1,968 research outputs found
Design, development, and fabrication of a functional adhesive bonding repair experiment to be performed during space flight Final report, Nov. 1966 - May 1968
Adhesive repair system for application in weightless vacuum space environmen
A novel scheme to aid coherent detection of GMSK signals in fast Rayleigh fading channels
A novel scheme to insert carrier pilot to Gaussian Minimum Shift Keying (GMSK) signal using Binary Block Code (BBC) and a highpass filter in baseband is proposed. This allows the signal to be coherently demodulated even in a fast Rayleigh fading environment. As an illustrative example, the scheme is applied to a 16 kb/s GMSK signal, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. This modem's 'irreducible error rate' is found to be Pe = 5.5 x 10(exp -5) which is more than that of differential detection. The modem's performance in Rician fading channel is currently under investigation
Commissioning, Performance, and Effect of the Quench Current-boosting Device on a Dedicated Superconducting Magnet
Superconducting magnet training is one of the accelerator related issues
attracting attention due to significant operational costs and time budget
associated to it. It is especially worrisome that magnets based on the
next-generation Nb3Sn technology are affected by long training. While various
efforts are underway to better understand and resolve the problem a parallel
path could also be investigated, a path bypassing the issue. Following the
concept of fast induced over-current during magnet powering, FNAL has developed
an upgradable capacitor-based device to discharge through a superconducting
magnet at quench detection or operator chosen time. The 0.4 F/1 kV device has
been tested on a 1-m-long dipole-coil in a mirror magnet configuration and
conclusive results on magnet training elimination have been observed. In this
paper we discuss the main characteristics of the device, compare simulated
response and actual performance, elaborate on test drivers and outcomes. Next
steps and perspectives for future use are debated
Spin resonance of 2D electrons in a large-area silicon MOSFET
We report electron spin resonance (ESR) measurements on a large-area silicon
MOSFET. An ESR signal at g-factor 1.9999(1), and with a linewidth of 0.6 G, is
observed and found to arise from two-dimensional (2D) electrons at the Si/SiO2
interface. The signal and its intensity show a pronounced dependence on applied
gate voltage. At gate voltages below the threshold of the MOSFET, the signal is
from weakly confined, isolated electrons as evidenced by the Curie-like
temperature dependence of its intensity. The situation above threshold appears
more complicated. These large-area MOSFETs provide the capability to
controllably tune from insulating to conducting regimes by adjusting the gate
voltage while monitoring the state of the 2D electron spins spectroscopically.Comment: 7 pages, 3 figures, submitted to Physica E special edition for
EPS2DS-1
Effect of external magnetic field on electron spin dephasing induced by hyperfine interaction in quantum dots
We investigate the influence of an external magnetic field on spin phase
relaxation of single electrons in semiconductor quantum dots induced by the
hyperfine interaction. The basic decay mechanism is attributed to the
dispersion of local effective nuclear fields over the ensemble of quantum dots.
The characteristics of electron spin dephasing is analyzed by taking an average
over the nuclear spin distribution. We find that the dephasing rate can be
estimated as a spin precession frequency caused primarily by the mean value of
the local nuclear magnetic field. Furthermore, it is shown that the hyperfine
interaction does not fully depolarize electron spin. The loss of initial spin
polarization during the dephasing process depends strongly on the external
magnetic field, leading to the possibility of effective suppression of this
mechanism.Comment: 10 pages, 2 figure
Dynamical supersymmetry of spin particle-magnetic field interaction
We study the super and dynamical symmetries of a fermion in a monopole
background. The Hamiltonian also involves an additional spin-orbit coupling
term, which is parameterized by the gyromagnetic ratio. We construct the
superinvariants associated with the system using a SUSY extension of a
previously proposed algorithm, based on Grassmann-valued Killing tensors.
Conserved quantities arise for certain definite values of the gyromagnetic
factor: SUSY requires ; a Kepler-type dynamical symmetry only
arises, however, for the anomalous values and . The two anomalous
systems can be unified into an SUSY system built by doubling the number
of Grassmann variables. The planar system also exhibits an supersymmetry
without Grassmann variable doubling.Comment: 23 page
Application of Distributed Fiber Optic Strain Sensors to LMQXFA Cold Mass Welding
The future High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at
CERN will include the low-beta inner triplets (Q1, Q2a/b, Q3) for two LHC
insertion regions. The Q1, Q3 components consist of eight 10 m-long LMQXFA
cryo-assemblies fabricated by the HL-LHC Accelerator Upgrade Project. Each
LMQXFA Cold mass contains two Nb3Sn magnets connected in series. A
stainless-steel shell is welded around the two magnets before the insertion
into the cryostat. There is a limit on how much coil preload increase induced
by the shell welding is allowed. Distributed Rayleigh backscattering fiber
optics sensors were used for the first time to obtain a strain map over a wide
area of a Nb3Sn magnet cold mass shell. Data were collected during welding of
the first LMQXFA cold mass and the results confirm that the increase of the
coil pole azimuthal pre-stress after welding do not exceed requirements
Two-spin measurements in exchange interaction quantum computers
We propose and analyze a method for single shot measurement of the total spin of a two electron system in a coupled quantum dot or donor impurity structure, which can be used for readout in a quantum computer. The spin can be inferred by observing spin-dependent fluctuations of charge between the two sites, via a nearby electrometer. Realistic experimental parameters indicate that the fidelity of the measurement can be larger than 0.999 with existing or near-future technology. We also describe how our scheme can be used to implement various one- and two-qubit measurements, and hence to implement universal quantum computation
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