3,290 research outputs found
International Trade and Institutional Change
No full textThis paper analyzes the impact of international trade on the quality of institutions, such as contract enforcement, property rights, or investor protection. It presents a model in which institutional differences play two roles: they create rents for some parties within the economy, and they are a source of comparative advantage in trade. Institutional quality is determined in a Grossman-Helpman type lobbying game. When countries share the same technology, there is a race to the top" in institutional quality: irrespective of country characteristics, both trade partners are forced to improve institutions after opening. On the other hand, domestic institutions will not improve in either trading partner when one of the countries has a strong enough technological comparative advantage in the good that relies on institutions. We test these predictions in a sample of 141 countries, by extending the geography-based methodology of Frankel and Romer (1999). Countries whose exogenous geographical characteristics predispose them to exporting in institutionally intensive sectors enjoy significantly higher institutional quality.trade, institutional change
The Function of Themis2 in B Cells
No full textThymocyte-expressed molecule involved in selection 2 (Themis2) is the second member of the Themis family. Recently, the first member of the Themis family, Themis, has been reported to be part of the TCR signalling cascade and its deletion severely affects thymocyte progression from the double positive to the single positive stage. All family members share similar domains and high sequence similarity and show tissue specific expression with Themis2 being expressed in B lymphocytes, macrophages and dendritic cells. THEMIS2 associates with BCR signalling molecules such as GRB2, VAV or LYN and is phosphorylated in response to BCR stimulation. For these reasons I hypothesised that Themis2 might have an important role in B cell development or activation. I show that Themis2 is expressed throughout the B cell lineage and exclude redundant expression of other Themis family members. After B cell activation Themis2 expression is downregulated. Analysis of a newly created Themis2-deficient mouse strain showed that B cell development proceeds normally in the absence of THEMIS2. Experiments on in vitro cultured Themis2-deficient primary B cells demonstrated that proliferation and survival, BCR internalisation and antigen presentation as well as expression of activation markers and cytokines were unaffected. RNA sequencing revealed only minor changes in transcription in follicular B cells, even after activation. Similarly, antibody levels to in vivo immunisation with T-dependent or T-independent antigens or challenge with influenza virus did not suggest that Themis2 is required for antibody responses either. Reactions to a model of acute allergic airway inflammation showed only marginally reduced cell numbers in the bronchoalveolar lavage fluid yet all other markers of inflammation were all normal. In conclusion, I found that Themis2 is not required for B cell development, activation or antibody responses. Further studies will be required to define the role of Themis2 in the immune system
Back cover: Plasma Process. Polym. 8∕2014
No full text<b>Back Cover</b>\ud
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The growth mechanism was clarified and differences between the plasma- and neutral gas-grown carbon nanotubes were explained by using an enhanced large-scale model and numerical simulation technique. The nanotubes synthesized by plasma process can be longer than those synthesized by neutral gas technique. The low-temperature growth of the nanotube array is also possible when the hydrocarbon ion flux to the nanotubes dominates over fluxes of other species. Further details can be found in the article Gennady Burmaka et al. on page 798
Pros and Cons of (NH4)2S Solution Treatment of p-GaN/Metallization Interface: Perspectives for Laser Diode
No full textThe impact of wet treatment using an (NH4)2S-alcohol solution on the interface state of the p-GaN/Ni/Au/Pt contact system and laser diode processing was investigated. Sulfur wet cleaning resulted in reduced surface roughness and contact resistivity. The lowest specific contact resistance (ρc < 1 × 10−4 Ω·cm2) was achieved with samples treated with an (NH4)2S-isopropanol solution, whereas the highest resistivity (ρc = 3.3 × 10−4 Ω·cm2) and surface roughness (Ra = 16 nm) were observed in samples prepared by standard methods. Annealing the contact system in an N2 + O2 + H2O atmosphere caused degradation through species inter-diffusion and metal-metal solid solution formation, irrespective of the preparation method. Standard prepared substrates developed a thin GaN-Au intermediate layer at the interface after heat treatment. Enhanced adhesion and the absence of GaN decomposition were observed in samples additionally cleaned with the (NH4)2S-solvent solution. Complete oxidation of nickel to NiO was observed in samples that underwent additional sulfur solution treatment. The intensity of metal species mixing and nickel oxidation was influenced by the metal diffusion rate and was affected by the initial state of the GaN substrate obtained through different wet treatment methods.The names of files corespond to the numbering of the figures in the paper Iryna Levchenko,Serhii Kryvyi,Eliana Kamińska,Julita Smalc-Koziorowska,Szymon Grzanka,Jacek Kacperski,Grzegorz Nowak,Sławomir Kret,Łucja Marona and Piotr Perlin. Pros and Cons of (NH4)2S Solution Treatment of p-GaN/Metallization Interface: Perspectives for Laser Diode. https://doi.org/10.3390/ma17184520.Files include next collection:Figure 1. AFM overview scan of p-GaN surface after (a) standard cleaning and (b) standard and (NH4)2S-t-(CH3)3COH treatment.Figure 2. AFM maps (a–d) and SEM images (e–h) of the surface of annealed p-GaN/Ni/Au/Pt contact system.Figure 3. c-AFM current maps (a–d) and AFM images (e–h) of annealed p-GaN/Ni/Au/Pt.Figure 4. STEM image of annealed p-GaN/Ni/Au/Pt, after standard preparation (a) and with additional treatment by (NH4)2S solution (b).Figure 5. STEM image (a) and EDX maps of the element propagation (b–f) for the annealed p-GaN/Ni/Au/Pt system with treatment in (NH4)2S-based solution.Figure 6. Schematic view on evolution of the annealed p-GaN/Ni/Au/Pt system with treatment in (NH4)2S-based solution (grey circles represent the voids).Figure 7. STEM image (a) and EDX maps of the element dispersion (b–f) for the annealed p-GaN/Ni/Au/Pt system after standard cleaning.Figure 8. Schematic view on evolution of the annealed p-GaN/Ni/Au/Pt system after standard cleaning.</p
Palladium-Based Contacts on p-GaN and Their Application in Laser Diodes
No full textPalladium-Based Contacts on p-GaN and Their Application in Laser Diodes. Iryna Levchenko, Serhii Kryvyi, Eliana Kamińska, Szymon Grzanka, Ewa Grzanka, Łucja Marona and Piotr Perlin. Materials 2023, 16(19), 6568; https://doi.org/10.3390/ma16196568In this paper, we investigate the effect of Pd thickness and heat treatment on Pd/Ni/Au/p-GaN metal contacts. The as-deposited samples exhibit a smooth morphology and non-linear I–V characteristics. Heat treatment in a N2 atmosphere leads to degradation of the contact microstructure, resulting in diffusion of Ga, void formation on the interface and mixing of metals. Annealing in a mixture of N2 and O2 improves adhesion and reduces contact resistance. However, this process also induces GaN decomposition and species mixing. The mixing of metal–Ga and metal–metal remains unaffected by the method of thermal treatment but depends on gas composition for thin Pd contacts. To achieve low-resistance contacts (≈1 × 10−4 Ω cm2), we found that increasing the Pd thickness and using N2 + O2 as the annealing environment are effective measures. Nevertheless, the degradation effect of the annealed contact microstructure in the form of the void generation becomes evident as the thickness of Pd increases. Laser diodes (LDs) with optimized palladium-based contacts operate at a voltage of 4.1 V and a current density of 3.3 kA/cm².The names of files correspond to the nnumbering of the figures in the paper. It includes:Figure 1. SEM image of the surface of as-deposited Pd/Ni/Au (10/10/30 nm) metallization on p-GaN. The provided layer thicknesses correspond to the settings used for evaporation.Figure 2. XRD profile for investigated Pd/Ni/Au (10/10/30 nm) as-grown sample. The powder diffraction patterns with corresponding reference numbers in PDF-2 and ICSD databases are shown.Figure 3. HR-STEM image (a) of as-deposited Pd/Ni/Au (10/10/30 nm) together with the interplanar distance for the indicated lattice planes (b) determined from measurements by FFT. ZA—zone axis.Figure 4. Crystallographic orientation of GaN (a) and metal layers (b,c).Figure 5. I−V plots for the as-deposited and annealed contacts.Figure 6. SEM (a) and STEM (b) images of Pd/Ni/Au (10/10/30 nm) annealed in RTA in N2 flow at 530 °C.Figure 7. EDX elemental mapping data for p-GaN/Pd/Ni/Au (10/10/30 nm) contact annealed in N2 (a–f). Schematic view of the contact composition (g).Figure 8. XRD profiles for investigated as-grown sample and after annealing in N2.Figure 9. SEM data of Pd/Ni/Au (10/10/30 nm) annealed in RTA in N2 + O2 flow at 530 °C.Figure 10. EDX elemental mapping data (a–f) and schematic view (g) of Pd/Ni/Au (10/10/30 nm) annealed in RTA in N2 + O2 flow at 530 °C.Figure 11. XRD profiles for investigated as-grown sample after annealing by RTA in N2 + O2 flow.Figure 12. SEM data of Pd/Ni/Au (90/10/30 nm) after annealing by (a) oven in N2 + O2 + H2O and (b) RTA in N2 + O2.Figure 13. EDX maps of Pd/Ni/Au (90/10/30 nm) after annealing by oven in N2 + O2 + H2O (a–f) and scheme of Pd/Ni/Au (90/10/30 nm) composition (g).Figure 14. XRD profiles for investigated as-grown sample and after annealing.</p
Highly tunable electronic properties in plasma-synthesized B-doped microcrystalline-to-amorphous silicon nanostructure for solar cell applications
No full textHighly controllable electronic properties (carrier mobility and conductivity) were obtained in the sophisticatedly devised, structure-controlled, boron-doped microcrystalline silicon structure. Variation of plasma parameters enabled fabrication of films with the structure ranging from a highly crystalline (89.8%) to semi-amorphous (45.4%) phase. Application of the innovative process based on custom-designed, optimized, remote inductively coupled plasma implied all advantages of the plasma-driven technique and simultaneously avoided plasma-intrinsic disadvantages associated with ion bombardment and overheating. The high degree of SiH<sub>4</sub>, H<sub>2</sub> and B<sub>2</sub>H<sub>6</sub> precursor dissociation ensured very high boron incorporation into the structure, thus causing intense carrier scattering. Moreover, the microcrystalline-to-amorphous phase transition triggered by the heavy incorporation of the boron dopant with increasing B<sub>2</sub>H<sub>6</sub> flow was revealed, thus demonstrating a very high level of the structural control intrinsic to the process. Control over the electronic properties through variation of impurity incorporation enabled tailoring the carrier concentrations over two orders of magnitude (10<sup>18</sup>–10<sup>20</sup> cm<sup>−3</sup>). These results could contribute to boosting the properties of solar cells by paving the way to a cheap and efficient industry-oriented technique, guaranteeing a new application niche for this new generation of nanomaterials
Automation of Feynman diagram evaluation
No full textTentyukov M, Fleischer J. Automation of Feynman diagram evaluation. In: Sveshnikov NA, Levchenko BB, eds. Quantum field theory and high-energy physics. Proceedings. Workshop, QFTHEP'97, Samara, Russia, September 4-10, 1997. 4-10 September 1997. Samara, Russian Federation. Moskau: M.V.Lomonosova/Publishing House of Moscow State University; 1997: 318-321
Marginal Zone B Cells Regulate Antigen-Specific T Cell Responses during Infection
No full textMarginal zone B cells (MZB) participate in the early immune response to several pathogens. In this study, we show that in mu MT mice infected with Leishmania donovani, CD8 T cells displayed a greater cytotoxic potential and generated more effector memory cells compared with infected wild type mice. The frequency of parasite-specific, IFN-gamma(+) CD4 T cells was also increased in mu MT mice. B cells were able to capture parasites, which was associated with upregulation of surface IgM and MyD88-dependent IL-10 production. Moreover, MZB presented parasite Ags to CD4 T cells in vitro. Depletion of MZB also enhanced T cell responses and led to a decrease in the parasite burden but did not alter the generation of effector memory T cells. Thus, MZB appear to suppress protective T cell responses during the early stages of L. donovani infection.</br
Measurement of the t t ¯ H and tH production rates in the H → b b ¯ decay channel using proton-proton collision data at s = 13 TeV
No full textAbstract An analysis of the production of a Higgs boson (H) in association with a top quark-antiquark pair ( t t ¯ H ) or a single top quark (tH) is presented. The Higgs boson decay into a bottom quark-antiquark pair (H → b b ¯ ) is targeted, and three different final states of the top quark decays are considered, defined by the number of leptons (electrons or muons) in the event. The analysis utilises proton-proton collision data collected at the CERN LHC with the CMS experiment at s = 13 TeV in 2016–2018, which correspond to an integrated luminosity of 138 fb −1. The observed t t ¯ H production rate relative to the standard model expectation is 0.33 ± 0.26 = 0.33 ± 0.17(stat) ± 0.21(syst). Additionally, the t t ¯ H production rate is determined in intervals of Higgs boson transverse momentum. An upper limit at 95% confidence level is set on the tH production rate of 14.6 times the standard model prediction, with an expectation of 19.3 − 6.0 + 9.2 . Finally, constraints are derived on the strength and structure of the coupling between the Higgs boson and the top quark from simultaneous extraction of the t t ¯ H and tH production rates, and the results are combined with those obtained in other Higgs boson decay channels
Measurement of the ratio B(t -> Wb)/B(t -> Wq) in pp collisions at root s=8 TeV
No full textThe ratio of the top-quark branching fractions R = B(t --> Wb)/B(t --> Wq), where the denominator includes the sum over all down-type quarks (q = b, s, d), is measured in the t (t) over bar dilepton final state with proton-proton collision data at root s = 8 TeV from an integrated luminosity of 19.7 fb(-1), collected with the CMS detector. In order to quantify the purity of the signal sample, the cross section is measured by fitting the observed jet multiplicity, thereby constraining the signal and background contributions. By counting the number of b jets per event, an unconstrained value of R = 1.014 +/- 0.003 (stat.) +/- 0.032 (syst.) is measured, in a good agreement with current precision measurements in electroweak and flavour sectors. A lower limit R > 0.955 at the 95% confidence level is obtained after requiring R 0.975 is set at 95% confidence level. The result is combined with a previous CMS measurement of the t-channel single-top-quark cross section to determine the top-quark total decay width, Gamma(t) = 1.36 +/- 0.02 (stat.)(-0.11)(+0.14) (syst.) GeV
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