75,891 research outputs found
Measuring the cosmic proper distance from fast radio bursts
The cosmic proper distance is a fundamental distance in the Universe.
Unlike the luminosity and angular diameter distances, which correspond to the
angular size, the proper distance is the length of light path from the source
to observer. However, the proper distance has not been measured before. The
recent redshift measurement of a repeat fast radio burst (FRB) can shed light
on the proper distance. We show that the proper distance-redshift relation can
indeed be derived from dispersion measures (DMs) of FRBs with measured
redshifts. From Monte Carlo simulations, we find that about 500 FRBs with DM
and redshift measurements can tightly constrain the proper distance-redshift
relation. We also show that the curvature of our Universe can be constrained
with a model-independent method using this derived proper distance-redshift
relation and the observed angular diameter distances. Owing to the high event
rate of FRBs, hundreds of FRBs can be discovered in the future by upcoming
instruments. The proper distance will play an important role in investigating
the accelerating expansion and the geometry of the Universe.Comment: 9 pages, 4 figures, proof versio
Design of a 2.4 GHz High-Performance Up-Conversion Mixer with Current Mirror Topology
In this paper, a low voltage low power up-conversion mixer, designed in a Chartered 0.18 ÎĽm RFCMOS technology, is proposed to realize the transmitter front-end in the frequency band of 2.4 GHz. The up-conversion mixer uses the current mirror topology and current-bleeding technique in both the driver and switching stages with a simple degeneration resistor. The proposed mixer converts an input of 100 MHz intermediate frequency (IF) signal to an output of 2.4 GHz radio frequency (RF) signal, with a local oscillator (LO) power of 2 dBm at 2.3 GHz. A comparison with conventional CMOS up-conversion mixer shows that this mixer has advantages of low voltage, low power consumption and high-performance. The post-layout simulation results demonstrate that at 2.4 GHz, the circuit has a conversion gain of 7.1 dB, an input-referred third-order intercept point (IIP3) of 7.3 dBm and a noise figure of 11.9 dB, while drawing only 3.8 mA for the mixer core under a supply voltage of 1.2 V. The chip area including testing pads is only 0.62Ă—0.65 mm2
Log-Harnack Inequality for Stochastic Differential Equations in Hilbert Spaces and its Consequences
A logarithmic type Harnack inequality is established for the semigroup of
solutions to a stochastic differential equation in Hilbert spaces with
non-additive noise. As applications, the strong Feller property as well as the
entropy-cost inequality for the semigroup are derived with respect to the
corresponding distance (cost function)
Formation of Hydrogenated Graphene Nanoripples by Strain Engineering and Directed Surface Self-assembly
We propose a new class of semiconducting graphene-based nanostructures:
hydrogenated graphene nanoripples (HGNRs), based on continuum-mechanics
analysis and first principles calculations. They are formed via a two-step
combinatorial approach: first by strain engineered pattern formation of
graphene nanoripples, followed by a curvature-directed self-assembly of H
adsorption. It offers a high level of control of the structure and morphology
of the HGNRs, and hence their band gaps which share common features with
graphene nanoribbons. A cycle of H adsorption/desorption at/from the same
surface locations completes a reversible metal-semiconductor-metal transition
with the same band gap.Comment: 11 pages, 5 figure
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