67,690 research outputs found
Linear Response of One-Dimensional Liquid 4He to External Perturbations
No full textWe study the response of one-dimensional liquid (Formula presented.) to weak perturbations relying on the dynamical structure factor, (Formula presented.), recently obtained via ab-initio techniques (Bertaina et al. in Phys Rev Lett 116:135302, 2016). We evaluate the drag force, (Formula presented.), experienced by an impurity moving along the system with velocity v and the static response function, (Formula presented.), describing the density modulations induced by a periodic perturbation with wave vector q
Dynamical correlations in one-dimensional 4He beyond Luttinger theory
No full textWe study a collection of He atoms confined to strictly one dimension at zero temperature. We use the exact Path Integral Ground State method to evaluate the equation of state and the radial distribution function, and we find that the system behaves as a Luttinger liquid with parameter that takes all the possible values , depending on the density , being the He mass and the sound velocity\cite{uno}. Actually the system goes from in the high density quasi--solid regime to close to the low density spinodal decomposition. By inverting the imaginary--time intermediate scattering function with the Genetic Inversion via Falsification of Theories method\cite{due}, we also evaluate the dynamical structure factor in the whole range in , exploring the behavior of the dynamical correlations beyond the limits of applicability of Luttinger liquid theory. We find that the famous phonon--maxon--roton excitation spectrum of He is not present in 1D. On the contrary, manifests a particle--hole continuum typical of a fermionic system, as expected from the Bose-Fermi mapping valid for 1D hard-core interactions. In qualitative agreement with recent non--linear Luttinger liquid theories, we find that the main weight of density fluctuations continuously shifts from the lower threshold branch in the quasi--solid regime, to the upper Bogoliubov branch in the compressible low--density regime. At an intermediate density near \AA, the system corresponds to and maps to a non interacting Fermi gas at very low energies , while at higher energies display non--universal effects depending on the He interaction potential
Implementation of the linear method for the optimization of Jastrow-Feenberg and backflow correlations
No full textWe present a fully detailed and highly performing implementation of the Linear Method (Toulouse and Umrigar, 2007) to optimize Jastrow-Feenberg and Backflow Correlations in many-body wave-functions, which are widely used in condensed matter physics. We show that it is possible to implement such optimization scheme performing analytical derivatives of the wave-function with respect to the variational parameters achieving the best possible complexity O(N3) in the number of particles N
Microscopic Study of Static and Dynamical Properties of Dilute One-Dimensional Soft Bosons
No full textWe study static properties and the dynamical structure factor of zero-temperature dilute bosons interacting via a soft-shoulder potential in one dimension. Our approach is fully microscopic and employs state-of-the-art quantum Monte Carlo and analytic continuation techniques. By increasing the interaction strength, our model reproduces the Lieb–Liniger gas, the Tonks–Girardeau and the hard-rods models
One-dimensional liquid He 4: dynamical properties beyond Luttinger-Liquid theory
No full textWe compute the zero-temperature dynamical structure factor of one-dimensional liquid He4 by means of state-of-the-art quantum Monte Carlo and analytic continuation techniques. By increasing the density, the dynamical structure factor reveals a transition from a highly compressible critical liquid to a quasisolid regime. In the low-energy limit, the dynamical structure factor can be described by the quantum hydrodynamic Luttinger-liquid theory, with a Luttinger parameter spanning all possible values by increasing the density. At higher energies, our approach provides quantitative results beyond the Luttinger-liquid theory. In particular, as the density increases, the interplay between dimensionality and interaction makes the dynamical structure factor manifest a pseudo-particle-hole continuum typical of fermionic systems. At the low-energy boundary of such a region and moderate densities, we find consistency, within statistical uncertainties, with predictions of a power-law structure by the recently developed nonlinear Luttinger-liquid theory. In the quasisolid regime, we observe a novel behavior at intermediate momenta, which can be described by new analytical relations that we derive for the hard-rods model
Dynamical structure factor of one-dimensional hard rods
No full textThe zero-temperature dynamical structure factor of one-dimensional hard rods is computed
using state-of-the-art quantum Monte Carlo and analytic continuation techniques, complemented by a Bethe Ansatz analysis.
As the density increases, reveals a crossover from the Tonks-Girardeau gas to a
quasi-solid regime, along which the low-energy properties are found
in agreement with the nonlinear Luttinger liquid theory. Our quantitative estimate of extends beyond the low-energy limit and confirms a theoretical prediction regarding the behavior
of at specific wavevectors , where is the core radius,
resulting from the interplay of the particle-hole boundaries of
suitably rescaled ideal Fermi gases. We observe significant
similarities between hard rods and one-dimensional He at high density,
suggesting that the hard-rods model may provide an accurate description of
dense one-dimensional liquids of quantum particles interacting through a strongly repulsive, finite-range potential
Mining e-mail content for author identification forensics
No full textWe describe an investigation into e-mail content mining for author identification, or authorship attribution, for the purpose of forensic investigation. We focus our discussion on the ability to discriminate between authors for the case of both aggregated e-mail topics as well as across different email topics. An extended set of e-mail document features including structural characteristics and linguistic patterns were derived and, together with a Support Vector Machine learning algorithm, were used for mining the e-mail content. Experiments using a number of e-mail documents generated by different authors on a set of topics gave promising results for both aggregated and multi-topic author categorisation
Cord blood transplantation in children with haematological malignancies
No full textUmbilical cord blood transplantation (UCBT) is largely used to treat children affected by haematological malignant disorders. In comparison to bone marrow transplantation (BMT), advantages of UCBT include lower incidence and severity of graft-versus-host disease, easier procurement and prompter availability of cord blood cells, and the possibility of using donors having HLA disparities with the recipient. The large experience accumulated so far has shown that UCBT offers to children a probability of cure at least comparable to that of patients transplanted with bone marrow cells. Since it has been demonstrated that an inverse correlation between the number of nucleated cord blood cells infused per kg recipient body weight and the risk of dying for transplantation-related causes exists, recently developed strategies aimed at increasing the number of cord blood progenitors and at favouring stem cell homing could further optimize the outcome of children with leukemia or other malignancies receiving UCBT. © 2010 Elsevier Ltd. All rights reserved
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
- …
