112,828 research outputs found
A solvable model for excitonic complexes in one dimension
It is known experimentally that stable few-body clusters containing
negatively-charged electrons (e) and positively-charged holes (h) can exist in
low-dimensional semiconductor nanostructures. In addition to the familiar
exciton (e+h), three-body 'charged excitons' (2e+h and 2h+e) have also been
observed. Much less is known about the properties of such charged excitons
since three-body problems are generally very difficult to solve, even
numerically. Here we introduce a simple model, which can be considered as an
extended Calogero model, to calculate analytically the energy spectra for both
a charged exciton and a neutral exciton in a one-dimensional nanostructure,
such as a finite-length quantum wire. Apart from its physical motivation, the
model is of mathematical interest in that it can be related to the Heun (or
Heine) equation and, as shown explicitly, highly accurate, closed form
solutions can be obtained.Comment: 14 pages, 3 figures, To appear in J. Math. Phy
On the Conjectures Regarding the 4-Point Atiyah Determinant
For the case of 4 points in Euclidean space, we present a computer aided
proof of Conjectures II and III made by Atiyah and Sutcliffe regarding Atiyah's
determinant along with an elegant factorization of the square of the imaginary
part of Atiyah's determinant
A non-Markovian optical signature for detecting entanglement in coupled excitonic qubits
We identify an optical signature for detecting entanglement in experimental
nanostructure systems comprising coupled excitonic qubits. This signature owes
its strength to non-Markovian dynamical effects in the second-order temporal
coherence function of the emitted radiation. We calculate autocorrelation and
cross-correlation functions for both selective and collective light excitation,
and prove that the coherence properties of the emitted light do indeed carry
information about the entanglement of the initial multi-qubit state.
We also show that this signature can survive in the presence of a noisy
environment.Comment: 4 pages, 4 color figures. Minor changes. Accepted version to be
published in Europhysics Letter
Simulation of Thematic Mapper performance as a function of sensor scanning parameters
The investigation and results of the Thematic Mapper Instrument Performance Study are described. The Thematic Mapper is the advanced multispectral scanner initially planned for the Earth Observation Satellite and now planned for LANDSAT D. The use of existing digital airborne scanner data obtained with the Modular Multispectral Scanner (M2S) at Bendix provided an opportunity to simulate the effects of variation of design parameters of the Thematic Mapper. Analysis and processing of this data on the Bendix Multispectral Data Analysis System were used to empirically determine categorization performance on data generated with variations of the sampling period and scan overlap parameters of the Thematic Mapper. The Bendix M2S data, with a 2.5 milliradian instantaneous field of view and a spatial resolution (pixel size) of 10-m from 13,000 ft altitude, allowed a direct simulation of Thematic Mapper data with a 30-m resolution. The flight data chosen were obtained on 30 June 1973 over agricultural test sites in Indiana
Ultrafast optical signature of quantum superpositions in a nanostructure
We propose an unambiguous signature for detecting quantum superposition
states in a nanostructure, based on current ultrafast spectroscopy techniques.
The reliable generation of such superposition states via Hadamard-like quantum
gates is crucial for implementing solid-state based quantum information
schemes. The signature originates from a remarkably strong photon antibunching
effect which is enhanced by non-Markovian dynamics.Comment: 4 pages, 2 figures. Published in Phys. Rev. B (Rapid Communications
From old wars to new wars and global terrorism
Even before 9/11 there were claims that the nature of war had changed
fundamentally. The 9/11 attacks created an urgent need to understand
contemporary wars and their relationship to older conventional and terrorist
wars, both of which exhibit remarkable regularities. The frequency-intensity
distribution of fatalities in "old wars", 1816-1980, is a power-law with
exponent 1.80. Global terrorist attacks, 1968-present, also follow a power-law
with exponent 1.71 for G7 countries and 2.5 for non-G7 countries. Here we
analyze two ongoing, high-profile wars on opposite sides of the globe -
Colombia and Iraq. Our analysis uses our own unique dataset for killings and
injuries in Colombia, plus publicly available data for civilians killed in
Iraq. We show strong evidence for power-law behavior within each war. Despite
substantial differences in contexts and data coverage, the power-law
coefficients for both wars are tending toward 2.5, which is a value
characteristic of non-G7 terrorism as opposed to old wars. We propose a
plausible yet analytically-solvable model of modern insurgent warfare, which
can explain these observations.Comment: For more information, please contact [email protected] or
[email protected]
Direct equivalence between quantum phase transition phenomena in radiation-matter and magnetic systems: scaling of entanglement
We show that the quantum phase transition arising in a standard
radiation-matter model (Dicke model) belongs to the same universality class as
the infinitely-coordinated, transverse field XY model. The effective
qubit-qubit exchange interaction is shown to be proportional to the square of
the qubit-radiation coupling. A universal finite-size scaling is derived for
the corresponding two-qubit entanglement (concurrence) and a size-consistent
effective Hamiltonian is proposed for the qubit subsystem.Comment: 4 pages, 3 figures. Minor changes. Published versio
Theory of adhesion: role of surface roughness
We discuss how surface roughness influence the adhesion between elastic
solids. We introduce a Tabor number which depends on the length scale or
magnification, and which gives information about the nature of the adhesion at
different length scales. We consider two limiting cases relevant for (a)
elastically hard solids with weak adhesive interaction (DMT-limit) and (b)
elastically soft solids or strong adhesive interaction (JKR-limit). For the
former cases we study the nature of the adhesion using different adhesive force
laws (, , where is the wall-wall separation). In
general, adhesion may switch from DMT-like at short length scales to JKR-like
at large (macroscopic) length scale. We compare the theory predictions to the
results of exact numerical simulations and find good agreement between theory
and the simulation results
Molecular dynamics study of contact mechanics: contact area and interfacial separation from small to full contact
We report a molecular dynamics study of the contact between a rigid solid
with a randomly rough surface and an elastic block with a flat surface. We
study the contact area and the interfacial separation from small contact (low
load) to full contact (high load). For small load the contact area varies
linearly with the load and the interfacial separation depends logarithmically
on the load. For high load the contact area approaches to the nominal contact
area (i.e., complete contact), and the interfacial separation approaches to
zero. The present results may be very important for soft solids, e.g., rubber,
or for very smooth surfaces, where complete contact can be reached at moderate
high loads without plastic deformation of the solids.Comment: 4 pages,5 figure
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