bluuebunny/crossref_metadata_2025 huggingface dataset:
Stellar black holes: Cosmic history and feedback at the dawn of the universe
Authors: Mirabel I. Felix
Published: February 2011

Significant historic cosmic evolution for the formation rate of stellar black holes is inferred from current theoretical models of the evolution of massive stars, the multiple observations of compact stellar remnants in the near and distant universe, and the cosmic chemical evolution. The mean mass of stellar black holes, the fraction of black holes/neutron stars, and the fraction of black hole high mass X-ray binaries (BH-HMXBs)/solitary black holes increase with redshift. The energetic feedback from large populations of BH-HMXBs form in the first generations of star burst galaxies has been overlooked in most cosmological models of the reionization epoch of the universe. The powerful radiation, jets, and winds from BH-HMXBs heat the intergalactic medium over large volumes of space and keep it ionized until AGN take over. It is concluded that stellar black holes constrained the properties of the faintest galaxies at high redshifts. I present here the theoretical and observational grounds for the historic cosmic evolution of stellar black holes. Detailed calculations on their cosmic impact are presented elsewhere (Mirabel, Dijkstra, Laurent, Loeb, & Pritchard 2011).
The stability of astrophysical jets
Authors: Hardee Philip E.
Published: February 2011

Jets are produced by young stellar objects (YSOs), by black hole binary star system “microquasars” (μQSOs), by active galactic nuclei (AGN), are associated with neutron stars and pulsar wind nebulae (PWNe), and are thought responsible for the gamma-ray bursts (GRBs). An understanding of these outflows must include how they are launched and collimated into jets, and how they propagate to large distances. Jets be they Poynting flux and/or kinetic flux dominated are current driven (CD) and/or Kelvin-Helmholtz (KH) velocity shear driven unstable. Here I present some of the work that is leading to a better understanding of the properties required for the observed relative stability of astrophysical jets.
The X-ray burster 4U 1608-522 as seen by JEM-X onboard INTEGRAL
Authors: Sánchez-Fernández Celia , Kuulkers Erik
Published: February 2011

We present here and overview of the results of a systematic search of Type-I X-ray bursts in the light curves of the transient, atoll system 4U 1608–522 as seen by JEMX onboard INTEGRAL.
Brown dwarf jets: Investigating the universality of jet launching mechanisms at the lowest masses
Authors: Whelan Emma Teresa , Bacciotti Francesca , Ray Tom , Dougados Catherine
Published: February 2011

Recently it has become apparent that proto-stellar-like outflow activity extends to the brown dwarf (BD) mass regime. While the presence of accretion appears to be the common ingredient in all objects known to drive jets fundamental questions remain unanswered. The more prominent being the exact mechanism by which jets are launched, and whether this mechanism remains universal among such a diversity of sources and scales. To address these questions we have been investigating outflow activity in a sample of protostellar objects that differ considerably in mass and mass accretion rate. Central to this is our study of brown dwarf jets. To date Classical T Tauri stars (CTTS) have offered us the best touchstone for decoding the launching mechanism. Here we shall summarise what is understood so far of BD jets and the important constraints observations can place on models. We will focus on the comparison between jets driven by objects with central mass <0.1M⊙ and those driven by CTTSs. In particular we wish to understand how the the ratio of the mass outflow to accretion rate compares to what has been measured for CTTSs.
Astrophysical outflows simulated by laser-driven plasma jets
Authors: Michaut C. , Gregory C. D. , Loupias B. , Falize E. , Ravasio A. , Dizière A. , Vinci T. , Koenig M. , Bouquet S.
Published: February 2011

Within the framework of laboratory astrophysics, we form a qualified multidisciplinary group in radiative hydrodynamics. Since 10 years, we have developed laboratory experiments as radiative shocks and plasma jets in connection to astrophysics. Such laboratory experiments provide a unique opportunity to validate models and numerical schemes introduced in radiative hydrodynamics codes. Here we summarize our experimental researches about plasma jets. Laboratory astrophysical experiments have been performed using LULI2000 (France), VULCAN (UK) and GEKKO XII (Japan) intense lasers. The goal of these experiments is to investigate some of the complex features of jets from Young Stellar Objects (YSO), and in particular its interaction with the interstellar medium (ISM).
Should health authorities offer risk-sharing contracts to pharmaceutical firms? A theoretical approach
Authors: Antonanzas Fernando , Juarez-Castello Carmelo , Rodriguez-Ibeas Roberto
Published: February 2011

In this paper, we characterise the risk-sharing contracts that health authorities can design when they face a regulatory decision on drug pricing and reimbursement in a context of uncertainty. We focus on two types of contracts. On the one hand, the health authority can reimburse the firm for each treated patient regardless of health outcomes (non risk-sharing). Alternatively, the health authority can pay for the drug only when the patient is cured (risk-sharing contract). The optimal contract depends on the trade-off between the monitoring costs, the marginal production cost and the utility derived from treatment. A non-risk-sharing agreement will be preferred by the health authority, if patients who should not be treated impose a relatively low cost to the health system. When this cost is high, the health authority would prefer a risk-sharing agreement for relatively low monitoring costs.
Experimental characterization of dielectric properties of carbon nanotube networks
Authors: EL Sabbagh Mahmoud A.
Published: February 2011

This paper explores the characterization of dielectric and conductive properties of carbon nanotube (CNT) networks. This is carried out by building planar transmission lines where conventional metallic traces are replaced by CNT networks. The proposed transmission lines with CNT networks are presented. Experimental realization and repeated two-port microwave measurements of proposed transmission lines enable the accurate extractions of their fundamental parameters showing percolation effects due to presence of CNT networks. The frequency-dependent phase velocity characteristics show a dramatic reduction compared to the speed of light in vacuum. The large magnitude of extracted complex permittivity for CNT networks also exhibits its percolation performance. The effects of CNTs' bulk density on measured and calculated parameters are explained. The results presented in this paper demonstrate the feasibility and the potential of building transmission lines and radio-frequency (RF) circuits elements using CNT networks.
A critical role for IL‐15 in TLR‐mediated innate antiviral immunity against genital HSV‐2 infection
Authors: Thatte Amit , DeWitte‐Orr Stephanie J , Lichty Brian , Mossman Karen L , Ashkar Ali A
Published: February 2011

Innate antiviral immunity, particularly at mucosal surfaces, has a critical role in early control of viral infections. Both type I interferons (IFNs) and interleukin‐15 (IL‐15) are essential components of innate antiviral immunity. It has been shown that toll‐like receptor (TLR) ligand‐induced innate antiviral immunity requires IFN‐α/β and ‐λ receptor signaling. However, it is not known if IL‐15 has a role in TLR ligand‐mediated antiviral responses. Here, we report that ligands for TLR‐3 and TLR‐9 cannot confer protection against genital herpes simplex virus‐2 (HSV‐2) in the absence of IL‐15 in vivo. Interestingly, wild‐type mice depleted of natural killer (NK) cells and treated with TLR ligands are protected upon HSV‐2 challenge, suggesting that the critical role of IL‐15 is independent of NK cell‐mediated activity. To examine the cytokine response in the absence of IL‐15, we investigated TLR ligand‐induced IFN‐β and ‐λ production in the vaginal washes, but found no impairment in IL‐15−/− mice. Finally, we report no impairment in the expression of the IFN‐stimulated genes in IL‐15−/− mice. Collectively, the data suggest that TLR ligands induce an IFN‐mediated response in the vaginal tract of both wild‐type and IL‐15−/− mice, but its induction is insufficient for providing protection against HSV‐2 in the absence of IL‐15.
Disinhibited Eating in Obese Adolescents Is Associated With Orbitofrontal Volume Reductions and Executive Dysfunction
Authors: Maayan Lawrence , Hoogendoorn Claire , Sweat Victoria , Convit Antonio
Published: February 2011

In adults, obesity has been associated with disinhibited eating, decreased cortical gray matter (GM) volume, and lower performance on cognitive assessments. Much less is known about these relationships in adolescence and there are no studies assessing behavioral, cognitive, and neurostructural measures in the same group of study participants. This study examined the relationship between obesity, executive function, disinhibition, and brain volumes in relatively healthy youth. Participants included 54 obese and 37 lean adolescents. Participants received a cognitive battery, questionnaires of eating behaviors, and magnetic resonance imaging (MRI). Neuropsychological assessments included tasks targeting frontal lobe function. Eating behaviors were determined using the Three Factor Eating Questionnaire (TFEQ), and structural MRIs were performed on a 1.5 T Siemens Avanto MRI System (Siemens, Erlangen, Germany) to determine brain GM volumes. Lean and obese adolescents were matched on age, years of education, gender, and socioeconomic status. Relative to lean adolescents, obese participants had significantly higher ratings of disinhibition on the TFEQ, lower performance on the cognitive tests, and lower orbitofrontal cortex (OFC) volume. Disinhibition significantly correlated with BMI, Stroop color‐word score, and OFC volume. This is the first report of these associations in adolescents and point to the importance of better understanding the associations between neurostructural deficits and obesity.
Preferences Predict Food Intake From 5 to 11 Years, but Not in Girls With Higher Weight Concerns, Dietary Restraint, and %Body Fat
Authors: Rollins Brandi Y. , Loken Eric , Birch Leann L.
Published: February 2011

Food preferences (FP) predict food intake in childhood; however, the predictive power of FP may decline among girls as weight concerns (WC) and dietary restraint (DR) increase during preadolescence. To examine longitudinal change in the preference‐intake (P‐I) relation and assess whether this relation weakens among non‐Hispanic white girls (n = 197) with a history of WC and DR from age 5 to 11. Girls' preferences for and intake (kcal) of 10 palatable snack foods were assessed biennially. Height, weight, percent body fat (%BF), WC, and DR were measured. Individual correlation coefficients were calculated per girl to capture within‐person P‐I correlations at each time of measurement. Overall, FP predicted girls' snack food calorie intakes between 5 and 11 years, but latent profile analysis (LPA) revealed three distinct patterns of change in P‐I correlations over time: “strong/stable” P‐I correlations were relatively high and became stronger with age; “increasing/later null” P‐I correlations were initially weak and became stronger between 5 and 9 years, but dropped to near 0 at 11 years; “initially weak/later strong” P‐I correlations were initially null and increased with age. Mixed models revealed that the “increasing/later null” group had greater increases in %BF, and higher WC, DR, and BMI percentiles from 5 to 11 years, compared to the other groups. In summary, FP predicted snack food calorie intake among most girls during childhood, but waned as a predictor of calorie intake at age 11 for a subset of girls with increasing %BF, and higher WC, DR, and BMIs.
High Prevalence of Prolonged QT Interval in Obese Hypogonadal Males
Authors: Pecori‐Giraldi Francesca , Manzoni Giuseppina , Michailidis Jorgo , Scacchi Massimo , Stramba‐Badiale Marco , Cavagnini Francesco
Published: February 2011

Obese subjects show several electrocardiographic alterations, including prolonged QT interval, a marker for fatal cardiac arrhythmias. Prolonged QT interval has recently been linked to low testosterone levels, a frequent occurrence in male obese patients but no study has yet assessed whether hypoandrogenism contributes to QT interval prolongation in this population. Aim of this study was to evaluate whether prolonged QT interval is linked to hypogonadism in male obese subjects. QT interval corrected for heart rate (QTc) was measured from standard electrocardiogram recordings in 136 obese men (BMI 30 >kg/m2, range 30.1–75.4 kg/m2). Obese men were classified as eugonadal or hypogonadal according to serum total testosterone levels (i.e., greater or less than 9.9 nmol/l). Our study showed that QTc measurements corrected by either Bazett (419 ± 3.2 vs. 408 ± 3.4 ms, P < 0.05), Fridericia (406.3 ± 3.39 vs. 396.4 ± 3.03 ms, P < 0.05) or Hodges (407.0 ± 3.12 vs. 397.3 ± 2.84 ms, P < 0.05) were longer in hypogonadal compared with eugonadal obese men; further, prolonged QTc interval (i.e., >440 ms) was more frequent among hypogonadal compared with eugonadal obese men (23% vs. 10%, P < 0.05). The degree of weight excess, diabetes, sleep apnoea and potassium levels were not associated with prolonged QTc. In conclusion, obese hypogonadal men show a greater prevalence of prolonged QT interval compared with their eugonadal counterparts. It appears therefore that low levels of testosterone in obese men may contribute to the arrhythmogenic profile of these patients, a heretofore unknown link which warrants further clinical attention.
Involvement of the PLCε/PKCα pathway in human BIU‐87 bladder cancer cell proliferation
Authors: Ling Yan , Chunli Luo , Xiaohou Wu , Qiaoling Zhang
Published: February 2011

PLCε (phospholipase Cε), one of effectors belonging to the small GTPase superfamily, has been suggested to play a crucial role in carcinogenesis. However, its bio‐function in bladder cancer has never been demonstrated. In our previous study, we found that PLCε mRNA was highly expressed in bladder cancer tissues. In the present study, we silenced the PLCε gene by shRNA (small‐hairpin RNA) in the bladder cancer cell line BIU‐87. The results showed that it significantly inhibited cell proliferation and arrested the cell cycle at G0/G1‐phase. The regulation of cell characteristics has been related to PKCα (protein kinase Cα) activity. Further study showed that knockdown of the PLCε gene down‐regulated oncogenes c‐fos and c‐jun. These results indicate that PLCε plays a crucial role in bladder cancer, and PLCε may be a key molecule regulating the signal pathway of bladder cancer proliferation.
Water formation by surface O3 hydrogenation
Authors: Romanzin C. , Ioppolo S. , Cuppen H. M. , van Dishoeck E. F. , Linnartz H.
Published: February 2011

Three solid state formation routes have been proposed in the past to explain the observed abundance of water in space: the hydrogenation reaction channels of atomic oxygen (O + H), molecular oxygen (O2 + H), and ozone (O3 + H). New data are presented here for the third scheme with a focus on the reactions O3 + H, OH + H and OH + H2, which were difficult to quantify in previous studies. A comprehensive set of H/D-atom addition experiments is presented for astronomically relevant temperatures. Starting from the hydrogenation/deuteration of solid O3 ice, we find experimental evidence for H2O/D2O (and H2O2/D2O2) ice formation using reflection absorption infrared spectroscopy. The temperature and H/D-atom flux dependence are studied and this provides information on the mobility of ozone within the ice and possible isotope effects in the reaction scheme. The experiments show that the O3 + H channel takes place through stages that interact with the O and O2 hydrogenation reaction schemes. It is also found that the reaction OH + H2 (OH + H), as an intermediate step, plays a prominent (less efficient) role. The main conclusion is that solid O3 hydrogenation offers a potential reaction channel for the formation of water in space. Moreover, the nondetection of solid ozone in dense molecular clouds is consistent with the astrophysical picture in which O3 + H is an efficient process under interstellar conditions.
Registration of Alfvén resonances in TCABR tokamak by the scanning reflectometer at sideband frequencies
Authors: Ruchko L. F. , Elfimov A. G. , Teixeira C. M. , Elizondo J. I. , Sanada E. , Galvão R. M. O. , Manso M. E. , Silva A.
Published: February 2011

A frequency scanning O-mode reflectometer was used for studies of plasma density oscillations during local Alfvén wave (LAW) excitation in the Tokamak Chauffage Alfvén Brésilien (TCABR) at the frequency fA = 5 MHz. It was found that the spectrum of the reflectometer output signal, which consists mainly of the “beat” frequency fB, is modified by the LAW excitation, and two additional frequency peaks appear, which are symmetrical in relation to the LAW excitation frequency f = fA ± fB. This result opens the possibility to improve the efficiency of studying the LAW induced density oscillations. The symmetry of these frequency peaks yields the possibility of finding the microwave frequency at which the reflectometer cutoff layer coincides with radial position of the LAW resonance zone in the TCABR tokamak.
Spectroscopic evidence of the formation of (V,Ti)O2 solid solution in VO2 thinner films grown on TiO2(001) substrates
Authors: Muraoka Y. , Saeki K. , Eguchi R. , Wakita T. , Hirai M. , Yokoya T. , Shin S.
Published: February 2011

We have prepared VO2 thin films epitaxially grown on TiO2(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO2 itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO2 substrates, with a chemical state similar to that in (V,Ti)O2 solid solution. These results indicate that insulating (V,Ti)O2 solid solution is formed in the thinner films. We propose a simple growth model of a VO2 thin film on a TiO2(001) substrate. Near the interface, insulating (V,Ti)O2 solid solution is formed due to the diffusion of Ti ions from the TiO2 substrate into the VO2 film. The concentration of Ti in (V,Ti)O2 is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO2 thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO2 thin films and TiO2 substrates is a key issue to study the physical property of an ultrathin film of “pure” VO2, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations.
Structural, mechanical, and thermodynamic properties of a coarse-grained DNA model
Authors: Ouldridge Thomas E. , Louis Ard A. , Doye Jonathan P. K.
Published: February 2011

We explore in detail the structural, mechanical, and thermodynamic properties of a coarse-grained model of DNA similar to that recently introduced in a study of DNA nanotweezers [T. E. Ouldridge, A. A. Louis, and J. P. K. Doye, Phys. Rev. Lett. 134, 178101 (2010)]. Effective interactions are used to represent chain connectivity, excluded volume, base stacking, and hydrogen bonding, naturally reproducing a range of DNA behavior. The model incorporates the specificity of Watson–Crick base pairing, but otherwise neglects sequence dependence of interaction strengths, resulting in an “average base” description of DNA. We quantify the relation to experiment of the thermodynamics of single-stranded stacking, duplex hybridization, and hairpin formation, as well as structural properties such as the persistence length of single strands and duplexes, and the elastic torsional and stretching moduli of double helices. We also explore the model's representation of more complex motifs involving dangling ends, bulged bases and internal loops, and the effect of stacking and fraying on the thermodynamics of the duplex formation transition.
Disposable parallel poly(dimethylsiloxane) microbioreactor with integrated readout grid for germination screening of Aspergillus ochraceus
Authors: Demming S. , Sommer B. , Llobera A. , Rasch D. , Krull R. , Büttgenbach S.
Published: February 2011

In this work a disposable, parallel microbioreactor (MBR) suitable for screening in batch or continuous mode is presented. The reactor consists of five parallel microchambers made of poly(dimethylsiloxane) bonded to a glass substrate. A grid structure is engraved on each chamber, allowing subsequent morphology imaging. Measurements are recorded over the entire cultivation period with constant parameters, namely, position and focus in the z-axis. The microdevice may be used for either parallel, uni- or multiparametric screening, and overcomes the drawback of gridless microwell plates which require expensive equipment such as an inverted microscope with an automatic stage. To validate the scalability from laboratory scale to microscale, and thus the cultivation protocol in the MBR, the germination of fungal spores (A. ochraceus) is evaluated for two different key magnitudes (pH and temperature) and compared to the results obtained from conventional laboratory scale systems (flasks and agar plates). Information on germination capacity with regard to interspecies’ variability allows for optimization of industrial processes as optimal pH and temperature matched to the mesoscopic cultivation systems. The germination conditions therefore remain unaffected inside the MBR, while providing the following advantages: (i) dramatic reduction of medium consumption, (ii) submerged cultivation with constant oxygen supply, (iii) assured low cost and disposability, and (iv) possibility of a continuous cultivation mode.
A two-dimensional polarization interferometry based parallel scan angular surface plasmon resonance biosensor
Authors: Liu Le , Ma Suihua , Ji Yanhong , Chong Xinyuan , Liu Zhiyi , He Yonghong , Guo Jihua
Published: February 2011

We describe a two-dimensional polarization interferometry based parallel scan angular surface plasmon resonance (SPR) biosensing technique. The method of line-shaped light illumination and parallel scan offers a high throughput. The simultaneous record of SPR angular spectrum enables the system to be unaffected by the time-dependent variation of the light source. The polarization interferometry technique lowers the minimum of the SPR dip and thereby reduces the noise related to the light intensity. Refractive index resolutions of 1.4 × 10−6 refractive index unit (RIU) under normal condition and 4.6 × 10−7 RIU under a more time-consuming condition are achieved in our angle interrogation based sensor. Meanwhile, a manually prepared DNA microarray has been detected, showing the potential applications of this technique in microarray analysis.
Enhancement of electric double layer capacitance of carbon nanotubes by gallium ion irradiation
Authors: Rai Padmnabh , Pandey Srikrishna , Menemparabath Minimol , Sug Kim Young , Ha Lee Il , Nikolaev Pavel , Arepalli Sivaram
Published: February 2011

Irradiation by 30 keV Ga+ ions was used to create defects in multiwalled carbon nanotubes. Damage to the graphitic structure of the nanotube wall resulting from ion irradiation was observed by a transmission electron microscope which was accompanied by corresponding changes in Raman spectra. It was found that ion irradiation at 2 × 1013 ions/cm2 cumulative dose increases the electric double layer capacitance of a multiwalled carbon nanotube electrode by a factor of 2.3, followed by a decrease and saturation at higher (2 × 1014 and 4 × 1014 ions/cm2) doses. This might be a trade-off between the enhancement caused by the tip opening and lowering of the capacitance due to amorphization of carbon nanotubes.
X-ray Raman compression via two-stream instability in dense plasmas
Authors: Son S. , Moon Sung Joon
Published: February 2011

A Raman compression scheme suitable for x-rays, where the Langmuir wave is created by an intense beam rather than the ponderomotive potential between the seed and pump pulses, is proposed. The required intensity of the seed and pump pulses enabling the compression could be mitigated by more than a factor of 100 compared to conventionally available other Raman compression schemes. The relevant wavelength of x-rays ranges from 1 to 10 nm.
Vibrational spectrum of Ar3+ and relative importance of linear and perpendicular isomers in its photodissociation
Authors: Karlický František , Lepetit Bruno , Kalus René , Gadéa Florent Xavier
Published: February 2011

The photodissociation dynamics of the argon ionized trimer \documentclass[12pt]{minimal}\begin{document}${\rm Ar}_3^+$\end{document} Ar 3+ is revisited in the light of recent experimental results of Lepère et al. [J. Chem. Phys. 134, 194301 (2009)], which show that the fragment with little kinetic energy is always a neutral one, thus the available energy is shared by a neutral and ionic fragments as in \documentclass[12pt]{minimal}\begin{document}${\rm Ar}_2^+$\end{document} Ar 2+. We show that these results can be interpreted as the photodissociation of the linear isomer of the system. We perform a 3D quantum computation of the vibrational spectrum of the system and study the relative populations of the linear (trimer-core) and perpendicular (dimer-core) isomers. We then show that the charge initially located on the central atom in the ground electronic state of the linear isomer migrates toward the extreme ones in the photoexcitation process such that photodissociation of the linear isomer produces a neutral central atom at rest in agreement with measured product state distributions.
Multiferroicity in an orthorhombic YMnO3 single-crystal film
Authors: Nakamura Masao , Tokunaga Yusuke , Kawasaki Masashi , Tokura Yoshinori
Published: February 2011

Perovskitelike RMnO3 (R: rare-earth) exhibits large magnetoelectric effects because of the intimate correlation between magnetic and ferroelectric orders. However, reproducing the multiferroic properties in thin films has been far from straightforward due to the difficulty in the growth of single-crystal films caused by the large orthorhombic distortion in RMnO3. We could overcome the problem and achieve the fabrication of a monodomain single-crystal film of orthorhombic YMnO3 by choosing (0 1 0)-YAlO3 as a substrate. The film showed a ferroelectric transition at 40 K with a saturation polarization of 0.8 μC/cm2. The ferroelectric polarization could be modified by magnetic fields, evidencing the multiferroic state in the film.
Defects in ZnO transparent conductors studied by capacitance transients at ZnO/Si interface
Authors: Li Baoe , Adachi Yutaka , Li Jianyong , Okushi Hedeyo , Sakaguchi Isao , Ueda Shigenori , Yoshikawa Hideki , Yamashita Yoshiyuki , Senju Shoichi , Kobayashi Keisuke , Sumiya Masatomo , Haneda Hajime , Ohashi Naoki
Published: February 2011

Deep levels in heavily aluminum-doped zinc oxide (AZO) thin film were studied by transient capacitance (C-t) measurements and photoemission spectroscopy (PES). To study degenerated AZO by C-t measurements, AZO films were deposited on a p-type silicon (p-Si) substrate to form a depletion layer at the AZO/p-Si interface. Analyses of C-t behavior revealed that concentration of a trap level 0.3 eV below the bottom of the conduction was on the order of 1019 cm−3, which is 20%–50% of the shallow donor concentration. Such a high concentration of the trap level in AZO was evidenced by subsequent PES measurements.
Magnitude and sign control of lithography-induced uniaxial anisotropy in ultra-thin (Ga,Mn)As wires
Authors: Shiogai J. , Schuh D. , Wegscheider W. , Kohda M. , Nitta J. , Weiss D.
Published: February 2011

We were able to control the magnitude and sign of the uniaxial anisotropy in 5-nm-thin (Ga,Mn)As wires by changing the crystallographic direction of the lithography-induced strain relaxation. The 1-μm-wide (Ga,Mn)As wires, oriented in [110] and [11¯0] directions, were fabricated using electron beam lithography. Their magnetic anisotropies were studied by a coherent rotation method at temperatures between 4.5 and 75 K. Depending on the orientation of the wire, the additional uniaxial anisotropy observed along the axis of the 1-μm-wide samples either increased or decreased the total uniaxial anisotropy.
On the kinetics of platinum silicide formation
Authors: Faber Erik J. , Wolters Rob A. M. , Schmitz Jurriaan
Published: February 2011

In this work, the kinetics of platinum silicide formation for thin Pt films (50 nm) on monocrystalline ⟨100⟩ silicon is investigated via in situ resistance measurements under isothermal (197–275 °C) conditions. For Pt2Si diffusion limited growth was observed. For PtSi formation, however, no linear relation between silicide thickness and √t was found. PtSi growth over time could be described using the Avrami relation rendering Avrami exponent n=1.4±0.1. Additionally, an effective activation energy EA=1.7±0.1 eV was derived using the Avrami k values. The findings are important for obtaining well defined silicide films and silicide-to-silicon contacts.
Possible routes for synthesis of new boron-rich Fe–B and Fe1−xCrxB4 compounds
Authors: Bialon A. F. , Hammerschmidt T. , Drautz R. , Shah S. , Margine E. R. , Kolmogorov A. N.
Published: February 2011

We use ab initio calculations to examine thermodynamic factors that could promote the formation of recently proposed unique oP10-FeB4 and oP12-FeB2 compounds. We demonstrate that these compact boron-rich phases are stabilized further under pressure. We also show that chromium tetraboride is more stable in the new oP10 rather than the reported oI10 structure which opens up the possibility of realizing an oP10-(FexCr1−x)B4 pseudobinary material. In addition to exhibiting remarkable electronic features, oP10-FeB4 and oP12-FeB2 are expected to be harder than the known Fe–B compounds commonly used for hard coating applications.
Radiative defects in GaN nanocolumns: Correlation with growth conditions and sample morphology
Authors: Lefebvre P. , Fernández-Garrido S. , Grandal J. , Ristić J. , Sánchez-García M.-A. , Calleja E.
Published: February 2011

Low-temperature photoluminescence is studied in detail in GaN nanocolumns (NCs) grown by plasma-assisted molecular beam epitaxy under various conditions (substrate temperature and impinging Ga/N flux ratio). The relative intensities of the different emission lines, in particular those related to structural defects, appear to be correlated with the growth conditions, and clearly linked to the NC sample morphology. We demonstrate, in particular, that all lines comprised between 3.10 and 3.42 eV rapidly lose intensity when the growth conditions are such that the NC coalescence is reduced. The well-known line around 3.45 eV, characteristic of GaN NC samples, shows, however, a behavior that is exactly the opposite of the other lines, namely, for growth conditions leading to reduced NC coalescence, this line tends to become more prominent, thus proving to be intrinsic to individual GaN NCs.
Tuning lattice thermal conductance by porosity control in ultrascaled Si and Ge nanowires
Authors: Paul Abhijeet , Klimeck Gerhard
Published: February 2011

Porous nanowires (NWs) with tunable thermal conductance are examined as a candidate for thermoelectric devices with high efficiency. Thermal conductance (σl) of porous NWs is calculated using the phonon dispersion obtained from a modified valence force field model. Porosity in the NWs break the crystal symmetry leading to the reduction in ballistic σl. [100] Si and Ge NWs show similar percentage reductions in σl for the same amount of porosity. The model predicts an anisotropic reduction in σl in SiNWs, with [111] showing the maximum reduction followed by [100] and [110] for a similar hole radius. The reduction in σl is attributed to phonon localization and anisotropic mode reduction.
Photonic properties of erbium doped InGaN alloys grown on Si (001) substrates
Authors: Feng I. W. , Cao X. K. , Li J. , Lin J. Y. , Jiang H. X. , Sawaki N. , Honda Y. , Tanikawa T. , Zavada J. M.
Published: February 2011

Erbium doped InGaN alloys (InGaN:Er) were grown on Si (001) substrates using metal organic chemical vapor deposition. The growth of epitaxial films was accomplished by depositing InGaN:Er on GaN templates deposited on 7.3° off-oriented Si (001) substrates which were prepared by etching and subsequent selective area growth. X-ray diffraction measurements confirmed the formation of wurtzite InGaN (11¯01) epilayers, which exhibit strong photoluminescence emission at 1.54 μm. The observed emission intensity at 1.54 μm was comparable to that from similar alloys grown on GaN/AlN/Al2O3 templates. These results indicate the high potential for on-chip integration of erbium based photonic devices with complementary metal oxide semiconductor technology.
Modeling the nanoscratching of self-healing materials
Authors: Duki Solomon F. , Kolmakov German V. , Yashin Victor V. , Kowalewski Tomasz , Matyjaszewski Krzysztof , Balazs Anna C.
Published: February 2011

We use computational modeling to determine the mechanical response of crosslinked nanogels to an atomic force microscope (AFM) tip that is moved through the sample. We focus on two-dimensional systems where the nanogels are interconnected by both strong and labile bonds. To simulate this system, we modify the lattice spring model (LSM) to extend the applicability of this method to a broader range of elastic materials. Via this modified LSM, we model each nanogel as a deformable particle. We utilize the Bell model to describe the bonds between these nanogel particles, and subsequently, simulate the rupturing of bonds due to the force exerted by the moving indenter. The ruptured labile bonds can readily reform and thus can effectively mend the cavities formed by the moving AFM tip. We determine how the fraction of labile bonds, the nanogel stiffness, and the size and velocity of the moving tip affect the self-healing behavior of the material. We find that samples containing just 10% of labile bonds can heal to approximately 90% of their original, undeformed morphology. Our results provide guidelines for creating reconfigurable materials that can undergo self-repair and thereby withstand greater mechanical stress under everyday use.
Hydrogenation of magnesium nanoblades: The effect of concentration dependent hydrogen diffusion
Authors: Yang B. , He Y.-P. , Zhao Y.-P.
Published: February 2011

By assuming the H diffusion coefficient and H adsorption rate to be exponentially and linearly dependent on concentration, a physical model is developed to predict the hydrogenation process of Mg nanoblades. The predicted H uptake curves agree well with the experimental data from V-coated Mg nanoblades. The obtained H diffusion coefficients in MgHx between Mg and MgH2 have nearly three orders of magnitude variation. The characteristic time of H surface adsorption is longer than that of H diffusion in Mg but shorter than that in MgH2 for 100 nm thick nanoblades. A hydride shell is not formed during the hydrogenation.
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-like hybridization of silicon valence orbitals in silicene nanoribbons
Authors: De Padova Paola , Quaresima Claudio , Olivieri Bruno , Perfetti Paolo , Le Lay Guy
Published: February 2011

Silicene nanoribbons grown on a silver (110) substrate have been studied by reflection electron energy loss spectroscopy as a function of the electron beam incidence angle α. The spectra, taken at the Si K absorption edge (1.840 keV), reveal the presence of two distinct loss structures attributed to transitions 1s→π∗ and 1s→σ∗, according to their intensity dependence on α. Such behavior, when compared to graphite, attests the sp2-like hybridization of the silicon valence orbitals in the silicene nanoribbons as is, indeed, for carbon atomic bonds of graphene.
Strong exciton-photon coupling with colloidal quantum dots in a high-Q bilayer microcavity
Authors: Giebink Noel C. , Wiederrecht Gary P. , Wasielewski Michael R.
Published: February 2011

We demonstrate evanescently coupled bilayer microcavities with Q-factors exceeding 250 fabricated by a simple spin-coating process. The cavity architecture consists of a slab waveguide lying upon a low refractive index spacer layer supported by a glass substrate. For a lossless guide layer, the cavity Q depends only on the thickness of the low index spacer and in principle can reach arbitrarily high values. We demonstrate the versatility of this approach by constructing cavities with a guide layer incorporating CdSe/ZnS core/shell quantum dots, where we observe strong coupling and hybridization between the 1S(e)-1S3/2(h) and 1S(e)-2S3/2(h) exciton states mediated by the cavity photon. This technique greatly simplifies the fabrication of high-Q planar microcavities for organic and inorganic quantum dot thin films and opens up new opportunities for the study of nonlinear optical phenomena in these materials.
Hypoxia and lineage specification of cell line-derived colorectal cancer stem cells
Authors: Yeung Trevor M. , Gandhi Shaan C. , Bodmer Walter F.
Published: February 2011

Hypoxia is an important regulator of normal and cancer stem cell (CSC) differentiation. Colorectal CSCs from SW1222, LS180, and CCK81 colorectal cancer-derived cell lines are able to differentiate into complex 3D lumen-containing structures in normoxia, whereas in hypoxia, they form undifferentiated dense colonies that have reduced expression of the enterocyte differentiation marker CDX1, lack goblet cell formation, and have increased expression of BMI1 and activated Notch1. Hypoxia increases the clonogenicity of CSCs, which is cumulative as each round of hypoxia enriches for more CSCs. The hypoxic phenotype is reversible, because cells from hypoxic-dense colonies are able to reform differentiated structures when regrown in normoxia. We show that CDX1 is able to stimulate the generation of lumens even in hypoxia and has a negative feedback on BMI1 expression. Knockdown of CDX1 reduces lumen formation but does not affect goblet cell formation, suggesting that enterocytes and goblet cells form from different progenitor cells. Notch inhibition by dibenzazepine (DBZ) allowed CSCs to form goblet cells in both normoxia and hypoxia. Finally, we show that Hif1α, but not CA9, is an important mediator of the effects of hypoxia on the clonogenicity and differentiation of CSCs. In summary, hypoxia maintains the stem-like phenotype of colorectal cell line-derived CSCs and prevents differentiation of enterocytes and goblet cells by regulating CDX1 and Notch1, suggesting that this regulation is an important component of how hypoxia controls the switch between stemness and differentiation in CSCs.
The Khwushnishin Population of Iran
Authors: Hooglund Eric J.
Published: February 2011

Iranian villages generally contain two distinct social classes: (1) peasants who cultivate land they own and/or rent, and (2) landless non-farmers who engage in various commercial, service, and labor activities appropriate to an agricultural economy. Peasants generally employ one term to designate all landless villagers; the most widely used is “khwushnishin.” Although for peasants this term is useful, it poses some difficulty for the social scientist since khwushnishins do not comprise a homogeneous class, but rather are a collectivity of diverse occupational groups sharing in common only a landless status. Included among the khwushnishins are some of the wealthiest, as well as some of the poorest, of all villagers. In terms of economic and social stratification, one can identify at least three separate groups of khwushnishins. In this paper I propose to describe these three groups and analyze their unique roles in the villages.
Glypican-5 stimulates rhabdomyosarcoma cell proliferation by activating Hedgehog signaling
Authors: Li Fuchuan , Shi Wen , Capurro Mariana , Filmus Jorge
Published: February 2011

Glypican-5 (GPC5) is one of the six members of the glypican family. It has been previously reported that GPC5 stimulates the proliferation of rhabdomyosarcoma cells. In this study, we show that this stimulatory activity of GPC5 is a result of its ability to promote Hedgehog (Hh) signaling. We have previously shown that GPC3, another member of the glypican family, inhibits Hh signaling by competing with Patched 1 (Ptc1) for Hh binding. Furthermore, we showed that GPC3 binds to Hh through its core protein but not to Ptc1. In this paper, we demonstrate that GPC5 increases the binding of Sonic Hh to Ptc1. We also show that GPC5 binds to both Hh and Ptc1 through its glycosaminoglycan chains and that, unlike GPC3, GPC5 localizes to the primary cilia. Interestingly, we found that the heparan sulfate chains of GPC5 display a significantly higher degree of sulfation than those of GPC3. Based on these results, we propose that GPC5 stimulates Hh signaling by facilitating/stabilizing the interaction between Hh and Ptc1.
The autophagy protein Atg7 is essential for hematopoietic stem cell maintenance
Authors: Mortensen Monika , Soilleux Elizabeth J. , Djordjevic Gordana , Tripp Rebecca , Lutteropp Michael , Sadighi-Akha Elham , Stranks Amanda J. , Glanville Julie , Knight Samantha , W. Jacobsen Sten-Eirik , Kranc Kamil R. , Simon Anna Katharina
Published: February 2011

The role of autophagy, a lysosomal degradation pathway which prevents cellular damage, in the maintenance of adult mouse hematopoietic stem cells (HSCs) remains unknown. Although normal HSCs sustain life-long hematopoiesis, malignant transformation of HSCs leads to leukemia. Therefore, mechanisms protecting HSCs from cellular damage are essential to prevent hematopoietic malignancies. In this study, we crippled autophagy in HSCs by conditionally deleting the essential autophagy gene Atg7 in the hematopoietic system. This resulted in the loss of normal HSC functions, a severe myeloproliferation, and death of the mice within weeks. The hematopoietic stem and progenitor cell compartment displayed an accumulation of mitochondria and reactive oxygen species, as well as increased proliferation and DNA damage. HSCs within the Lin−Sca-1+c-Kit+ (LSK) compartment were significantly reduced. Although the overall LSK compartment was expanded, Atg7-deficient LSK cells failed to reconstitute the hematopoietic system of lethally irradiated mice. Consistent with loss of HSC functions, the production of both lymphoid and myeloid progenitors was impaired in the absence of Atg7. Collectively, these data show that Atg7 is an essential regulator of adult HSC maintenance.
Cutaneous immunosurveillance by self-renewing dermal γδ T cells
Authors: Sumaria Nital , Roediger Ben , Ng Lai Guan , Qin Jim , Pinto Rachel , Cavanagh Lois L. , Shklovskaya Elena , Fazekas de St. Groth Barbara , Triccas James A. , Weninger Wolfgang
Published: February 2011

The presence of γδ T cell receptor (TCR)–expressing cells in the epidermis of mice, termed dendritic epidermal T cells (DETCs), is well established. Because of their strict epidermal localization, it is likely that DETCs primarily respond to epithelial stress, such as infections or the presence of transformed cells, whereas they may not participate directly in dermal immune responses. In this study, we describe a prominent population of resident dermal γδ T cells, which differ from DETCs in TCR usage, phenotype, and migratory behavior. Dermal γδ T cells are radioresistant, cycle in situ, and are partially depend on interleukin (IL)-7, but not IL-15, for their development and survival. During mycobacterial infection, dermal γδ T cells are the predominant dermal cells that produce IL-17. Absence of dermal γδ T cells is associated with decreased expansion in skin draining lymph nodes of CD4+ T cells specific for an immunodominant Mycobacterium tuberculosis epitope. Decreased CD4+ T cell expansion is related to a reduction in neutrophil recruitment to the skin and decreased BCG shuttling to draining lymph nodes. Thus, dermal γδ T cells are an important part of the resident cutaneous immunosurveillance program. Our data demonstrate functional specialization of T cells in distinct microcompartments of the skin.
Eph-B4 prevents venous adaptive remodeling in the adult arterial environment
Authors: Muto Akihito , Yi Tai , Harrison Kenneth D. , Dávalos Alberto , Fancher Tiffany T. , Ziegler Kenneth R. , Feigel Amanda , Kondo Yuka , Nishibe Toshiya , Sessa William C. , Dardik Alan
Published: February 2011

Eph-B4 determines mammalian venous differentiation in the embryo but is thought to be a quiescent marker of adult veins. We have previously shown that surgical transposition of a vein into the arterial environment is characterized by loss of venous identity, as indicated by the loss of Eph-B4, and intimal thickening. We used a mouse model of vein graft implantation to test the hypothesis that Eph-B4 is a critical determinant of venous wall thickness during postsurgical adaptation to the arterial environment. We show that stimulation of Eph-B4 signaling, either via ligand stimulation or expression of a constitutively active Eph-B4, inhibits venous wall thickening and preserves venous identity; conversely, reduction of Eph-B4 signaling is associated with increased venous wall thickness. Stimulated Eph-B4 associates with caveolin-1 (Cav-1); loss of Cav-1 or Eph-B4 kinase function abolishes inhibition of vein graft thickening. These results show that Eph-B4 is active in adult veins and regulates venous remodeling. Eph-B4–Cav-1–mediated vessel remodeling may be a venous-specific adaptive mechanism. Controlled stimulation of embryonic signaling pathways such as Eph-B4 may be a novel strategy to manipulate venous wall remodeling in adults.
Thymic stromal lymphopoietin fosters human breast tumor growth by promoting type 2 inflammation
Authors: Pedroza-Gonzalez Alexander , Xu Kangling , Wu Te-Chia , Aspord Caroline , Tindle Sasha , Marches Florentina , Gallegos Michael , Burton Elizabeth C. , Savino Daniel , Hori Toshiyuki , Tanaka Yuetsu , Zurawski Sandra , Zurawski Gerard , Bover Laura , Liu Yong-Jun , Banchereau Jacques , Palucka A. Karolina
Published: February 2011

The human breast tumor microenvironment can display features of T helper type 2 (Th2) inflammation, and Th2 inflammation can promote tumor development. However, the molecular and cellular mechanisms contributing to Th2 inflammation in breast tumors remain unclear. Here, we show that human breast cancer cells produce thymic stromal lymphopoietin (TSLP). Breast tumor supernatants, in a TSLP-dependent manner, induce expression of OX40L on dendritic cells (DCs). OX40L+ DCs are found in primary breast tumor infiltrates. OX40L+ DCs drive development of inflammatory Th2 cells producing interleukin-13 and tumor necrosis factor in vitro. Antibodies neutralizing TSLP or OX40L inhibit breast tumor growth and interleukin-13 production in a xenograft model. Thus, breast cancer cell–derived TSLP contributes to the inflammatory Th2 microenvironment conducive to breast tumor development by inducing OX40L expression on DCs.