Pascal-orientated computer design

Imperial Users onl

A Modeling approach for analysis and improvement of spindle-holder-tool assembly dynamics

The most important information required for chatter stability analysis is the dynamics of the involved structures, i.e. the frequency response functions (FRFs) which are usually determined experimentally. In this study, the tool point FRF of a spindle-holder-tool assembly is analytically determined by using the receptance coupling and structural modification techniques. Timoshenko’s beam model is used for increased accuracy. The spindle is also modeled analytically with elastic supports representing the bearings. The mathematical model is used to determine the effects of different parameters on the tool point FRF and to identify contact dynamics from experimental measurements. The applications of the model are demonstrated and the predictions are verified experimentally

Optical spectroscopy study on pressure-induced phase transitions in the three-dimensional Dirac semimetal Cd3_3As2_2

We report a room-temperature optical reflectivity study performed on [112]-oriented Cd$_3$As$_2$ single crystals over a broad energy range under external pressure up to 10 GPa. The abrupt drop of the band dispersion parameter ($z$-parameter) and the interruption of the gradual redshift of the bandgap at $\sim$4~GPa confirms the structural phase transition from a tetragonal to a monoclinic phase in this material. The pressure-induced increase of the overall optical conductivity at low energies and the continuous redshift of the high-energy bands indicate that the system evolves towards a topologically trivial metallic state, although a complete closing of the band gap could not be observed in the studied pressure range. Furthermore, a detailed investigation of the low-pressure regime suggests the possible existence of an intermediate state between 2 and 4~GPa , that might be a precursor of the structural phase transition or due to the lifted degeneracy of the Dirac nodes. Several optical parameters show yet another anomaly at 8~GPa, where low-temperature superconductivity was found in an earlier study.Comment: submitted to PR

Competitive pressure and labor productivity: world iron ore markets in the 1980s

Does the extent of competitive pressure industries face influence their productivity? We study a natural experiment conducted in the iron ore industry as a result of the collapse in world steel production in the early 1980s. For iron ore producers, whose only market is the steel industry, this collapse was an exogenous shock. The drop in steel production differed dramatically by region: it fell by about a third in the Atlantic Basin but only very little in the Pacific Basin. Given that the cost of transporting iron ore is very high relative to its mine value, Atlantic iron ore producers faced a much greater increase in competitive pressure than did Pacific iron ore producers. In response to the crisis, most Atlantic iron ore producers doubled their labor productivity; Pacific iron ore producers experienced few productivity gains. ; This article originally appeared in the American Economic Review. (c) American Economic Association.Labor productivity ; Steel industry and trade

Latin America in the rearview mirror

Latin American countries are the only Western countries that are poor and that aren't gaining ground on the United States. This paper evaluates why Latin America has not replicated Western economic success. We find that this failure is primarily due to TFP differences. Latin America's TFP gap is not plausibly accounted for by human capital differences, but rather reflects inefficient production. We argue that competitive barriers are a promising channel for understanding low Latin TFP. We document that Latin America has many more international and domestic competitive barriers than do Western and successful East Asian countries. We also document a number of microeconomic cases in Latin America in which large reductions in competitive barriers increase productivity to Western levels.Latin America - Economic conditions

Latin America in the Rearview Mirror

Latin American countries are the only Western countries that are poor and that aren't gaining ground on the United States. This paper evaluates why Latin America has not replicated Western economic success. We find that this failure is primarily due to TFP differences. Latin America's TFP gap is not plausibly accounted for by human capital differences, but rather reflects inefficient production. We argue that competitive barriers are a promising channel for understanding low Latin TFP. We document that Latin America has many more international and domestic competitive barriers than do Western and successful East Asian countries. We also document a number of microeconomic cases in Latin America in which large reductions in competitive barriers increase productivity to Western levels.

Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers

We present a comprehensive study of the exchange bias effect in a model system. Through numerical analysis of the exchange bias and coercive fields as a function of the antiferromagnetic layer thickness we deduce the absolute value of the averaged anisotropy constant of the antiferromagnet. We show that the anisotropy of IrMn exhibits a finite size effect as a function of thickness. The interfacial spin disorder involved in the data analysis is further supported by the observation of the dual behavior of the interfacial uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we have observed that the antiferromagnetic uncompensated spins are dominantly frozen with nearly no rotating spins due to the chemical intermixing, which correlates to the inferred mechanism for the exchange bias.Comment: 4 pages, 3 figure

Mott-Hubbard exciton in the optical conductivity of YTiO3 and SmTiO3

In the Mott-Hubbard insulators YTiO3 and SmTiO3 we study optical excitations from the lower to the upper Hubbard band, d^1d^1 -> d^0d^2. The multi-peak structure observed in the optical conductivity reflects the multiplet structure of the upper Hubbard band in a multi-orbital system. Absorption bands at 2.55 and 4.15 eV in the ferromagnet YTiO3 correspond to final states with a triplet d^2 configuration, whereas a peak at 3.7 eV in the antiferromagnet SmTiO3 is attributed to a singlet d^2 final state. A strongly temperature-dependent peak at 1.95 eV in YTiO3 and 1.8 eV in SmTiO3 is interpreted in terms of a Hubbard exciton, i.e., a charge-neutral (quasi-)bound state of a hole in the lower Hubbard band and a double occupancy in the upper one. The binding to such a Hubbard exciton may arise both due to Coulomb attraction between nearest-neighbor sites and due to a lowering of the kinetic energy in a system with magnetic and/or orbital correlations. Furthermore, we observe anomalies of the spectral weight in the vicinity of the magnetic ordering transitions, both in YTiO3 and SmTiO3. In the G-type antiferromagnet SmTiO3, the sign of the change of the spectral weight at T_N depends on the polarization. This demonstrates that the temperature dependence of the spectral weight is not dominated by the spin-spin correlations, but rather reflects small changes of the orbital occupation.Comment: Strongly extended version; new data of SmTiO3 included; detailed discussion of temperature dependence include