Hrovat Marko , Holc Janez , Skalar Miha , Bobnar Vid , Kosec Marija , Muševič Igor
Published: June 2008

The electromechanical behavior of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN-0.35PT) thick films, screen printed and fired on alumina substrates, was investigated using an atomic force microscope. A quadratic relation between the induced strain and the electric field was found and is discussed here. The electrostrictive coefficient M33 was determined to be 7.6×10−16 m2/V2. The determined tetragonal crystal structure, the frequency independence of the dielectric maxima as a function of temperature, and the hysteresis loop with a remanent polarization of 31 μC/cm2 and a coercive field of 40 kV/cm confirm the ferroelectric nature of the developed 0.65PMN-0.35PT thick films.
A multicentric approach to the calculation of nondipolar effects in molecular photoemission
Authors: Toffoli Daniele , Decleva Piero
Published: June 2008

The linear combination of atomic orbital approach to the calculation of the molecular continuum spectrum with B-spline basis functions has been extended to calculate first-order nondipolar corrections to the photoelectron angular distributions. The authors give an account of the new implementation and provide an application to the calculation of dipolar and nondipolar contributions to the photoelectron angular distributions from the SF6 molecule. The proposed approach is a promising tool for the investigation of such effects in the photoemission of large molecules and clusters.
Simulating asymmetric colloidal mixture with adhesive hard sphere model
Authors: Jamnik A.
Published: June 2008

Monte Carlo simulation and Percus–Yevick (PY) theory are used to investigate the structural properties of a two-component system of the Baxter adhesive fluids with the size asymmetry of the particles of both components mimicking an asymmetric binary colloidal mixture. The radial distribution functions for all possible species pairs, g11(r), g22(r), and g12(r), exhibit discontinuities at the interparticle distances corresponding to certain combinations of n and m values (n and m being integers) in the sum nσ1+mσ2 (σ1 and σ2 being the hard-core diameters of individual components) as a consequence of the impulse character of 1-1, 2-2, and 1-2 attractive interactions. In contrast to the PY theory, which predicts the delta function peaks in the shape of gij(r) only at the distances which are the multiple of the molecular sizes corresponding to different linear structures of successively connected particles, the simulation results reveal additional peaks at intermediate distances originating from the formation of rigid clusters of various geometries.
Terahertz spectroscopy of carbon nanotubes embedded in a deformable rubber
Authors: Rungsawang R. , Geethamma V. G. , Parrott E. P. J. , Ritchie D. A. , Terentjev E. M.
Published: June 2008

The dielectric response and anisotropic properties of natural rubber with embedded multiwall carbon nanotubes (CNTs) are studied in the 0.2–3THz frequency range using terahertz transmission spectroscopy. Natural rubber acts as an invisible and insulating medium in this frequency range, allowing examination of isolated CNTs. The complex dielectric function is obtained with different CNT loadings by using a superposition formula. In highly loaded composites, we find a significant increase in the imaginary part of the dielectric function, related to a change in conductivity due to percolation. The deformable rubber matrix allows the alignment of CNTs by stretching. We investigated the response of aligned nanotubes to polarized terahertz radiation and it shows the evidence of primary electron transport along the tube axis.
Surface stress effects on the resonant properties of silicon nanowires
Authors: Park Harold S.
Published: June 2008

The purpose of the present work is to quantify the coupled effects of surface stresses and boundary conditions on the resonant properties of silicon nanowires. We accomplish this by using the surface Cauchy–Born model, which is a nonlinear, finite deformation continuum mechanics model that enables the determination of the nanowire resonant frequencies including surface stress effects through solution of a standard finite element eigenvalue problem. By calculating the resonant frequencies of both fixed/fixed and fixed/free ⟨100⟩ silicon nanowires with unreconstructed {100} surfaces using two formulations, one that accounts for surface stresses and one that does not, it is quantified how surface stresses cause variations in nanowire resonant frequencies from those expected from continuum beam theory. We find that surface stresses significantly reduce the resonant frequencies of fixed/fixed nanowires as compared to continuum beam theory predictions, while small increases in resonant frequency with respect to continuum beam theory are found for fixed/free nanowires. It is also found that the nanowire aspect ratio, and not the surface area to volume ratio, is the key parameter that correlates deviations in nanowire resonant frequencies due to surface stresses from continuum beam theory.
Coherent A1g and Eg phonons of antimony
Authors: Ishioka Kunie , Kitajima Masahiro , Misochko Oleg V.
Published: June 2008

We report the ultrafast dynamics of the coherent A1g and Eg phonons of antimony as a function of temperature and optical polarization. Like in bismuth, the two phonon modes exhibit nearly π/2 difference in their initial phase, suggesting their different coupling strengths with photoexcited electrons. The dependence of the phonon amplitude on the optical polarization and temperature indicates the generation of the coherent A1g phonons through both displacive and Raman processes, rather than a purely displacive one. In contrast, the generation of the coherent Eg phonons can be understood within Raman framework alone.
Influence of A-site codoping on ferroelectricity of quantum paraelectric SrTiO3
Authors: Wei T. , Zhu C. , Wang K. F. , Cai H. L. , Zhu J. S. , Liu J.-M.
Published: June 2008

The low temperature dielectric and ferroelectric properties of SrTiO3, with constant averaged A-site ionic size but different A-site disorder degrees induced by A-site cation size mismatching through the codoping of Ca and Ba, are investigated. Upon the increasing A-site disorder degree, the dielectric property shows different behaviors from individually Ca- or Ba-doped SrTiO3 where the averaged A-site ionic size varies linearly with the doping. The transition from the quantum paraelectric state to relaxorlike ferroelectric state and eventually to normal ferroelectric state upon the increasing A-site disorder degree is revealed. The physics underlying these phenomena is discussed based on the A-site size mismatch effect.
High frequency electromagnetic interference shielding behaviors of Ti3SiC2∕Al2O3 composites
Authors: Shi Suilin , Zhang Lingzhen , Li Junshou
Published: June 2008

Ti 3 Si C 2 ∕ Al 2 O 3 composites were prepared by hot-pressing sintering process. The dielectric permittivity and electromagnetic interference (EMI) shielding effectiveness (SE) is measured for the composites at the frequency range of 12.4–18GHz (Ku band). The experimental results show that the composites exhibit high complex permittivities at Ku-band frequencies, depending on the Ti3SiC2 content; both the real and imaginary permittivities of the composites increase with the increasing Ti3SiC2 content. The EMI SE of the composite was greatly enhanced with the addition of the Ti3SiC2 filler and increase with the dc conductivity of the composites. The high value of EMI SE shows the potential of the Ti3SiC2∕Al2O3 composite as EMI shielding materials.
The self-sustained current oscillation and the dynamics in superlattices under the action of electric and magnetic fields
Authors: Yang Gui , Meng Hao , Zhang Ling-Feng , Zhou Shi-Ping
Published: June 2008

Self-sustained time-dependent current oscillations have been found in weakly coupled GaAs∕AlAs superlattices when the sequential resonant tunneling between adjacent quantum wells is the main electron transport mechanism. The oscillation regime was tunable by varying the doping densities and applied dc voltages. Based on the discrete sequential tunneling model, we theoretically studied the magnetic field dependence of the oscillation. The magnetic field B seems to be favorable for the formation of the static electric-field domains and to depress the current oscillation. Thus, the oscillation regime will be narrowed as the magnetic field strength increases. Driven by a transverse external microwave excitation, the system shows interesting nonlinear behaviors like quasiperiodicity, frequency locking, and periodicity.
Tuning field-induced energy gap of bilayer graphene via interlayer spacing
Authors: Guo Yufeng , Guo Wanlin , Chen Changfeng
Published: June 2008

Our first-principles calculations reveal surprisingly high sensitivity of the field-induced energy gap of bilayer graphene to changes in its interlayer spacing. Small adjustments in the interlayer spacing near its equilibrium value produce large modulations in the gap over a wide range of field strength. We elucidate the mechanism for the extremely effective gap tuning by examining the interlayer charge redistribution driven by the coupled electric field and nanomechanical effect.
Photocurrent of CdSe nanocrystals on single-walled carbon nanotube-field effect transistor
Authors: Jeong Seung Yol , Lim Seong Chu , Bae Dong Jae , Lee Young Hee , Shin Hyun Jin , Yoon Seon-Mi , Choi Jae Young , Cha Ok Hwan , Jeong Mun Seok , Perello David , Yun Minhee
Published: June 2008

CdSe nanocrystals (NCs) have been decorated on single-walled carbon nanotubes (SWCNTs) by combining a method of chemically modified substrate along with gate-bias control. CdSe∕ZnS core/shell quantum dots were negatively charged by adding mercaptoacetic acid. The silicon oxide substrate was decorated by octadecyltrichlorosilane and converted to hydrophobic surface. The negatively charged CdSe NCs were adsorbed on the SWCNT surface by applying a negative gate bias. The measured photocurrent clearly demonstrates that CdSe NCs decorated SWCNT can be used for photodetector and solar cell that are operable over a wide range of wavelengths.
First-principles study of the structural and electronic properties of (100)Ge∕Ge(M)O2 interfaces (M=Al, La, or Hf)
Authors: Houssa M. , Pourtois G. , Caymax M. , Meuris M. , Heyns M. M.
Published: June 2008

The structural and electronic properties of (100)Ge∕Ge(M)O2 interfaces, with M=Al, La, or Hf, are investigated using density functional theory. When a Ge atom is substituted by a Hf atom in the GeOx (suboxide) interfacial layer, a Ge–Hf bond is formed due to the fivefold coordination of Hf in the GeOx matrix. The formation of this bond gives rise to a defect level in the upper part of the Ge energy band gap. On the other hand, the incorporation of Al or La in the interfacial layer results only in the formation of Al–O–Ge or La–O–Ge bonds at/near the interface due to the fourfold coordination of these metals in the GeOx matrix. This gives rise to a surface-state free Ge energy band gap. These findings highlight the advantage of lower coordinated metal oxides that tend to form germanate layers in contact with Ge for their potential use as gate stacks in high performance metal-oxide-semiconductor field effect transistors.
Mechanism and lifetime prediction method for hot-carrier-induced degradation in lateral diffused metal-oxide-semiconductor transistors
Authors: Chen Jone F. , Tian Kuen-Shiuan , Chen Shiang-Yu , Lee J. R. , Wu Kuo-Ming , Liu C. M.
Published: June 2008

The mechanism of hot-carrier-induced degradation in n-type lateral diffused metal-oxide-semiconductor (LDMOS) transistors is investigated. Experimental data reveal that hot-electron injection induced interface state generation in channel region is the main degradation mechanism. Since gate current (Ig) consists mainly of electron injection, Ig correlates well with device degradation. As a result, a lifetime prediction method based on Ig is presented for the purpose of projecting hot-carrier lifetime in LDMOS transistors.