30,645 research outputs found
Measurement of Scattering Rate and Minimum Conductivity in Graphene
The conductivity of graphene samples with various levels of disorder is
investigated for a set of specimens with mobility in the range of
cm/V sec. Comparing the experimental data with the
theoretical transport calculations based on charged impurity scattering, we
estimate that the impurity concentration in the samples varies from cm. In the low carrier density limit, the conductivity exhibits
values in the range of , which can be related to the residual
density induced by the inhomogeneous charge distribution in the samples. The
shape of the conductivity curves indicates that high mobility samples contain
some short range disorder whereas low mobility samples are dominated by long
range scatterers.Comment: 4 pages 4 figure
Three fermions in a box at the unitary limit: universality in a lattice model
We consider three fermions with two spin components interacting on a lattice
model with an infinite scattering length. Low lying eigenenergies in a cubic
box with periodic boundary conditions, and for a zero total momentum, are
calculated numerically for decreasing values of the lattice period. The results
are compared to the predictions of the zero range Bethe-Peierls model in
continuous space, where the interaction is replaced by contact conditions. The
numerical computation, combined with analytical arguments, shows the absence of
negative energy solution, and a rapid convergence of the lattice model towards
the Bethe-Peierls model for a vanishing lattice period. This establishes for
this system the universality of the zero interaction range limit.Comment: 6 page
SU(3) Quantum Interferometry with single-photon input pulses
We develop a framework for solving the action of a three-channel passive
optical interferometer on single-photon pulse inputs to each channel using
SU(3) group-theoretic methods, which can be readily generalized to higher-order
photon-coincidence experiments. We show that features of the coincidence plots
vs relative time delays of photons yield information about permanents,
immanants, and determinants of the interferometer SU(3) matrix
Checklist of spiders in Tasek Bera Ramsar Site, Pahang, Malaysia
Established since 1995, Tasek Bera is a wetland of international importance. It comprises an area of 31,120 hectares. It is the largest natural freshwater lake in Malaysia. The natural freshwater lake is rich in local flora and fauna. A study of the biodiversity of spider was carried out during the Biodiversity Inventory Program at Tasek Bera Ramsar Site, Pahang from 20th to 26th May 2009.
Throughout the program a total of 216 spiders were collected. Among them, 13 families of spider, namely the Agelenidae, Araneidae, Lycosidae, Nephilidae, Oxyopidae, Pholcidae, Pisauridae, Psechridae, Salticidae, Sparassidae, Tetragnathidae, Theridiidae, and Thomisidae were recorded. Most spiders found on web built between branches are the members of Araneidae, Nephilidae, Psechridae, Tetragnathidae, and Theridiidae while others were either foraging on trees (Oxyopidae, Pholcidae, Pisauridae, and Salticidae) or on the ground (Agelenidae, Lycosidae, and Sparassidae). A high variety of spider species were recorded
Predictable Disruption Tolerant Networks and Delivery Guarantees
This article studies disruption tolerant networks (DTNs) where each node
knows the probabilistic distribution of contacts with other nodes. It proposes
a framework that allows one to formalize the behaviour of such a network. It
generalizes extreme cases that have been studied before where (a) either nodes
only know their contact frequency with each other or (b) they have a perfect
knowledge of who meets who and when. This paper then gives an example of how
this framework can be used; it shows how one can find a packet forwarding
algorithm optimized to meet the 'delay/bandwidth consumption' trade-off:
packets are duplicated so as to (statistically) guarantee a given delay or
delivery probability, but not too much so as to reduce the bandwidth, energy,
and memory consumption.Comment: 9 page
The Fermi level effect in III-V intermixing: The final nail in the coffin?
Copyright 1997 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Journal of Applied Physics 81, 2179 (1997) and may be found at
Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal
Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including pyruvate, oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid plays a central role in the aqueous oxidation of methylglyoxal and it is a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid (20 μM–10 mM) was oxidized by OH radicals, and pyruvic acid and methylglyoxal experimental samples were analyzed using new analytical methods, in order to better understand the formation of SOA from acetic acid and methylglyoxal. Glyoxylic, glycolic, and oxalic acids formed from acetic acid and OH radicals. In contrast to the aqueous OH radical oxidation of methylglyoxal, the aqueous OH radical oxidation of acetic acid did not produce succinic acid and oligomers. This suggests that the methylgloxal-derived oligomers do not form through the acid catalyzed esterification pathway proposed previously. Using results from these experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols
Quantum Transport in Molecular Rings and Chains
We study charge transport driven by deformations in molecular rings and
chains. Level crossings and the associated Longuet-Higgins phase play a central
role in this theory. In molecular rings a vanishing cycle of shears pinching a
gap closure leads, generically, to diverging charge transport around the ring.
We call such behavior homeopathic. In an infinite chain such a cycle leads to
integral charge transport which is independent of the strength of deformation.
In the Jahn-Teller model of a planar molecular ring there is a distinguished
cycle in the space of uniform shears which keeps the molecule in its manifold
of ground states and pinches level crossing. The charge transport in this cycle
gives information on the derivative of the hopping amplitudes.Comment: Final version. 26 pages, 8 fig
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