470 research outputs found
On the nature of X-Ray Flashes
We discuss the origin of X-Ray Flashes (XRFs), a recently discovered class of
Gamma-Ray Bursts (GRBs). Using a simplified model for internal shocks we check
if XRFs can be intrinsically soft due to some specific values of the parameters
describing the relativistic outflow emerging from the central engine. We
generate a large number of synthetic events and find that XRFs are obtained
when the contrast Gamma_max/Gamma_min of the Lorentz factor distribution is
small while the average Lorentz factor Gamma is large. A few XRFs may be GRBs
at large redshifts but we exclude this possibility for the bulk of the
population. If outflows with a small contrast are commonly produced, even a
large population of XRFs could be explained. If conversely the Lorentz factor
distribution within the wind is broad, one should then rely on extrinsic
causes, such as viewing angle effects or high redshift.Comment: 9 pages, 8 figures, to appear in A&
The E-peak distribution of the GRBs detected by HETE FREGATE instrument
The FREGATE gamma ray detector of HETE-2 is sensitive to photons between 6
and 400 keV. This sensitivity range, extended towards low energies, allows us
to explore the emission of GRBs in hard X-rays. We fit the spectra of 23 GRBs
with Band's spectral function in order to derive the distribution of their peak
energies (E-peak). This distribution is then compared with the E-peak
distributions measured by BATSE and GINGA.Comment: 3 pages, Woods Hole Proceeding
Charge dynamics and spin blockade in a hybrid double quantum dot in silicon
Electron spin qubits in silicon, whether in quantum dots or in donor atoms,
have long been considered attractive qubits for the implementation of a quantum
computer due to the semiconductor vacuum character of silicon and its
compatibility with the microelectronics industry. While donor electron spins in
silicon provide extremely long coherence times and access to the nuclear spin
via the hyperfine interaction, quantum dots have the complementary advantages
of fast electrical operations, tunability and scalability. Here we present an
approach to a novel hybrid double quantum dot by coupling a donor to a
lithographically patterned artificial atom. Using gate-based rf reflectometry,
we probe the charge stability of this double quantum dot system and the
variation of quantum capacitance at the interdot charge transition. Using
microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterise
the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time
T1 of 100 ns. Additionally, we demonstrate spin blockade at the inderdot
transition, opening up the possibility to operate this coupled system as a
singlet-triplet qubit or to transfer a coherent spin state between the quantum
dot and the donor electron and nucleus.Comment: 6 pages, 4 figures, supplementary information (3 pages, 4 figures
Ultra-High-density 3D vertical RRAM with stacked JunctionLess nanowires for In-Memory-Computing applications
The Von-Neumann bottleneck is a clear limitation for data-intensive
applications, bringing in-memory computing (IMC) solutions to the fore. Since
large data sets are usually stored in nonvolatile memory (NVM), various
solutions have been proposed based on emerging memories, such as OxRAM, that
rely mainly on area hungry, one transistor (1T) one OxRAM (1R) bit-cell. To
tackle this area issue, while keeping the programming control provided by 1T1R
bit-cell, we propose to combine gate-all-around stacked junctionless nanowires
(1JL) and OxRAM (1R) technology to create a 3-D memory pillar with ultrahigh
density. Nanowire junctionless transistors have been fabricated, characterized,
and simulated to define current conditions for the whole pillar. Finally, based
on Simulation Program with Integrated Circuit Emphasis (SPICE) simulations, we
demonstrated successfully scouting logic operations up to three-pillar layers,
with one operand per layer
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