bluuebunny/crossref_metadata_2025 huggingface dataset:
Two different classes of E2 ubiquitin-conjugating enzymes are required for the mono-ubiquitination of proteins and elongation by polyubiquitin chains with a specific topology
Authors: Windheim Mark , Peggie Mark , Cohen Philip
Published: January 2008

RING (really interesting new gene) and U-box E3 ligases bridge E2 ubiquitin-conjugating enzymes and substrates to enable the transfer of ubiquitin to a lysine residue on the substrate or to one of the seven lysine residues of ubiquitin for polyubiquitin chain elongation. Different polyubiquitin chains have different functions. Lys48-linked chains target proteins for proteasomal degradation, and Lys63-linked chains function in signal transduction, endocytosis and DNA repair. For this reason, chain topology must be tightly controlled. Using the U-box E3 ligase CHIP [C-terminus of the Hsc (heat-shock cognate) 70-interacting protein] and the RING E3 ligase TRAF6 (tumour-necrosis-factor-receptor-associated factor 6) with the E2s Ubc13 (ubiquitin-conjugating enzyme 13)–Uev1a (ubiquitin E2 variant 1a) and UbcH5a, in the present study we demonstrate that Ubc13–Uev1a supports the formation of free Lys63-linked polyubiquitin chains not attached to CHIP or TRAF6, whereas UbcH5a catalyses the formation of polyubiquitin chains linked to CHIP and TRAF6 that lack specificity for any lysine residue of ubiquitin. Therefore the abilities of these E2s to ubiquitinate a substrate and to elongate polyubiquitin chains of a specific topology appear to be mutually exclusive. Thus two different classes of E2 may be required to attach a polyubiquitin chain of a particular topology to a substrate: the properties of one E2 are designed to mono-ubiquitinate a substrate with no or little inherent specificity for an acceptor lysine residue, whereas the properties of the second E2 are tailored to the elongation of a polyubiquitin chain using a defined lysine residue of ubiquitin.
Post-translational modifications of adiponectin: mechanisms and functional implications
Authors: Wang Yu , Lam Karen S. L. , Yau Ming-hon , Xu Aimin
Published: January 2008

Adiponectin is an insulin-sensitizing adipokine with anti-diabetic, anti-atherogenic, anti-inflammatory and cardioprotective properties. This adipokine is secreted from adipocytes into the circulation as three oligomeric isoforms, including trimeric, hexameric and the HMW (high-molecular-mass) oligomeric complex consisting of at least 18 protomers. Each oligomeric isoform of adiponectin exerts distinct biological properties in its various target tissues. The HMW oligomer is the major active form mediating the insulin-sensitizing effects of adiponectin, whereas the central actions of this adipokine are attributed primarily to the hexameric and trimeric oligomers. In patients with Type 2 diabetes and coronary heart disease, circulating levels of HMW adiponectin are selectively decreased due to an impaired secretion of this oligomer from adipocytes. The biosynthesis of the adiponectin oligomers is a complex process involving extensive post-translational modifications. Hydroxylation and glycosylation of several conserved lysine residues in the collagenous domain of adiponectin are necessary for the intracellular assembly and stabilization of its high-order oligomeric structures. Secretion of the adiponectin oligomers is tightly controlled by a pair of molecular chaperones in the ER (endoplasmic reticulum), including ERp44 (ER protein of 44 kDa) and Ero1-Lα (ER oxidoreductase 1-Lα). ERp44 inhibits the secretion of adiponectin oligomers through a thiol-mediated retention. In contrast, Ero1-Lα releases HMW adiponectin trapped by ERp44. The PPARγ (peroxisome-proliferator-activated receptor γ) agonists thiazolidinediones selectively enhance the secretion of HMW adiponectin through up-regulation of Ero1-Lα. In the present review, we discuss the recent advances in our understanding of the structural and biological properties of the adiponectin oligomeric isoforms and highlight the role of post-translational modifications in regulating the biosynthesis of HMW adiponectin.
Chemokines and cancer: migration, intracellular signalling and intercellular communication in the microenvironment
Authors: O'Hayre Morgan , Salanga Catherina L. , Handel Tracy M. , Allen Samantha J.
Published: January 2008

Inappropriate chemokine/receptor expression or regulation is linked to many diseases, especially those characterized by an excessive cellular infiltrate, such as rheumatoid arthritis and other inflammatory disorders. There is now overwhelming evidence that chemokines are also involved in the progression of cancer, where they function in several capacities. First, specific chemokine–receptor pairs are involved in tumour metastasis. This is not surprising, in view of their role as chemoattractants in cell migration. Secondly, chemokines help to shape the tumour microenvironment, often in favour of tumour growth and metastasis, by recruitment of leucocytes and activation of pro-inflammatory mediators. Emerging evidence suggests that chemokine receptor signalling also contributes to survival and proliferation, which may be particularly important for metastasized cells to adapt to foreign environments. However, there is considerable diversity and complexity in the chemokine network, both at the chemokine/receptor level and in the downstream signalling pathways they couple into, which may be key to a better understanding of how and why particular chemokines contribute to cancer growth and metastasis. Further investigation into these areas may identify targets that, if inhibited, could render cancer cells more susceptible to chemotherapy.
An alternatively spliced exon links intermediate filaments to adhesions
Authors: Gimona Mario
Published: January 2008

Anchorage of the contractile actomyosin apparatus to the plasma membrane at discrete sites in muscle and non-muscle cells enables the transmission and conversion of force into work, such as muscle contraction and membrane deformation to regulate cell and tissue shape. Assembly, stabilization and turnover of adhesion sites are complex processes that involve structural components, a variety of signalling and adapter molecules, diverse kinases and phosphatases, and phospholipids. The dynamic turnover of adhesions also requires the frequent interaction with other filament systems of the cytoskeleton, in particular with microtubules. How the delivery and activation of all the required components is co-ordinated, however, remains to be fully understood. In the current issue of Biochemical Journal, Sun et al. provide evidence that a specific exon that is exclusively present in the α variant of the type IV intermediate filament protein synemin interacts directly with the focal adhesion protein vinculin in its active state. Interaction of adhesion components with intermediate filaments could serve as a general mechanism to regulate cell- and tissue-specific cytoskeleton-membrane attachment.
Role of adiponectin and PBEF/visfatin as regulators of inflammation: involvement in obesity-associated diseases
Authors: Tilg Herbert , Moschen Alexander R.
Published: January 2008

Obesity and obesity-related disorders play an important role in clinical medicine. Adipose tissue, with its soluble mediators called adipocytokines, has emerged as a major endocrine organ. These adipocytokines comprise many mediators such as adiponectin, PBEF (pre-B-cell-enhancing factor)/visfatin, leptin, resistin, retinol-binding protein-4 and others. They play major roles in key aspects of metabolism, such as insulin resistance, fatty acid oxidation, inflammation and immunity. Adiponectin, a prototypic adipocytokine, is of importance in the regulation of insulin resistance, as circulating levels are decreased in obesity and diseases associated with insulin resistance. Besides its major role in regulation of insulin sensitivity, recent evidence suggests potent anti-inflammatory functions for adiponectin. These effects are paralleled by other immune-regulatory properties, such as regulation of endothelial cell function. The in vitro effects of adiponectin have been corroborated by several studies demonstrating potent in vivo anti-inflammatory effects. Many other adipocytokines, such as PBEF/visfatin, leptin, resistin or retinol binding protein-4, are involved in the physiology and pathophysiology of adipocytes, adipose tissue and related diseases. PBEF/visfatin, another recently characterized adipocytokine, has been linked to several inflammatory disease states beyond insulin resistance, such as acute lung injury or inflammatory bowel diseases. It has been recognized for many decades that obesity is accompanied by an increase in cancer and potentially some immune-mediated diseases. Understanding this new exciting world of adipocytokines will be of importance in the development of novel therapies for obesity-associated diseases.
Pro-healing drug-eluting stents: a role for antioxidants?
Authors: Watt Jonathan , Wadsworth Roger , Kennedy Simon , Oldroyd Keith G.
Published: January 2008

Current strategies to lower the incidence of ISR (in-stent restenosis) following PCI (percutaneous coronary intervention) are aimed at modifying arterial healing after stent injury. This can impair endothelial recovery and render the vessel prone to acute thrombosis. As early restoration of endothelial integrity inhibits neointimal growth and thrombosis, alternative approaches which encourage this process may provide a more effective long-term result after PCI. Oxidative stress is enhanced after PCI and participates in the regulation of endothelial regeneration and neointimal growth. Moreover, evidence suggests antioxidants improve re-endothelialization and inhibit ISR. By promoting, rather than blocking, the healing process, antioxidant and other therapies may offer an alternative or additional approach over the antiproliferative approaches common to many current devices.
Combined anticoagulants ameliorate acute lung injury in sheep after burn and smoke inhalation
Authors: Enkhbaatar Perenlei , Esechie Aimalohi , Wang Jianpu , Cox Robert A. , Nakano Yoshimitsu , Hamahata Atsumori , Lange Matthias , Traber Lillian D. , Prough Donald S. , Herndon David N. , Traber Daniel L.
Published: January 2008

Burn and smoke inhalation-related multiple organ dysfunction is associated with a severe fall in the plasma concentration of antithrombin. Therefore the aim of the present study was to test the hypothesis that intravenous administration of recombinant human antithrombin in combination with aerosolized heparin will ameliorate acute lung injury in sheep exposed to cutaneous burn and smoke inhalation. Sheep were prepared operatively for study and, 7 days post-surgery, sheep were given a cutaneous burn (40% of total body surface area, third-degree burn) and insufflated with cotton smoke (48 breaths, <40 °C) under halothane anaesthesia. After injury, sheep were placed on a ventilator and resuscitated with Ringer's lactate solution. The animals were divided into three groups: sham group (non-injured and non-treated; n=6), saline group (injured and received saline; n=6) and rhAT.iv.+Hep group [injured and treated with rhAT (recombinant human antithrombin) and heparin; n=6]. In the rhAT.iv.+Hep group, rhAT was infused continuously for 48 h starting 1 h post-injury with a dose of 0.34 mg·h−1·kg−1 of body weight and heparin (10000 units) was aerosolized every 4 h starting at 1 h post-injury. The experiment lasted 48 h. Haemodynamics were stable in sham group, whereas the saline-treated sheep developed multiple signs of acute lung injury, including decreased pulmonary gas exchange, increased inspiratory pressures, extensive airway obstruction and increased pulmonary oedema. These pathological changes were associated with a severe fall in plasma antithrombin concentration, lung tissue accumulation of leucocytes and excessive production of NO. Treatment of injured sheep with anticoagulants attenuated all of the pulmonary pathophysiology observed. In conclusion, the results provide definitive evidence that anticoagulant therapy may be a novel and effective treatment tool in the management of burn patients with concomitant smoke inhalation injury.
Mechanism of the endothelium-dependent relaxation evoked by a grape seed extract
Authors: Edirisinghe Indika , Burton-Freeman Britt , Tissa Kappagoda C.
Published: January 2008

GSEs (grape seed extracts) which contain polyphenolic compounds cause an endothelium-dependent relaxation of blood vessels. The aim of the present study was to examine the mechanisms involved in this response. A well-characterized GSE was applied to rabbit aortic rings suspended in organ baths containing Krebs–Henseleit buffer maintained at 37 °C. In aortic rings pre-contacted with noradrenaline (norepinephrine), the extract produced a dose-dependent relaxation. The maximum relaxations elicited by the extract (71.9±1.0%) were similar to those elicited by acetylcholine (64.2±1.5%) (n=12 for each). As expected, the relaxations were abolished by removal of the endothelium and by prior incubation with L-NAME (NG-nitro-L-arginine methyl ester), confirming the essential role of eNOS (endothelial NO synthase) in the response. The responses to the GSE were also abolished by incubation with wortmannin and LY294002, which are inhibitors of PI3K (phosphoinositide 3-kinase). These compounds had no effect on the responses to acetylcholine. Using immunoblotting, we also demonstrated that the GSE induced the phosphorylation of both Akt and eNOS in HUVECs (human umbilical vein endothelial cells). Finally, the extract was modified by methylation of the hydroxy groups in the polyphenolic groups and was applied to the aortic rings. The modified extract failed to cause a relaxation. Taken together, these findings suggest that the endothelium-dependent relaxation induced by the GSE was mediated by activation of the PI3K/Akt signalling pathway through a redox-sensitive mechanism, resulting in phosphorylation of eNOS.
Altered protein metabolism following coronary artery bypass graft (CABG) surgery
Authors: Caso Giuseppe , Vosswinkel James A. , Garlick Peter J. , Barry Mohamed K. , Bilfinger Thomas V. , Mcnurlan Margaret A.
Published: January 2008

The aim of the present study was to investigate the acute effect of CABG (coronary artery bypass graft) surgery on the rates of synthesis of muscle protein, the positive acute-phase protein fibrinogen and the negative acute-phase protein albumin. Synthesis rates of muscle protein, fibrinogen and albumin were measured simultaneously before and 4 h after the end of surgery from the incorporation of L-[2H5]phenylalanine (given at 43 mg/kg of body weight) in 12 patients undergoing CABG surgery. Surgery was performed either with the use of extracorporeal circulation with cardiopulmonary bypass (on-pump; n=5) or with the beating heart procedure without cardiopulmonary bypass (off-pump; n=7). Post-surgical muscle protein fractional synthesis rates were decreased by 36±6.5% compared with pre-surgical values (1.59±0.10 compared with 0.97±0.08%/day respectively; P<0.001). In contrast, the synthesis rates of both fibrinogen (36±4 compared with 100±11 mg·day−1·kg−1 of body weight; P<0.0001) and albumin (123±12 compared with 178±19 mg·day−1·kg−1 of body weight; P<0.001) were both significantly increased after surgery. No significant differences were found between surgery performed with or without cardiopulmonary bypass. In conclusion, the results demonstrate that CABG surgery has a profound effect on protein metabolism, with a differential response of protein synthesis in muscle and liver.
Protective effect of female gender on the development of albuminuria in a polygenetic rat model is enhanced further by replacement of a major autosomal QTL
Authors: Schulz Angela , Schlesener Maria , Weiss Judith , Hänsch Jonna , Wendt Norbert , Kossmehl Peter , Grimm Daniela , Vetter Roland , Kreutz Reinhold
Published: January 2008

Clinical and experimental studies indicate that the progression of renal disease is faster in males than females. These observations are corroborated by a sexual dimorphism observed in the polygenetic MWF (Munich Wistar Frömter) rat model. The age-dependent spontaneous progression of increased UAE (urinary albumin excretion) in male MWF rats is influenced by multiple QTLs (quantitative trait loci). In contrast, female MWF rats only develop a slight increase in UAE, while the role of genetic factors for this phenotype is unknown. In the present study, we show that, compared with resistant SHRs (spontaneously hypertensive rats), both male and female MWF rats develop a significant increase in UAE at 24 weeks of age (P<0.0001), although blood pressures were lower compared with SHRs (P<0.0001). UAE was significantly higher in male (7-fold) compared with female MWF rats (162.6±15.9 compared with 24.0±5.5 mg/24 h respectively; P<0.0001), and only male MWF rats developed significant glomerulosclerosis and tubulointerstitial damage in the kidney (P<0.0001). To test the role of genetic factors in the development of low grade albuminuria in female MWF rats, we analysed the role of a major UAE QTL on rat chromosome 6. To this end, we analysed a consomic MWF-6SHR strain in which chromosome 6 from SHRs was introgressed into the MWF rat background. Time course analysis of UAE in females indicated that the small increase in UAE in MWF rats was fully suppressed by exchange of rat chromosome 6. Thus, taken together with previous studies in males, we show that RNO6 protects against the increase in albuminuria with age in both female and male MWF rats.
The Geometric Phase Shows up in Chemical Reactions
Authors: Levi Barbara Goss
Published: January 2008

One of the simplest chemical exchange reactions involves a system of three hydrogen atoms: H+ H2→H2+H. Surely, chemists have felt, one should be able to calculate the cross sections for this reaction from first principles. But the computations have not been easy. Only in the last six years or so have theorists, aided by efficient methodologies and access to supercomputers, been able to predict the cross sections in sufficient detail for comparison with experiments, which themselves have evolved in precision. The agreement has been good—well, almost. Small discrepancies, especially at higher total energies, stubbornly refused to yield to adjustments in either the calculations or the experiments. Now Yi-Shuen Mark Wu and Aron Kuppermann of Caltech have erased these pesky discrepancies by including a topological effect known as the geometric phase. Michael Berry (University of Bristol) has called attention to the presence of this phase, which now bears his name, in a wide variety of physical systems. (See Berry's article in PHYSICS TODAY, December 1990, page 34.)
New Evidence Confirms Old Predictions of Retarded Forces
Authors: Levi Barbara Goss
Published: January 2008

Some of the more subtle predictions of quantum mechanics have had to wait decades before experiments were capable of validating them. One of these is the so-called retarded force between charges that are so far apart that it takes a relatively long time for a photon to travel between them. (See the article by Larry Spruch in PHYSICS TODAY, November 1986, page 37.) In the 1940s Hendrik B. G. Casimir and D. Polder (then at the scientific laboratory of N. V. Philips's Gloeilampenfabriken in Eindhoven, the Netherlands) analyzed interactions affected by the finite speed of light. They found that the van der Waals potential between two atoms, which goes as r−6, becomes a potential that varies as r−7 when the atoms are separated by distances greater than a few hundred Bohr radii. A related prediction is that the interaction between a neutral atom and a conducting wall changes from an r−3 to an r−4 potential when the atom is far enough from the wall. Casimir subsequently formulated an expression for the force between two conducting plates which is now known as the Casimir force
STM Rounds up Electron Waves at the QM Corral
Authors: Collins Graham P.
Published: January 2008

Everyone who has completed an elementary quantum mechanics course has seen plots of solutions of the Schrödinger equation for the archetypal “particle in a box.” Now IBM researchers have used scanning tunneling microscopy to image the rippled density of states of electrons inside a “corral” built with a few dozen carefully positioned iron atoms on a copper surface. (See the cover of this issue.) The spectacular results closely match theoretical models of the system.
IUPAC/IUPAP Committee Mediates Custody Battle Over Heavy Elements
Authors: Levi Barbara Goss
Published: January 2008

Unlike babies, which are usually named at birth, a number of heavy elements have remained anonymous even though some are nearly 30 years old. These nameless orphans have been the objects of bitter custody battles: Three major research groups—located at the University of California at Berkeley, the Joint Institute for Nuclear Research in Dubna, Russia, and the Laboratory for Heavy Ion Research (GSI) in Darmstadt, Germany—have competed intensely for years to produce the heavy elements and have filed conflicting claims for discovery. But given the difficult nature of the experiments on such short-lived isotopes, it hasn't always been clear which group has really produced a given element
Researchers Cook Up a Baked Alaska in Superfluid Helium-3
Authors: Collins Graham P.
Published: January 2008

The conventional recipe for a baked Alaska calls for meringue, solid ice cream and a moderate degree of culinary skill. The baked Alaskas recently observed by Peter Schiffer, Douglas Osheroff and coworkers at Stanford University involve the superfluid phases of helium-3, sample cells with ultrasmooth walls and a sprinkling of cosmic rays. Their results strongly support the “baked Alaska” model that was devised to solve the long-standing puzzle of how the B phase of superfluid He3 can possibly nucleate in a sample of A phase. Also, their techniques for the first time allow the study of an anisotropic BCS superfluid in the lowtemperature limit in the absence of a strong magnetic field.
Arctic Measurements Indicate the Chilly Prospect of Ozone Depletion
Authors: Levi Barbara Goss
Published: January 2008

The North Pole warmed just in time this spring to avoid a possibly significant depletion of ozone. That conclusion is one outcome of the second Airborne Arctic Stratospheric Expedition, which reported on its findings at the end of April. Earlier, in the first days of February, the participating scientists had released some preliminary results because they were alarmed at seeing very high levels of chlorine monoxide, a reactive chlorine compound associated with ozone destruction. As shown in the figure below, which is based on satellite data, the levels and extent of CLO this January were comparable to those seen during the winter months in the Antarctic, where an “ozone hole” is known to develop at that time.
Symmetry breaking in benzene and larger aromatic molecules within generalized valence bond coupled cluster methods
Authors: Lawler Keith V. , Beran Gregory J. O. , Head-Gordon Martin
Published: January 2008

The origin of symmetry breaking (SB) in benzene in generalized valence bond methods is investigated within a coupled cluster formalism that correlates all valence electrons. Retention of a limited number of pair correlation amplitudes (as in the perfect- and imperfect-pairing models) that incompletely describes interpair correlations leads to symmetry breaking as the orbitals and amplitudes are optimized. Local correlation models that are exact for one, two, and three interacting pairs at the doubles excitation level are compared against the exact pair correlation treatment, which correlates four interacting pairs at once in the connected double substitution operator. For simplicity, this comparison is performed with a second-order model of electron correlation, which is reasonably faithful to the infinite-order result. The significant SB known for the one-pair model (perfect pairing) is not eliminated at the two-pair level, but is virtually eliminated at the three-pair level. Therefore, a tractable hybrid model is proposed, which combines three-pair correlations at the second-order level and infinite-order treatment for the strong imperfect-pairing correlations involving one and two-pair correlations. This model greatly reduces SB in benzene and larger delocalized π systems such as naphthalene and the phenalenyl cation and anion. The resulting optimized orbitals are localized in the σ space but exhibit significant delocalization in the π space. This means that correlation effects associated with different resonance structures are treated in a more balanced way than if the π orbitals localize, leading to reduced SB.
Bifurcations and chaos in register transitions of excised larynx experiments
Authors: Tokuda Isao T. , Horáček Jaromir , Švec Jan G. , Herzel Hanspeter
Published: January 2008

Experimental data from an excised larynx are analyzed in the light of nonlinear dynamics. The excised larynx provides an experimental framework that enables artificial control and direct observation of the vocal fold vibrations. Of particular interest in this experiment is the coexistence of two distinct vibration patterns, which closely resemble chest and falsetto registers of the human voice. Abrupt transitions between the two registers are typically accompanied by irregular vibrations. Two approaches are presented for the modeling of the excised larynx experiment; one is the nonlinear predictive modeling of the experimental time series and the other is the biomechanical modeling (three-mass model) that takes into account basic mechanisms of the vocal fold vibrations. The two approaches show that the chest and falsetto vibrations correspond to two coexisting limit cycles, which jump to each other with a change in the bifurcation parameter. Irregular vibrations observed at the register jumps are due to chaos that exists near the two limit cycles. This provides an alternative mechanism to generate chaotic vibrations in excised larynx experiment, which is different from the conventionally known mechanisms such as strong asymmetry between the left and right vocal folds or excessively high subglottal pressure.
Vapor-phase nucleation of individual CdSe nanostructures from shape-engineered nanocrystal seeds
Authors: Fasoli A. , Pisana S. , Colli A. , Carbone L. , Manna L. , Ferrari A. C.
Published: January 2008

We investigate the vapor-phase nucleation of CdSe nanostructures on nanocrystals seeds of different shapes. The growth dynamics is assessed by transmission electron microscopy, following the evolution of the same nanocrystals prior and after the deposition process. We prove that individual nanocrystals can sustain the growth of single nanowires and determine their final morphology. Straight or branched nanowires are obtained from spherical or tetrapod-shaped nanocrystals, respectively. When tetrapod-shaped nanocrystals are used, we also find that their original shape and orientation are mostly preserved upon further growth.
Electron transport of nanotube-based gas sensors: An ab initio study
Authors: Sadrzadeh Arta , Farajian Amir A. , Yakobson Boris I.
Published: January 2008

The effect of physisorption of NO2 gas molecules on quantum transport properties of semiconducting carbon nanotubes is studied using ab initio calculations and Green function formalism. The results show that the conductance change is mainly due to the electric dipole moment of NO2. It is also shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance toward lower energies. This suggests that physisorption of NO2 will result in a decrease (increase) in conductance of p-type (n-type) nanotubes with Fermi energies close to the edge of valence and conduction band.
X-ray and ion measurements in laser produced plasma from gold-copper alloy targets
Authors: Chaurasia S. , Munda D. S. , Murali C. G. , Gupta N. K. , Dhareshwar L. J.
Published: January 2008

Enhancement in x-ray emission from laser plasmas produced from an alloy of gold and copper (Au 0.43+Cu 0.57 atomic composition) has been observed in a narrow spectral region of 1.5–3.9Å. X-ray emission is observed to be as high as six to nine times as compared to pure copper and 1.5 to 1.8 times as compared to pure gold targets. In these experiments, a single pulse from a Nd:glass laser (λ=1.06μm) having an energy up to 2J and 500ps pulse duration was used to obtain a focused intensity of 1013–1014W∕cm2 on the targets. The results are explained on the basis of enhanced group Rosseland opacity (Rosseland mean over the spectral range under consideration) for the Au–Cu alloy target as compared to either of the pure targets.
A particle-in-cell plus Monte Carlo study of plasma-induced damage of normal incidence collector optics used in extreme ultraviolet lithography
Authors: Wieggers R. C. , Goedheer W. J. , Akdim M. R. , Bijkerk F. , Zegeling P. A.
Published: January 2008

We present a kinetic simulation of the plasma formed by photoionization in the intense flux of an extreme ultraviolet lithography (EUVL) light source. The model is based on the particle-in-cell plus Monte Carlo approach. The photoelectric effect and ionization by electron collisions are included. The time evolution of the low density argon plasma is simulated during and after the EUV pulse and the ion-induced sputtering of the coating material of a normal incidence collector mirror is computed. The relation between the time and position at which the ions are created and their final energy is studied, revealing how the evolution and the properties of the sheath influence the amount of sputtered material. The influence of the gas pressure and the source intensity is studied, evaluating the behavior of Ar+ and Ar2+ ions. A way to reduce the damage to the collector mirror is presented.
Electron mobility of 4,7-diphyenyl-1,10-phenanthroline estimated by using space-charge-limited currents
Authors: Khan M. A. , Xu Wei , Khizar-ul-Haq  , Bai Yu , Jiang X. Y. , Zhang Z. L. , Zhu W. Q. , Zhang Z. L. , Zhu W. Q.
Published: January 2008

The electron mobility of 4,7-diphyenyl-1,10-phenanthroline (BPhen) at various thicknesses (50–300nm) has been estimated by using space-charge-limited current measurements. The measured bulk mobility is in excellent agreement with results from time-of-flight method. It has been observed that the electron mobility of BPhen approaches its true value when the thickness is more than 150nm. The estimated electron mobility of BPhen at 300nm is found to be 3.4×10−4cm2∕Vs (at 0.3MV∕cm) with weak dependence on electric field. For thickness typical of organic light-emitting devices, the electron mobility of BPhen is also investigated.

At the request of the authors, this article is being retracted effective 31 May 2011.
Comparative structural and electrical analysis of NiO and Ti doped NiO as materials for resistance random access memory
Authors: Lee M. J. , Park Y. , Ahn S. E. , Kang B. S. , Lee C. B. , Kim K. H. , Xianyu W. X. , Yoo I. K. , Lee J. H. , Chung S. J. , Kim Y. H. , Lee C. S. , Choi K. N. , Chung K. S.
Published: January 2008

In order to investigate the mechanism behind bistable resistance switching in NiO thin films, we have done detailed x-ray photon spectroscopy (XPS) and x-ray diffraction Analysis (XRD) on NiO and Ti doped NiO samples fabricated under various conditions. We discovered that a high initial resistivity was required for samples to undergo bistable resistance switching, and the presence of metallic Ni content in these samples was determined by XPS. XRD data also showed that NiO grown with a relative (200) orientation was preferred over those grown with relative (111) orientation.
A model for self-defocusing in laser drilling of polymeric materials
Authors: Zhang Chong , Quick Nathaniel R. , Kar Aravinda
Published: January 2008

A numerical thermal model is presented for laser microvias drilling in multilayer electronic substrates with Nd:YAG (YAG denotes yttrium aluminum garnet) and CO2 lasers. Such substrates have different optical properties such as the refractive index and absorption coefficient at these two laser wavelengths, resulting in different drilling mechanisms. Since the skin depth of the polymer is large for both the lasers, volumetric heating is considered in the model. As soon as a small cavity is formed during the drilling process, the concave curvature of the drilling front acts as a concave lens that diverges the incident laser beam. This self-defocusing effect can greatly reduce the drilling speed as predicted by the model. This effect makes the refractive index of the substrate at different wavelengths an important parameter for laser drilling. The model was used to calculate the laser ablation thresholds which were found to be 8 and 56J∕cm2 for the CO2 and Nd:YAG lasers respectively. Due to the expulsion of materials because of high internal pressures in the case of Nd:YAG laser microvia drilling, the ablation threshold may be far below the calculated value. A particular laser beam shape, such as pitch fork, was found to drill better holes than the Gaussian beam.
High doping level in Mg-doped GaN layers grown at low temperature
Authors: Dussaigne A. , Damilano B. , Brault J. , Massies J. , Feltin E. , Grandjean N.
Published: January 2008

We have studied the properties of Mg-doped GaN epilayers grown by molecular beam epitaxy (MBE) with ammonia as nitrogen source. GaN p-n homojunctions has been developed to determine the optoelectronic characteristics of the junctions as a function of the p-type GaN growth conditions. It is shown that the electrical characteristics strongly depend on the Mg flux and the growth temperature. As a result, the junction characteristics have been drastically improved and state of the art MBE-grown p-type layers have been obtained: the hole concentration, the mobility, and the resistivity are 1×1018cm−3, 9cm2∕Vs, and 0.75Ωcm, respectively. These characteristics lead to an increase of the homojunction light emitting diode (LED) optical output power by two orders of magnitude. To further assess the quality of these MBE-grown p-type layers, we have prepared a hybrid LED which consists of an InGaN∕GaN quantum well active structure grown by metal organic vapor phase epitaxy followed by a p-type region grown by MBE. An optical power in the milliwatt range at 20mA is demonstrated confirming thereby the quality of low temperature MBE-grown p-type layers.
Physical properties and efficiency of GaNP light emitting diodes
Authors: Chamings J. , Ahmed S. , Sweeney S. J. , Odnoblyudov V. A. , Tu C. W.
Published: January 2008

Ga N P ∕ Ga P is promising for yellow-amber-red light emitting diodes (LEDs). In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk GaP∕GaN0.006P0.994∕GaP LED structures are presented. Below ∼110K, emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of +1.6meV∕kbar, substantially lower than the Γ band gap of GaP (+9.5meV∕kbar). Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the X minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure.
Study of light distribution through liquid crystal (LC) lens arrays
Authors: Hikmet R. A. M. , van Bommel T. , Kraan T. C.
Published: January 2008

Refractive index gradient formation in liquid crystal cells during the application of an electric field across patterned electrodes was studied. The cells were characterized by measuring the intensity profile of a parallel beam of light passing through the cells. Most of the measurements were performed using transparent electrodes comprising periodic straight-line patterns with a conducting linewidth of 4μm and various pitches in the range of 34–54μm. The intensity profiles through such cells were studied and it was observed that the intensity showed oscillations as a function of angle. Director profiles were calculated in order to estimate the effective refractive index distribution within the cells. Using this input in theoretical models based on wave theory as well as geometrical optics, intensity profiles could be estimated. The limits of each theory were illustrated and it was shown that the oscillations in the intensity profile could be explained by the wave theory. The effects of the orientation of the molecules with respect to the electrode lines and cell surfaces and its influence on twist of the molecules leading to depolarization of light were investigated. Various other parameters such as the pitch and the cell thickness on the refractive index gradient formation and the resulting light distribution through the cells were also studied.
Magnetoelectric coupling in CoFe2O4∕SrRuO3∕Pb(Zr0.52Ti0.48)O3 heteroepitaxial thin film structure
Authors: Zhang J. X. , Dai J. Y. , Chow C. K. , Sun C. L. , Lo V. C. , Chan H. L. W.
Published: January 2008

Epitaxial magnetoelectric Pb(Zr0.52Ti0.48)O3∕SrRuO3∕CoFe2O4 composite thin films are fabricated on SrTiO3 single crystal substrate by pulsed-laser deposition. x-ray diffraction study reveals their crystalline structure and epitaxial relationship, which is cubic on cubic without in-plane rotation. The good dielectric, ferroelectric, and magnetic properties for the heteroepitaxial films are obtained simultaneously under room temperature, and the magnetoelectric coupling effect is manifested by the magnetic-field-dependent ferroelectric characteristics and spectroscopic dielectric constant.
Epitaxial ordering of a perylenetetracarboxylic diimide-melamine supramolecular network driven by the Au(111)-(22×3) reconstruction
Authors: Silly Fabien , Shaw Adam Q. , Briggs G. A. D. , Castell Martin R.
Published: January 2008

Substrate mediated ordering and intermolecular interactions are used to create a long-range supramolecular network of perylenetetracarboxylic diimide and melamine on a reconstructed Au(111)-(22×3) surface. Scanning tunneling microscopy reveals that the network is composed of a succession of double width honeycomb cell rows separated by a more closely packed row of parallelograms. This periodicity of the supramolecular configuration matches that of the reconstructed gold substrate allowing an epitaxial relationship between network and substrate reconstruction.
Fast photorefractive self-focusing in InP:Fe semiconductor at infrared wavelengths
Authors: Wolfersberger Delphine , Khelfaoui Naïma , Dan Cristian , Fressengeas Nicolas , Leblond Hervé
Published: January 2008

Photorefractive beam self-trapping is investigated in InP:Fe and is shown to occur within tens of microseconds after beam switch on. This fast response time is predicted by an analytical theoretical interpretation based on a simple photorefraction model which suggests buildups in a time range consistent with experiments.
Dual-layer patterned media “ledge” design for ultrahigh density magnetic recording
Authors: Lomakin Vitaliy , Choi Richard , Livshitz Boris , Li Shaojing , Inomata Akihiro , Bertram H. Neal
Published: January 2008

Patterned media elements comprising coupled magnetically hard and soft sections of different horizontal size, referred to as ledge elements, are characterized by several unique properties. These elements allow for remarkably reduced reversal fields, which are an order of magnitude below the Stoner-Wohlfarth limit. They also allow for precessional reversal to occur for practical field rise times (100–200ps), which are two orders of magnitude larger than those in the case of homogeneous elements (∼2ps). These attractive properties are obtained even for elements of small height (4–8nm). Patterned media implementing such ledge elements can allow for recording densities above 10Tbit∕in2.
The Christiansen effect in terahertz time-domain spectra of coarse-grained powders
Authors: Franz Morten , Fischer Bernd M. , Walther Markus
Published: January 2008

Spectral distortions are commonly observed in terahertz transmission spectra of ground substances immersed in a transparent host medium. This effect originates from scattering due to the index contrast between the grains and diluent. A phenomenological expression quantitatively accounts for the scattering induced attenuation and the phase delay experienced by the electric field transmitted through the sample. Based on the knowledge of the refractive indices of the sample and the host material, we present a procedure to eliminate the scattering contribution from the absorption spectra.
Photonic crystal nanolaser monolithically integrated with passive waveguide for effective light extraction
Authors: Nozaki Kengo , Watanabe Hideki , Baba Toshihiko
Published: January 2008

We recently reported room-temperature continuous-wave operation in a GaInAsP photonic crystal slab nanolaser. In this letter, we demonstrate effective light extraction from the nanolaser monolithically integrated with a passive waveguide by using a GaInAsP butt-joint regrowth technique. Theoretically, the extraction efficiency through the waveguide was calculated to be 80% for the optimum design of the coupling system of the nanolaser and the waveguide. In the experiment, we evaluated a differential quantum efficiency of 4%, which was degraded mainly due to the detection loss of the output light.
Ohmic contact formation on n-type Ge
Authors: Lieten R. R. , Degroote S. , Kuijk M. , Borghs G.
Published: January 2008

Severe Fermi level pinning at the interface between n-Ge and a metal leads to the formation of a Schottky barrier, almost independent on the metal work function. Therefore, it seems impossible to form metal Ohmic contacts on moderately, n-type doped Ge layers. For p-type Ge, the Fermi level pinning works opposite: all metal contacts show Ohmic behavior. This fixed behavior can be altered by the introduction of a thin Ge3N4 layer. Ge3N4 seems effective in reducing Fermi level pinning and, therefore, allows the formation of Ohmic contacts on n-type Ge and a rectifying contact on p-type Ge.
ac thermal imaging of nanoheaters using a scanning fluorescent probe
Authors: Samson B. , Aigouy L. , Löw P. , Bergaud C. , Kim B. J. , Mortier M.
Published: January 2008

Using a fluorescent particle glued at the end of a sharp tip, we observe the heating of a 200nm wide nickel nanoheater run by an alternating electrical current. The images clearly show the heating of the nickel structure, as well as the lateral heat diffusion in the dielectric layers underneath. By monitoring the fluorescence changes as the tip approaches the nanoheater, we have estimated the relative importance of the different heat transfer mechanisms between the device and the fluorescent particle. It is shown that, for the investigated structures, heat transfer occurs mainly by direct contact between the probe and the surface.
Spin-orbit splitting of a hydrogenic donor impurity in GaAs∕GaAlAs quantum wells
Authors: Li Shu-Shen , Xia Jian-Bai
Published: January 2008

The electronic states of a hydrogenic donor impurity in GaAs∕GaAlAs quantum wells are investigated theoretically in the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling. The splits of electron energy levels are calculated. The results show that (1) the split energy of the excited state is larger than that of the ground state; (2) the split energy peak appears as the GaAs well width increases from zero; and (3) the maximum split energy reaches about 1.6meV. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices.
Modeling boron diffusion gettering of iron in silicon solar cells
Authors: Haarahiltunen A. , Talvitie H. , Savin H. , Yli-Koski M. , Asghar M. I. , Sinkkonen J.
Published: January 2008

In this paper, a model is presented for boron diffusion gettering of iron in silicon during thermal processing. In the model, both the segregation of iron due to high boron doping concentration and heterogeneous precipitation of iron to the surface of the wafer are taken into account. It is shown, by comparing simulated results with experimental ones, that this model can be used to estimate boron diffusion gettering efficiency of iron under a variety of processing conditions. Finally, the application of the model to phosphorus diffusion gettering is discussed.
Mapping Dark Matter with Gravitational Lenses
Authors: Tyson Anthony
Published: January 2008

Through the long-range force of gravity, mass controls the evolution of the universe. Studies of the internal motion of large, gravitationally bound systems such as galaxies and clusters of galaxies have already shown us, rather convincingly, that the mass in these systems is dominated by some form of matter that is not luminous at any wavelength from radio to x ray. (See the article by Scott Tremaine in PHYSICS TODAY, February, page 28.)
The Future of Solid-State Electronics
Authors: Keyes Robert W.
Published: January 2008

The growth of commerce around the end of the 16th century created a need for large amounts of numerical calculation. the increasing understanding of astronomical phenomena around the same time also depended on accurate computation. the difficulty of accurately performing large amounts of tedious numerical work by hand stimulated Leibniz, Pascal and others to invent mechanical adding and multiplying machines in the 17th century. (See figure 1.) the speed and complexity of mechanical computation were limited by inertia, friction, size and the difficulty of transmitting information very far. the development of electrical technology led to the introduction of electrical components in peripheral parts of computing machines, such as motors in place of hand cranks. Major improvements in performance, however, had to await the electrical representation of information
Micromechanical Models of the Cochlea
Authors: Allen Jont B. , Neely Stephen T.
Published: January 2008

Understanding human perception is at the forefront of scientific research goals today. The development of robots, virtual reality, speech coders and speech recognition devices depends on a good understanding of how we hear. The cochlea is the part of the inner ear that converts acoustic signals to the neural code that conveys auditory information to the brain. Modeling the function of the cochlea has been an active area of research since the development of the digital computer, yet several mysteries remain.
Optical Probes in the Quantum Hall Regime
Authors: Nurmikko Arto , Pinczuk Aron
Published: January 2008

Semiconductor nanostructures in which mobile electrons reside in a specific spatial region, such as a thin quantum well formed by heterojunction layers on the order of 100 Å in thickness, constitute a particularly striking physical system. The mobile electrons in such a system form a “two-dimensional electron gas.” In a uniform semiconductor electrons scatter off the ionized donor dopants, but in a two-dimensional electron gas the electrons can be separate from the dopants and enjoy extraordinarily long mean free paths (many micrometers) at cryogenic temperatures. In the past dozen years or so, this unique property has provided an enormously rich field for the study of electron transport phenomena, ranging from ballistic motion in small device structures to many-electron correlations in strong magnetic fields
Nonlinear Optics in Quanutm-Confined Structures
Authors: Chemla Daniel S.
Published: January 2008

Nonlinear optical effects arise when one applies to a material system optical fields that are on the order of or larger than the atomic fields that exist within the system. Quantum size effects appear when the dimensions of a system become comparable to or even smaller than the natural length scale governing its quantum mechanics. Much recent progress has resulted from the combination of these two very productive areas of physics. Because of advances in semiconductor and laser technologies, it is now possible to apply very intense, ultrashort pulses of light to nanometer-scale semiconductor heterostructures. These conditions produce many new and exciting effects. This article aims to give the reader a flavor of the status of this quickly evolving field of research, with a special emphasis on the most novel and unexpected results.