10,531 research outputs found
On the nucleon-nucleon interaction leading to a standing wave instability in symmetric nuclear matter
We examine a recently proposed nucleon-nucleon interaction, claimed by its
authors both realistic and leading to a standing wave instability in symmetric
nuclear matter. Contrary to these claims, we find that this interaction leads
to a serious overbinding of 4He, 16O and 40Ca nuclei when the Hartree-Fock
method is properly applied. The resulting nuclear densities contradict the
experimental data and all realistic Hartree-Fock results.Comment: 4 pages, 1 figur
A priori probability that a qubit-qutrit pair is separable
We extend to arbitrarily coupled pairs of qubits (two-state quantum systems)
and qutrits (three-state quantum systems) our earlier study (quant-ph/0207181),
which was concerned with the simplest instance of entangled quantum systems,
pairs of qubits. As in that analysis -- again on the basis of numerical
(quasi-Monte Carlo) integration results, but now in a still higher-dimensional
space (35-d vs. 15-d) -- we examine a conjecture that the Bures/SD (statistical
distinguishability) probability that arbitrarily paired qubits and qutrits are
separable (unentangled) has a simple exact value, u/(v Pi^3)= >.00124706, where
u = 2^20 3^3 5 7 and v = 19 23 29 31 37 41 43 (the product of consecutive
primes). This is considerably less than the conjectured value of the Bures/SD
probability, 8/(11 Pi^2) = 0736881, in the qubit-qubit case. Both of these
conjectures, in turn, rely upon ones to the effect that the SD volumes of
separable states assume certain remarkable forms, involving "primorial"
numbers. We also estimate the SD area of the boundary of separable qubit-qutrit
states, and provide preliminary calculations of the Bures/SD probability of
separability in the general qubit-qubit-qubit and qutrit-qutrit cases.Comment: 9 pages, 3 figures, 2 tables, LaTeX, we utilize recent exact
computations of Sommers and Zyczkowski (quant-ph/0304041) of "the Bures
volume of mixed quantum states" to refine our conjecture
On the ab initio calculation of CVV Auger spectra in closed-shell systems
We propose an ab initio method to evaluate the core-valence-valence (CVV)
Auger spectrum of systems with filled valence bands. The method is based on the
Cini-Sawatzky theory, and aims at estimating the parameters by first-principles
calculations in the framework of density-functional theory (DFT). Photoemission
energies and the interaction energy for the two holes in the final state are
evaluated by performing DFT simulations for the system with varied population
of electronic levels. Transition matrix elements are taken from atomic results.
The approach takes into account the non-sphericity of the density of states of
the emitting atom, spin-orbit interaction in core and valence, and non
quadratic terms in the total energy expansion with respect to fractional
occupation numbers. It is tested on two benchmark systems, Zn and Cu metals,
leading in both cases to L23M45M45 Auger peaks within 2 eV from the
experimental ones. Detailed analysis is presented on the relative weight of the
various contributions considered in our method, providing the basis for future
development. Especially problematic is the evaluation of the hole-hole
interaction for systems with broad valence bands: our method underestimates its
value in Cu, while we obtain excellent results for this quantity in Zn.Comment: 20 pages, 5 figures, 4 table
Rapid, multiplexed microfluidic phage display
The development of a method for high-throughput, automated proteomic screening could impact areas ranging from fundamental molecular interactions to the discovery of novel disease markers and therapeutic targets. Surface display techniques allow for efficient handling of large molecular libraries in small volumes. In particular,
phage display has emerged as a powerful technology for selecting peptides and proteins with enhanced, target-specific binding affinities. Yet, the process becomes cumbersome and time-consuming when multiple targets are involved.Here we demonstrate for the first time a microfluidic chip capable of identifying high affinity phage displayed peptides for multiple targets in just a single round and without the need for bacterial infection. The chip is shown to be able to yield well-established control consensus sequences while simultaneously
identifying new sequences for clinically important targets.
Indeed, the confined parameters of the device allow not only for highly controlled assay conditions but also introduce a significant time-reduction to the phage display process. We anticipate that this easily-fabricated, disposable device has the potential to impact areas
ranging from fundamental studies of protein, peptide, and molecular interactions, to applications such as fully automated proteomic screening
Solving the two-center nuclear shell-model problem with arbitrarily-orientated deformed potentials
A general new technique to solve the two-center problem with
arbitrarily-orientated deformed realistic potentials is demonstrated, which is
based on the powerful potential separable expansion method. As an example,
molecular single-particle spectra for C + C Mg are
calculated using deformed Woods-Saxon potentials. These clearly show that
non-axial symmetric configurations play a crucial role in molecular resonances
observed in reaction processes for this system at low energy
Electric field driven donor-based charge qubits in semiconductors
We investigate theoretically donor-based charge qubit operation driven by
external electric fields. The basic physics of the problem is presented by
considering a single electron bound to a shallow-donor pair in GaAs: This
system is closely related to the homopolar molecular ion H_2^+. In the case of
Si, heteropolar configurations such as PSb^+ pairs are also considered. For
both homopolar and heteropolar pairs, the multivalley conduction band structure
of Si leads to short-period oscillations of the tunnel-coupling strength as a
function of the inter-donor relative position. However, for any fixed donor
configuration, the response of the bound electron to a uniform electric field
in Si is qualitatively very similar to the GaAs case, with no valley quantum
interference-related effects, leading to the conclusion that electric field
driven coherent manipulation of donor-based charge qubits is feasible in
semiconductors
Volume of the quantum mechanical state space
The volume of the quantum mechanical state space over -dimensional real,
complex and quaternionic Hilbert-spaces with respect to the canonical Euclidean
measure is computed, and explicit formulas are presented for the expected value
of the determinant in the general setting too. The case when the state space is
endowed with a monotone metric or a pull-back metric is considered too, we give
formulas to compute the volume of the state space with respect to the given
Riemannian metric. We present the volume of the space of qubits with respect to
various monotone metrics. It turns out that the volume of the space of qubits
can be infinite too. We characterize those monotone metrics which generates
infinite volume.Comment: 17 page
Tight-binding parameterization for photonic band gap materials
The ideas of the linear combination of atomic orbitals (LCAO) method, well
known from the study of electrons, is extended to the classical wave case. The
Mie resonances of the isolated scatterer in the classical wave case, are
analogous to the localized eigenstates in the electronic case. The matrix
elements of the two-dimensional tight-binding (TB) Hamiltonian are obtained by
fitting to ab initio results. The transferability of the TB model is tested by
reproducing accurately the band structure of different 2D lattices, with and
without defects, thus proving that the obtained TB parameters can be used to
study other properties of the photonic band gap materials.Comment: 4 pages, 3 postscript figures, sumbitted to Phys. rev. Let
Energetics and performance of a microscopic heat engine based on exact calculations of work and heat distributions
We investigate a microscopic motor based on an externally controlled
two-level system. One cycle of the motor operation consists of two strokes.
Within each stroke, the two-level system is in contact with a given thermal
bath and its energy levels are driven with a constant rate. The time evolution
of the occupation probabilities of the two states are controlled by one rate
equation and represent the system's response with respect to the external
driving. We give the exact solution of the rate equation for the limit cycle
and discuss the emerging thermodynamics: the work done on the environment, the
heat exchanged with the baths, the entropy production, the motor's efficiency,
and the power output. Furthermore we introduce an augmented stochastic process
which reflects, at a given time, both the occupation probabilities for the two
states and the time spent in the individual states during the previous
evolution. The exact calculation of the evolution operator for the augmented
process allows us to discuss in detail the probability density for the
performed work during the limit cycle. In the strongly irreversible regime, the
density exhibits important qualitative differences with respect to the more
common Gaussian shape in the regime of weak irreversibility.Comment: 21 pages, 7 figure
- …