20,735 research outputs found
New nonlinear structures in a degenerate one-dimensional electron gas
The collective dynamics of nonlinear electron waves in an one-dimensional
degenerate electron gas is treated using the Lagrangian fluid approach. A new
class of solutions with a nontrivial space and time dependence is derived. Both
analytical and numerical results demonstrate the formation of stable,
breather-like modes, provided certain conditions are meet. For large amplitude
of the initial density perturbation, a catastrophic collapse of the plasma
density is predicted, even in the presence of the quantum statistical pressure
and quantum diffraction dispersive effects. The results are useful for the
understanding of the properties of general nonlinear structures in dense
plasmas
Many-Body Localization Transition in Random Quantum Spin Chains with Long-Range Interactions
While there are well established methods to study delocalization transitions
of single particles in random systems, it remains a challenging problem how to
characterize many body delocalization transitions. Here, we use a generalized
real-space renormalization group technique to study the anisotropic Heisenberg
model with long-range interactions, decaying with a power , which are
generated by placing spins at random positions along the chain. This method
permits a large-scale finite-size scaling analysis. We examine the full
distribution function of the excitation energy gap from the ground state and
observe a crossover with decreasing . At the full
distribution coincides with a critical function. Thereby, we find strong
evidence for the existence of a many body localization transition in disordered
antiferromagnetic spin chains with long range interactions.Comment: 6 pages, 4 figures, references adde
Relativistic Klein-Gordon-Maxwell multistream model for quantum plasmas
A multistream model for spinless electrons in a relativistic quantum plasma
is introduced by means of a suitable fluid-like version of the
Klein-Gordon-Maxwell system. The one and two-stream cases are treated in
detail. A new linear instability condition for two-stream quantum plasmas is
obtained, generalizing the previously known non-relativistic results. In both
the one and two-stream cases, steady-state solutions reduce the model to a set
of coupled nonlinear ordinary differential equations, which can be numerically
solved, yielding a manifold of nonlinear periodic and soliton structures. The
validity conditions for the applicability of the model are addressed
Challenges arising from alternative investment management.
Alternative investment management differs from traditional asset management in a number of respects. First, it is distinct in terms of both its targets â aiming to achieve an absolute performance, regardless of trends in underlying markets â and its strategies, in particular exploiting inefficiencies in the valuation of financial assets via opportunistic and discretionary positions. It also differs in terms of the financial techniques implemented, e.g. the extensive use made of leverage, derivatives and short selling, and the specific investment vehicles used (ad hoc structures such as hedge funds that are not bound by ordinary law in the way traditional investment vehicles are). These particularities, alongside the fact that the alternative investment universe is somewhat opaque, make it difficult to measure a fundâs risks or a fund managerâs performance. Specific measurement tools are therefore required, which differ from those commonly used in traditional asset management. Over the past few years, the alternative investment management, a diverse and rapidly-evolving universe, has enjoyed a spectacular development, which is illustrated by the sharp rise in the amounts under management and the proliferation of investment vehicles offered to an increasingly broad investor base. In view of the specific nature of alternative fund managersâ modus operandi, the flourishing of the alternative investment industry raises questions as to its implications in terms of financial stability. It also raises new issues regarding the division of roles between market participants and supervisory authorities in the organisation and monitoring of this asset management sector.
Disordered Quantum Spin Chains with Long-Range Antiferromagnetic Interactions
We investigate the magnetic susceptibility of quantum spin chains
of spins with power-law long-range antiferromagnetic coupling as a
function of their spatial decay exponent and cutoff length . The
calculations are based on the strong disorder renormalization method which is
used to obtain the temperature dependence of and distribution
functions of couplings at each renormalization step. For the case with only
algebraic decay () we find a crossover at
between a phase with a divergent low-temperature susceptibility
for to a phase with a vanishing
for . For finite cutoff lengths
, this crossover occurs at a smaller . Additionally we
study the localization of spin excitations for by evaluating
the distribution function of excitation energies and we find a delocalization
transition that coincides with the opening of the pseudo-gap at
.Comment: 6 pages, 7 figure
Bose-Glass Phases in Disordered Quantum Magnets
In disordered spin systems with antiferromagnetic Heisenberg exchange,
transitions into and out of a magnetic-field-induced ordered phase pass through
a unique regime. Using quantum Monte Carlo simulations to study the
zero-temperature behavior, these intermediate regions are determined to be a
Bose-Glass phase. The localization of field-induced triplons causes a finite
compressibility and hence glassiness in the disordered phase.Comment: 4 pages, 4 figure
The uniting of Europe and the foundation of EU studies: revisiting the neofunctionalism of Ernst B. Haas
This article suggests that the neofunctionalist theoretical legacy left by Ernst B. Haas is somewhat richer and more prescient than many contemporary discussants allow. The article develops an argument for routine and detailed re-reading of the corpus of neofunctionalist work (and that of Haas in particular), not only to disabuse contemporary students and scholars of the normally static and stylized reading that discussion of the theory provokes, but also to suggest that the conceptual repertoire of neofunctionalism is able to speak directly to current EU studies and comparative regionalism. Neofunctionalism is situated in its social scientific context before the theory's supposed erroneous reliance on the concept of 'spillover' is discussed critically. A case is then made for viewing Haas's neofunctionalism as a dynamic theory that not only corresponded to established social scientific norms, but did so in ways that were consistent with disciplinary openness and pluralism
Fidelity approach to the disordered quantum XY model
We study the random XY spin chain in a transverse field by analyzing the
susceptibility of the ground state fidelity, numerically evaluated through a
standard mapping of the model onto quasi-free fermions. It is found that the
fidelity susceptibility and its scaling properties provide useful information
about the phase diagram. In particular it is possible to determine the Ising
critical line and the Griffiths phase regions, in agreement with previous
analytical and numerical results.Comment: 4 pages, 3 figures; references adde
Lever, alvleesklier en SLE
Systemische lupus erythematosus (SLE) is een auto-immuunziekte, die in Nederland bij 1 op de 1000 personen voorkomt. Als gevolg van de ziektekomen in verschillende organen ontstekingsprocessen voor. Aangedane organen kunnen onder andere de longen, het hart, de huid en de gewrichten zijn. Wat de oorzaak van deze ontstekingsprocessen is, is niet bekend. Over de ontstekingsprocessen wordt veel gepubliceerd.
De Nederlandse Vereniging van Lupus Erythematosus patiënten (N.V.L.E.) komt in de praktijk regelmatig mensen tegen met SLE die tevens een lever- en/of alvleesklieraandoening hebben. Door de N.V.L.E wordt de vraag gesteld aan de wetenschapswinkel of er ook literatuur bekend is over aandoe- ningen aan de lever en alvleesklier bij SLE. Bij hen is hier geen literatuur over bekend.
In dit overzicht wordt een korte weergave gegeven van wat er over lever- en alvlees- klieraandoeningen bij SLE bekend is. Om literatuur over dit onderwerp te vinden is gezocht in de algemene leerboeken over reumatologische ziekten. De informatie die gegeven wordt is niet erg specifiek. In Medline is daarna gezocht naar verdere literatuur over dit onderwerp.
Aan de hand van algemene uitleg over de werking van de lever en de alvleesklier, zal eerst wat worden gezegd over de lever en SLE, daarna over de alvleesklier en SLE.
Aan het eind van de afzonderlijke stukjes over lever en alvleesklier is de gebruikte literatuur weergegeven.
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