547 research outputs found
Oblique triangular antiferromagnetic phase in CsCuCoCl
The spin-1/2 stacked triangular antiferromagnet CsCuCoCl with
undergoes two phase transitions at zero field. The
low-temperature phase is produced by the small amount of Co doping. In
order to investigate the magnetic structures of the two ordered phases, the
neutron elastic scattering experiments have been carried out for the sample
with . It is found that the intermediate phase is identical to
the ordered phase of CsCuCl, and that the low-temperature phase is an
oblique triangular antiferromagnetic phase in which the spins form a triangular
structure in a plane tilted from the basal plane. The tilting angle which is
42 at K decreases with increasing temperature, and becomes
zero at K. An off-diagonal exchange term is proposed as the
origin of the oblique phase.Comment: 6 pages, 7 figure
Thermochemical scanning probe lithography of protein gradients at the nanoscale
Patterning nanoscale protein gradients is crucial for studying a variety of cellular processes in vitro. Despite the recent development in nano-fabrication technology, combining nanometric resolution and fine control of protein concentrations is still an open challenge. Here, we demonstrate the use of thermochemical scanning probe lithography (tc-SPL) for defining micro- and nano-sized patterns with precisely controlled protein concentration. First, tc-SPL is performed by scanning a heatable atomic force microscopy tip on a polymeric substrate, for locally exposing reactive amino groups on the surface, then the substrate is functionalized with streptavidin and laminin proteins. We show, by fluorescence microscopy on the patterned gradients, that it is possible to precisely tune the concentration of the immobilized proteins by varying the patterning parameters during tc-SPL. This paves the way to the use of tc-SPL for defining protein gradients at the nanoscale, to be used as chemical cues e.g. for studying and regulating cellular processes in vitro
Symmetric generation of Coxeter groups
We provide involutory symmetric generating sets of finitely generated Coxeter
groups, fulfilling a suitable finiteness condition, which in particular is
fulfilled in the finite, affine and compact hyperbolic cases.Comment: 11 pages, 11 figure
Processing of ultrafine-size particulate metal matrix composites by advanced shear technology
Copyright @ 2009 ASM International. This paper was published in Metallurgical & Materials Transactions A 40A(3) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.Lack of efficient mixing technology to achieve a uniform distribution of fine-size reinforcement within the matrix and the high cost of producing components have hindered the widespread adaptation of particulate metal matrix composites (PMMCs) for engineering applications. A new rheo-processing method, the melt-conditioning high-pressure die-cast (MC-HPDC) process, has been developed for manufacturing near-net-shape components of high integrity. The MC-HPDC process adapts the well-established high shear dispersive mixing action of a twin-screw mechanism to the task of overcoming the cohesive force of the agglomerates under a high shear rate and high intensity of turbulence. This is followed by direct shaping of the slurry into near-net-shape components using an existing cold-chamber die-casting process. The results indicate that the MC-HPDC samples have a uniform distribution of ultrafine-sized SiC particles throughout the entire sample in the as-cast condition. Compared to those produced by conventional high-pressure die casting (HPDC), MC-HPDC samples have a much improved tensile strength and ductility.EP-SR
Essays in international trade and organisational economics
This thesis contains three chapters that examine various facets of how the market and technological environment shapes firms – and how firms shape their environments.
The first chapter studies how multinational manufacturing firms organise production in parallel processing supply chains. Using confidential data on international sourcing of French manufacturing firms and an instrumental variables strategy based on selfconstructed input-output tables, the chapter shows that inputs that account for a high cost share – i.e. that are more important for technological reasons – are more likely to be produced by a multinational for itself, while unimportant ones are outsourced to third parties. It provides additional empirical evidence that this main finding is consistent with a property rights model of the boundary of the firm.
The second chapter produces empirical facts on how exogenous changes in tariffs on intermediate goods have affected vertical integration patterns in France over the period 1996-2006 and evaluates them in light of the current literature. Using a long differences approach and detailed information on supply relationships, it shows that more protectionist policies by other countries and by the EU discouraged integrated relationships from shifting towards outsourcing and that initial market structure mattered for the impact of trade policy.
The third chapter provides rare causal evidence for the relevance of endowment driven comparative advantage. It uses the fracking boom in the US following 2006 as a source of exogenous variation in the endowment of natural gas – and therefore in energy: fracking made energy considerably cheaper in the US compared to the rest of the world. The chapter studies factor, output, and international trade responses across sectors. It finds that energy intensive sectors expand along all dimensions and, most importantly, export more, which validates one of the most important neo-classical theories of why countries trade with each other
Non-perturbative Propagators, Running Coupling and Dynamical Quark Mass of Landau gauge QCD
The coupled system of renormalized Dyson-Schwinger equations for the quark,
gluon and ghost propagators of Landau gauge QCD is solved within truncation
schemes. These employ bare as well as non-perturbative ansaetze for the
vertices such that the running coupling as well as the quark mass function are
independent of the renormalization point. The one-loop anomalous dimensions of
all propagators are reproduced. Dynamical chiral symmetry breaking is found,
the dynamically generated quark mass agrees well with phenomenological values
and corresponding results from lattice calculations. The effects of unquenching
the system are small. In particular the infrared behavior of the ghost and
gluon dressing functions found in previous studies is almost unchanged as long
as the number of light flavors is smaller than four.Comment: 34 pages, 10 figures, version to be published by Phys. Rev.
Renormalization and Chiral Symmetry Breaking in Quenched QED in Arbitrary Covariant Gauge
We extend a previous Landau-gauge study of subtractive renormalization of the
fermion propagator Dyson-Schwinger equation (DSE) in strong-coupling, quenched
QED_4 to arbitrary covariant gauges. We use the fermion-photon proper vertex
proposed by Curtis and Pennington with an additional correction term included
to compensate for the small gauge-dependence induced by the ultraviolet
regulator. We discuss the chiral limit and the onset of dynamical chiral
symmetry breaking in the presence of nonperturbative renormalization. We
extract the critical coupling in several different gauges and find evidence of
a small residual gauge-dependence in this quantity.Comment: REVTEX 3.0, 27 pages including 14 Extended Postscript files
comprising 9 figures. Replacement: discussion of chiral limit corrected, and
some minor typographical errors fixed. To appear in Phys. Rev.
Theoretical prediction of CNT-CF/PP composite tensile properties using various numerical modeling methods
Development of effective models to predict tensile properties of ‘carbon nanotube coated carbon fibre reinforced polypropylene (CNT-CF/PP)’ composites is briefly discussed. The composite taken as the reference is based on the highest growth mechanism of CNTs over carbon fibres. Halpin-Tsai and Combined Voigt-Reuss model has been implemented. Young's modulus for CNT-CF/PP composites has been found 4.5368 GPa and the tensile strength has been estimated 45.367 MPa considering the optimum operating condition of chemical vapor deposition (CVD) technique. Stiffness of the composite is represented through the stress-strain plots; stiffness is proportional to the steepness of the slope. There are slight deviations of results that have been found theoretically over the experimental issues
Analytic properties of the Landau gauge gluon and quark propagators
We explore the analytic structure of the gluon and quark propagators of
Landau gauge QCD from numerical solutions of the coupled system of renormalized
Dyson--Schwinger equations and from fits to lattice data. We find sizable
negative norm contributions in the transverse gluon propagator indicating the
absence of the transverse gluon from the physical spectrum. A simple analytic
structure for the gluon propagator is proposed. For the quark propagator we
find evidence for a mass-like singularity on the real timelike momentum axis,
with a mass of 350 to 500 MeV. Within the employed Green's functions approach
we identify a crucial term in the quark-gluon vertex that leads to a positive
definite Schwinger function for the quark propagator.Comment: 42 pages, 16 figures, revtex; version to be published in Phys Rev
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