27,040 research outputs found
A RECONSTRUCTION OF THE GREEK-ROMAN REPEATING CATAPULT
An “automatic” repeating weapon used by the Roman army is presented. Firstly a short description is shown of the working principle of the torsion motor that powered the Greek-Roman catapults. This is followed by the description of the reconstructions of these ancient weapons made by those scientists who studied repeating catapults. The authors then propose their own reconstruction. The latter differs from the previous ones because it proposes a different working cycle that is almost automatic and much safer for the operators. The authors based their reconstruction of the weapon starting from the work of previous scientists and on their own translation of the original text (in ancient Greek) by Philon of Byzantium
N=2 Chern-Simons-Matter Theories Without Vortices
We study Chern-Simons-matter theories with gauge group
. We find that, when , the partition
function computed by localization dramatically simplifies and collapses to a
single term. We show that the same condition prevents the theory from having
supersymmetric vortex configurations. The theories include mass-deformed ABJM
theory with gauge group as a particular case.
Similar features are shared by a class of CS-matter theories with gauge group
.Comment: 17 page
Tuning the electronic transport properties of graphene through functionalisation with fluorine
Engineering the electronic properties of graphene has triggered great
interest for potential applications in electronics and opto-electronics. Here
we demonstrate the possibility to tune the electronic transport properties of
graphene monolayers and multilayers by functionalisation with fluorine. We show
that by adjusting the fluorine content different electronic transport regimes
can be accessed. For monolayer samples, with increasing the fluorine content,
we observe a transition from electronic transport through Mott variable range
hopping in two dimensions to Efros - Shklovskii variable range hopping.
Multilayer fluorinated graphene with high concentration of fluorine show
two-dimensional Mott variable range hopping transport, whereas CF0.28
multilayer flakes have a band gap of 0.25eV and exhibit thermally activated
transport. Our experimental findings demonstrate that the ability to control
the degree of functionalisation of graphene is instrumental to engineer
different electronic properties in graphene materials.Comment: 6 pages, 5 figure
Double-gated graphene-based devices
We discuss transport through double gated single and few layer graphene
devices. This kind of device configuration has been used to investigate the
modulation of the energy band structure through the application of an external
perpendicular electric field, a unique property of few layer graphene systems.
Here we discuss technological details that are important for the fabrication of
top gated structures, based on electron-gun evaporation of SiO. We perform
a statistical study that demonstrates how --contrary to expectations-- the
breakdown field of electron-gun evaporated thin SiO films is comparable to
that of thermally grown oxide layers. We find that a high breakdown field can
be achieved in evaporated SiO only if the oxide deposition is directly
followed by the metallization of the top electrodes, without exposure to air of
the SiO layer.Comment: Replaced with revised version. To appear on New Journal of Physic
Direct observation of a gate tunable band-gap in electrical transport in ABC-trilayer graphene
Few layer graphene systems such as Bernal stacked bilayer and rhombohedral
(ABC-) stacked trilayer offer the unique possibility to open an electric field
tunable energy gap. To date, this energy gap has been experimentally confirmed
in optical spectroscopy. Here we report the first direct observation of the
electric field tunable energy gap in electronic transport experiments on doubly
gated suspended ABC-trilayer graphene. From a systematic study of the
non-linearities in current \textit{versus} voltage characteristics and the
temperature dependence of the conductivity we demonstrate that thermally
activated transport over the energy-gap dominates the electrical response of
these transistors. The estimated values for energy gap from the temperature
dependence and from the current voltage characteristics follow the
theoretically expected electric field dependence with critical exponent .
These experiments indicate that high quality few-layer graphene are suitable
candidates for exploring novel tunable THz light sources and detectors.Comment: Nano Letters, 2015 just accepted, DOI: 10.1021/acs.nanolett.5b0077
Lowest order Virtual Element approximation of magnetostatic problems
We give here a simplified presentation of the lowest order Serendipity
Virtual Element method, and show its use for the numerical solution of linear
magneto-static problems in three dimensions. The method can be applied to very
general decompositions of the computational domain (as is natural for Virtual
Element Methods) and uses as unknowns the (constant) tangential component of
the magnetic field on each edge, and the vertex values of the
Lagrange multiplier (used to enforce the solenoidality of the magnetic
induction ). In this respect the method can be seen
as the natural generalization of the lowest order Edge Finite Element Method
(the so-called "first kind N\'ed\'elec" elements) to polyhedra of almost
arbitrary shape, and as we show on some numerical examples it exhibits very
good accuracy (for being a lowest order element) and excellent robustness with
respect to distortions
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