1,195 research outputs found
AlGaN/GaN HEMT-based fully monolithic X-band low noise amplifier
A fully monolithic AlGaN/GaN HEMT-based low noise amplifier is reported. The circuit demonstrated a noise figure of 3.5 dB, gain of -7.5 dB, input return loss of -7.5 dB, and output return loss of -15 dB at 8.5 GHz. The dc characteristics of individual 0.25-μm × 150-μm transistors were: maximum current density of 1.0 A/mm, maximum transconductance of 170 mS/mm and a threshold voltage of -6.8 V. The devices have a typical short circuit current gain cutoff frequency of 24.5 GHz and a maximum oscillating frequency of 48 GHz. The devices demonstrated a minimum noise figure of 1.6 dB with an associated gain of 10.6 dB at 10 GHz. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Temperature-dependence of a GaN-based HEMT monolithic X-band low noise amplifier
The temperature-dependent performance of a fully monolithic AlGaN/GaN HEMT-based X-band low noise amplifier is reported. The circuit demonstrated a noise figure of 3.5 dB, gain of 7.5 dB, input return loss of -7.5 dB, and output return loss of -15 dB at 8.5 GHz at room temperature. The noise figure at 9.5 GHz increased from 2.5 dB at 43°C to 5.0 dB at 150°C. © 2004 IEEE
Cosmological Evolution of a Purely Conical Codimension-2 Brane World
We study the cosmological evolution of isotropic matter on an infinitely thin
conical codimension-two brane-world. Our analysis is based on the boundary
dynamics of a six-dimensional model in the presence of an induced gravity term
on the brane and a Gauss-Bonnet term in the bulk. With the assumption that the
bulk contains only a cosmological constant Lambda_B, we find that the isotropic
evolution of the brane-universe imposes a tuned relation between the energy
density and the brane equation of state. The evolution of the system has fixed
points (attractors), which correspond to a final state of radiation for
Lambda_B=0 and to de Sitter state for Lambda_B>0. Furthermore, considering
anisotropic matter on the brane, the tuning of the parameters is lifted, and
new regions of the parametric space are available for the cosmological
evolution of the brane-universe. The analysis of the dynamics of the system
shows that, the isotropic fixed points remain attractors of the system, and for
values of Lambda_B which give acceptable cosmological evolution of the equation
of state, the line of isotropic tuning is a very weak attractor. The initial
conditions, in this case, need to be fine tuned to have an evolution with
acceptably small anisotropy.Comment: 20 pages, 4 figures, typo correcte
Quantum entanglement with acousto-optic modulators: 2-photon beatings and Bell experiments with moving beamsplitters
We present an experiment testing quantum correlations with frequency shifted
photons. We test Bell inequality with 2-photon interferometry where we replace
the beamsplitters by acousto-optic modulators, which are equivalent to moving
beamsplitters. We measure the 2-photon beatings induced by the frequency
shifts, and we propose a cryptographic scheme in relation. Finally, setting the
experiment in a relativistic configuration, we demonstrate that the quantum
correlations are not only independent of the distance but also of the time
ordering between the two single-photon measurements.Comment: 14 pages, 16 figure
An interferometric complementarity experiment in a bulk Nuclear Magnetic Resonance ensemble
We have experimentally demonstrated the interferometric complementarity,
which relates the distinguishability quantifying the amount of which-way
(WW) information to the fringe visibility characterizing the wave feature
of a quantum entity, in a bulk ensemble by Nuclear Magnetic Resonance (NMR)
techniques. We primarily concern on the intermediate cases: partial fringe
visibility and incomplete WW information. We propose a quantitative measure of
by an alternative geometric strategy and investigate the relation between
and entanglement. By measuring and independently, it turns out that
the duality relation holds for pure quantum states of the
markers.Comment: 13 page, 5 PS figure
A low-voltage activated, transient calcium current is responsible for the time-dependent depolarizing inward rectification of rat neocortical neurons in vitro
Intracellular recordings were obtained from rat neocortical neurons in vitro. The current-voltage-relationship of the neuronal membrane was investigated using current- and single-electrode-voltage-clamp techniques. Within the potential range up to 25 mV positive to the resting membrane potential (RMP: –75 to –80 mV) the steady state slope resistance increased with depolarization (i.e. steady state inward rectification in depolarizing direction). Replacement of extracellular NaCl with an equimolar amount of choline chloride resulted in the conversion of the steady state inward rectification to an outward rectification, suggesting the presence of a voltage-dependent, persistent sodium current which generated the steady state inward rectification of these neurons. Intracellularly injected outward current pulses with just subthreshold intensities elicited a transient depolarizing potential which invariably triggered the first action potential upon an increase in current strength. Single-electrode-voltage-clamp measurements reveled that this depolarizing potential was produced by a transient calcium current activated at membrane potentials 15–20 mV positive to the RMP and that this current was responsible for the time-dependent increase in the magnitude of the inward rectification in depolarizing direction in rat neocortical neurons. It may be that, together with the persistent sodium current, this calcium current regulates the excitability of these neurons via the adjustment of the action potential threshold
Optical Magnetometry
Some of the most sensitive methods of measuring magnetic fields utilize
interactions of resonant light with atomic vapor. Recent developments in this
vibrant field are improving magnetometers in many traditional areas such as
measurement of geomagnetic anomalies and magnetic fields in space, and are
opening the door to new ones, including, dynamical measurements of bio-magnetic
fields, detection of nuclear magnetic resonance (NMR), magnetic-resonance
imaging (MRI), inertial-rotation sensing, magnetic microscopy with cold atoms,
and tests of fundamental symmetries of Nature.Comment: 11 pages; 4 figures; submitted to Nature Physic
Simulated Annealing for Topological Solitons
The search for solutions of field theories allowing for topological solitons
requires that we find the field configuration with the lowest energy in a given
sector of topological charge. The standard approach is based on the numerical
solution of the static Euler-Lagrange differential equation following from the
field energy. As an alternative, we propose to use a simulated annealing
algorithm to minimize the energy functional directly. We have applied simulated
annealing to several nonlinear classical field theories: the sine-Gordon model
in one dimension, the baby Skyrme model in two dimensions and the nuclear
Skyrme model in three dimensions. We describe in detail the implementation of
the simulated annealing algorithm, present our results and get independent
confirmation of the studies which have used standard minimization techniques.Comment: 31 pages, LaTeX, better quality pics at
http://www.phy.umist.ac.uk/~weidig/Simulated_Annealing/, updated for
publicatio
High-Performance Silicon Photonic Single-Sideband Modulators for Cold Atom Interferometry
The most complicated and challenging system within a light-pulse atom
interferometer (LPAI) is the laser system, which controls the frequencies and
intensities of multiple laser beams over time to configure quantum gravity and
inertial sensors. The main function of an LPAI laser system is to perform
cold-atom generation and state-selective detection and to generate coherent
two-photon process for the light-pulse sequence. Substantial miniaturization
and ruggedization of the laser system can be achieved by bringing together most
key functions of the laser and optical system onto a photonic integrated
circuit (PIC). Here we demonstrate a high-performance silicon photonic
carrier-suppressed single-sideband (CS-SSB) modulator PIC with dual-parallel
Mach-Zehnder modulators (DP-MZMs) operating near 1560 nm, which can dynamically
shift the frequency of the light for the desired function within the LPAI.
Independent RF control of channels in SSB modulator enables the extensive study
of imbalances in both the optical and RF phases and amplitudes to
simultaneously reach 30 dB carrier suppression and unprecedented 47.8 dB
sideband suppression with peak conversion efficiency of -6.846 dB (20.7 %).
Using a silicon photonic SSB modulator with time-multiplexed frequency shifting
in an LPAI laser system, we demonstrate cold-atom generation, state-selective
detection, and the realization of atom interferometer fringes to estimate
gravitational acceleration, , in a
Rubidium (Rb) atom system.Comment: 18 pages, 9 figure
MSLED, Neutrino Oscillations and the Cosmological Constant
We explore the implications for neutrino masses and mixings within the
minimal version of the supersymmetric large-extra-dimensions scenario (MSLED).
This model was proposed in {\tt hep-ph/0404135} to extract the phenomenological
implications of the promising recent attempt (in {\tt hep-th/0304256}) to
address the cosmological constant problem. Remarkably, we find that the
simplest couplings between brane and bulk fermions within this approach can
lead to a phenomenologically-viable pattern of neutrino masses and mixings that
is also consistent with the supernova bounds which are usually the bane of
extra-dimensional neutrino models. Under certain circumstances the MSLED
scenario can lead to a lepton mixing (PMNS) matrix close to the so-called
bi-maximal or the tri-bimaximal forms (which are known to provide a good
description of the neutrino oscillation data). We discuss the implications of
MSLED models for neutrino phenomenology.Comment: 38 pages, 1 figure; Reposted with a few additional reference
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