195 research outputs found
Capacitated Vehicle Routing with Non-Uniform Speeds
The capacitated vehicle routing problem (CVRP) involves distributing
(identical) items from a depot to a set of demand locations, using a single
capacitated vehicle. We study a generalization of this problem to the setting
of multiple vehicles having non-uniform speeds (that we call Heterogenous
CVRP), and present a constant-factor approximation algorithm.
The technical heart of our result lies in achieving a constant approximation
to the following TSP variant (called Heterogenous TSP). Given a metric denoting
distances between vertices, a depot r containing k vehicles with possibly
different speeds, the goal is to find a tour for each vehicle (starting and
ending at r), so that every vertex is covered in some tour and the maximum
completion time is minimized. This problem is precisely Heterogenous CVRP when
vehicles are uncapacitated.
The presence of non-uniform speeds introduces difficulties for employing
standard tour-splitting techniques. In order to get a better understanding of
this technique in our context, we appeal to ideas from the 2-approximation for
scheduling in parallel machine of Lenstra et al.. This motivates the
introduction of a new approximate MST construction called Level-Prim, which is
related to Light Approximate Shortest-path Trees. The last component of our
algorithm involves partitioning the Level-Prim tree and matching the resulting
parts to vehicles. This decomposition is more subtle than usual since now we
need to enforce correlation between the size of the parts and their distances
to the depot
Magnetic-field-induced Luttinger liquid
It is shown that a strong magnetic field applied to a bulk metal induces a
Luttinger-liquid phase. This phase is characterized by the zero-bias anomaly in
tunneling: the tunneling conductance scales as a power-law of voltage or
temperature. The tunneling exponent increases with the magnetic field as BlnB.
The zero-bias anomaly is most pronounced for tunneling with the field applied
perpendicular to the plane of the tunneling junction.Comment: a reference added, minor typos correcte
The Influence of In Vitro Gastrointestinal Digestion on the Anticancer Activity of Manuka Honey
Manuka honey (MH) is a natural food with many beneficial properties to human health,
thanks to its high variety of bioactive compounds; however, little is known about its bioaccessibility.
The aim of this study was to evaluate and compare the polyphenol compounds, the antioxidant
capacity and the anticancer activity of MH subjected to an in vitro gastrointestinal digestion in human
HCT-116 colon cancer cells. Raw MH and digested MH (DMH) were assessed for total polyphenols
and flavonoids by spectrophotometric and HPLC-ESI-MS/MS analysis, and total antioxidant capacity
(TAC) using different methods. Cell viability, intracellular ROS production, apoptosis, cell cycle and
colony formation capacity were tested after treatment with MH or DMH. Results showed that total
polyphenols, total flavonoids and TAC were significantly (p < 0.05) reduced after in vitro digestion.
In addition, MH and DMH at 8, 16 and 24 mg/mL had similar effects in inducing intracellular ROS
production and in inhibiting the colon formation ability; MH induced a more marked apoptosis
compared to DMH, while cell cycle was blocked in S phase by MH and in Sub G1 phase by DMH.
Our results increase knowledge of the effect of gastrointestinal digestion on the biological effect of
honey against colorectal cancer
Differential Photoelectron Holography: A New Approach for Three-Dimensional Atomic Imaging
We propose differential holography as a method to overcome the long-standing
forward-scattering problem in photoelectron holography and related techniques
for the three-dimensional imaging of atoms. Atomic images reconstructed from
experimental and theoretical Cu 3p holograms from Cu(001) demonstrate that this
method suppresses strong forward-scattering effects so as to yield more
accurate three-dimensional images of side- and back-scattering atoms.Comment: revtex, 4 pages, 2 figure
Electron Correlation Effects in Resonant Inelastic X-ray Scattering of NaV2O5
Element- and site-specific resonant inelastic x-ray scattering spectroscopy
(RIXS) is employed to investigate electron correlation effects in {}. In contrast to single photon techniques, RIXS at the vanadium
edge is able to probe transitions between V d-bands. A sharp energy
loss feature is observed at -1.56 eV, which is well reproduced by a model
calculation including correlation effects. The calculation identifies the loss
feature as excitation between the lower and upper Hubbard bands and permits an
accurate determination of the Hubbard interaction term eV.Comment: 15 pages, four figures, accepted to Phys. Rev. Let
Spin-Peierls transition in NaV2O5 in high magnetic fields
We investigate the magnetic field dependence of the spin-Peierls transition
in NaVO in the field range 16T-30T. The transition temperature exhibits
a very weak variation with the field, suggesting a novel mechanism for the
formation of the spin-Peierls state. We argue that a charge ordering transition
accompanied by singlet formation is consistent with our observations.Comment: 4 pages, 3 figures, final version to appear in Phys. Rev. B (RC
- …