35,716 research outputs found
Dimensional-scaling estimate of the energy of a large system from that of its building blocks: Hubbard model and Fermi liquid
A simple, physically motivated, scaling hypothesis, which becomes exact in
important limits, yields estimates for the ground-state energy of large,
composed, systems in terms of the ground-state energy of its building blocks.
The concept is illustrated for the electron liquid, and the Hubbard model. By
means of this scaling argument the energy of the one-dimensional half-filled
Hubbard model is estimated from that of a 2-site Hubbard dimer, obtaining
quantitative agreement with the exact one-dimensional Bethe-Ansatz solution,
and the energies of the two- and three-dimensional half-filled Hubbard models
are estimated from the one-dimensional energy, recovering exact results for
and and coming close to Quantum Monte Carlo data for
intermediate .Comment: 3 figure
Suppression of two-bounce windows in kink-antikink collisions
We consider a class of topological defects in -dimensions with a
deformed kink structure whose stability analysis leads to a
Schr\"odinger-like equation with a zero-mode and at least one vibrational
(shape) mode. We are interested in the dynamics of kink-antikink collisions,
focusing on the structure of two-bounce windows. For small deformation and for
one or two vibrational modes, the observed two-bounce windows are explained by
the standard mechanism of a resonant effect between the first vibrational and
the translational modes. With the increasing of the deformation, the effect of
the appearance of more than one vibrational mode is the gradual disappearance
of the initial two-bounce windows. The total suppression of two-bounce windows
even with the presence of a vibrational mode offers a counterexample from what
expected from the standard mechanism. For even larger deformation, some
two-bounce windows reappear, but with a non-standard structure.Comment: 13 pages, 6 figure
Non-Gaussian two-mode squeezing and continuous variable entanglement of linearly and circularly polarized light beams interacting with cold atoms
We investigate how entangled coherent states and superpositions of low
intensity coherent states of non-Gaussian nature can be generated via
non-resonant interaction between either two linearly or circularly polarized
field modes and an ensemble of X-like four-level atoms placed in an optical
cavity. We compare our results to recent experimental observations and argue
that the non-Gaussian structure of the field states may be present in those
systems.Comment: 10 pages, 7 figures, replaced with final published versio
The use of genes for performance enhancement: doping or therapy?
Recent biotechnological advances have permitted the manipulation of genetic sequences to treat several diseases in a process called gene therapy. However, the advance of gene therapy has opened the door to the possibility of using genetic manipulation (GM) to enhance athletic performance. In such âgene dopingâ, exogenous genetic sequences are inserted into a specific tissue, altering cellular gene activity or leading to the expression of a protein product. The exogenous genes most likely to be utilized for gene doping include erythropoietin (EPO), vascular endothelial growth factor (VEGF), insulin-like growth factor type 1 (IGF-1), myostatin antagonists, and endorphin. However, many other genes could also be used, such as those involved in glucose metabolic pathways. Because gene doping would be very difficult to detect, it is inherently very attractive for those involved in sports who are prepared to cheat. Moreover, the field of gene therapy is constantly and rapidly progressing, and this is likely to generate many new possibilities for gene doping. Thus, as part of the general fight against all forms of doping, it will be necessary to develop and continually improve means of detecting exogenous gene sequences (or their products) in athletes. Nevertheless, some bioethicists have argued for a liberal approach to gene doping
Genuine Multipartite Entanglement in Quantum Phase Transitions
We demonstrate that the Global Entanglement (GE) measure defined by Meyer and
Wallach, J. Math. Phys. 43, 4273 (2002), is maximal at the critical point for
the Ising chain in a transverse magnetic field. Our analysis is based on the
equivalence of GE to the averaged linear entropy, allowing the understanding of
multipartite entanglement (ME) features through a generalization of GE for
bipartite blocks of qubits. Moreover, in contrast to GE, the proposed ME
measure can distinguish three paradigmatic entangled states: ,
, and . As such the generalized measure can detect
genuine ME and is maximal at the critical point.Comment: 4 pages, 3 figures. Replaced with final published versio
Exploring microfoundations and multilevel mechanisms of absorptive capacity in an emerging economy: empirical evidence from a leading car manufacturer
Purpose
Despite the importance of knowledge processes in building absorptive capacity, we are less clear about the micro-processes of absorptive capacity development and particularly about the role of individualsâ knowledge processes.
Design/methodology/approach
This study empirically examined, via an in-depth case study, the microfoundations of absorptive capacity and their influence on building absorptive capacity in an automaker across the course of four product innovation projects.
Findings
Findings suggested that dynamics in a knowledge environment informed individual-level tacit and explicit knowledge processes. In return, knowledge processes at the individual level informed organizational learning processes and the emergence of knowledge processes at organization level for acquisition, assimilation, transformation, and exploitation of new knowledge.
Originality
This study contributes to the literature by revealing individualsâ knowledge processes from which absorptive capacity emerges. Practically, managers can use the findings of this study to promote certain knowledge processes to develop intended aspects of absorptive capacity at an individual level
Photoassociative ionization of Na inside a storage ring
Motivated by recent interest in low dimensional arrays of atoms, we
experimentally investigated the way cold collisional processes are affected by
the geometry of the considered atomic sample. More specifically, we studied the
case of photoassociative ionization (PAI) both in a storage ring where
collision is more unidirectional in character and in a trap with clear
undefinition of collision axis. First, creating a ring shaped trap (atomotron)
we investigated two-color PAI dependence with intensity and polarization of a
probing laser. The intensity dependence of the PAI rate was also measured in a
magneto-optical trap presenting equivalent temperature and density conditions.
Indeed, the results show that in the ring trap, the value of the PAI rate
constant is much lower and does not show evidences of saturation, unlike in the
case of the 3D-MOT. Cold atomic collisions in storage ring may represent new
possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio
Behavior of the Dripping Faucet over a Wide Range of the Flow Rate
The time interval of successive water-drips from a faucet was examined over a
wide range of the flow rate. The dripping interval alternately exhibits a
stable state and a chaotic state as the flow rate increases. In the stable
state, the volume of the drip is kept constant at fixed flow rates, and the
constant volume increases with the flow rate. In the chaotic state, in addition
to a mechanics that the drip is torn by its own weight, the vibration of the
drip on the faucet takes part in the strange behavior of the interval.Comment: 7 pages, 7 figures, to be published in J. Phys. Soc. Jpn vol
68-2(1999
Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited
Water activity and its relationship with interactions stabilising lamellar
stacks of mixed lipid bilayers in their fluid state are investigated by means
of osmotic pressure measurements coupled with small-angle x-ray scattering. The
(electrically-neutral) bilayers are composed of a mixture in various
proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic
cosurfactant with an ethoxylated polar head. For highly dehydrated samples the
osmotic pressure profile always exhibits the "classical" exponential decay as
hydration increases but, depending on Simulsol to lecithin ratio, it becomes
either of the "bound" or "unbound" types for more water-swollen systems. A
simple thermodynamic model is used for interpreting the results without
resorting to the celebrated but elusive "hydration forces"Comment: 24 pages, 12 figures. Accepted for publication in The European
Physical Journal
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