11,909 research outputs found
Constitutional Law - First Amendment - Establishment Clause - Retroactive Effect
The United States Supreme Court has held that parochial schools\u27 good-faith, reasonable reliance upon an untested state aid program that was subsequently declared unconstitutional as involving excessive entanglement of church and state, justified a district court order that allowed reimbursement for services rendered prior to the program\u27s invalidation.
Lemon v. Kurtzman, 411 U.S. 192 (1973)
Cryo-EM structure of the E. coli translating ribosome in complex with SRP and its receptor
We report the 'early' conformation of the Escherichia coli signal recognition particle (SRP) and its receptor FtsY bound to the translating ribosome, as determined by cryo-EM. FtsY binds to the tetraloop of the SRP RNA, whereas the NG domains of the SRP protein and FtsY interact weakly in this conformation. Our results suggest that optimal positioning of the SRP RNA tetraloop and the Ffh NG domain leads to FtsY recruitment
ALTERNATIVE METHODS OF FORECASTING AGRICULTURAL WATER DEMAND: A CASE STUDY ON THE FLINT RIVER BASIN IN GEORGIA
Future agricultural water demands are determined by employing forecasts from irrigated crop acreage models. Forecasts of prices and yields, and variances and covariances of crop returns are employed for forecasting crop acreage. Results provide insights into the value of rational expectations in forecasting agricultural water demand.Resource /Energy Economics and Policy,
Pulse Control of Decoherence in a Qubit Coupled with a Quantum Environment
We study the time evolution of a qubit linearly coupled with a quantum
environment under a sequence of short pi pulses. Our attention is focused on
the case where qubit-environment interactions induce the decoherence with
population decay. We assume that the environment consists of a set of bosonic
excitations. The time evolution of the reduced density matrix for the qubit is
calculated in the presence of periodic short pi pulses. We confirm that the
decoherence is suppressed if the pulse interval is shorter than the correlation
time for qubit-environment interactions.Comment: 5 pages, 2figure
SPORT: A new sub-nanosecond time-resolved instrument to study swift heavy ion-beam induced luminescence - Application to luminescence degradation of a fast plastic scintillator
We developed a new sub-nanosecond time-resolved instrument to study the
dynamics of UV-visible luminescence under high stopping power heavy ion
irradiation. We applied our instrument, called SPORT, on a fast plastic
scintillator (BC-400) irradiated with 27-MeV Ar ions having high mean
electronic stopping power of 2.6 MeV/\mu m. As a consequence of increasing
permanent radiation damages with increasing ion fluence, our investigations
reveal a degradation of scintillation intensity together with, thanks to the
time-resolved measurement, a decrease in the decay constant of the
scintillator. This combination indicates that luminescence degradation
processes by both dynamic and static quenching, the latter mechanism being
predominant. Under such high density excitation, the scintillation
deterioration of BC-400 is significantly enhanced compared to that observed in
previous investigations, mainly performed using light ions. The observed
non-linear behaviour implies that the dose at which luminescence starts
deteriorating is not independent on particles' stopping power, thus
illustrating that the radiation hardness of plastic scintillators can be
strongly weakened under high excitation density in heavy ion environments.Comment: 5 figures, accepted in Nucl. Instrum. Methods
Entanglement dynamics of bipartite system in squeezed vacuum reservoirs
Entanglement plays a crucial role in quantum information protocols, thus the
dynamical behavior of entangled states is of a great importance. In this paper
we suggest a useful scheme that permits a direct measure of entanglement in a
two-qubit cavity system. It is realized in the cavity-QED technology utilizing
atoms as fying qubits. To quantify entanglement we use the concurrence. We
derive the conditions, which assure that the state remains entangled in spite
of the interaction with the reservoir. The phenomenon of sudden death
entanglement (ESD) in a bipartite system subjected to squeezed vacuum reservoir
is examined. We show that the sudden death time of the entangled states depends
on the initial preparation of the entangled state and the parameters of the
squeezed vacuum reservoir.Comment: 10 pages, 5 figures, CEWQO17(St Andrews
A Link-Level Simulator of the cdma2000 Reverse-Link Physical Layer.
The cdma2000 system is an evolutionary enhancement of the IS-95 standards which support 3G services defined by the International Telecommunications Union (ITU). cdma2000 comes in two phases: 1XRTT and 3XRTT (1X and 3X indicates the number of 1.25 MHz wide radio carrier channels used and RTT stands for Radio Transmission Technology). The cdma2000 1XRTT, which operates within a 1.25 MHz bandwidth, can be utilized in existing IS-95 CDMA channels as it uses the same bandwidth, while 3XRTT requires the commitment of 5 MHz bandwidth to support higher data rates. This paper describes a software model implementation of the cdma2000 reverse link and its application for evaluating the effect of rake receiver design parameters on the system performance under various multipath fading conditions. The cdma2000 models were developed at the National Institute of Standards and Technology (NIST), using SPW (Signal Processing Worksystem) commercial software tools. The model has been developed in a generic manner that includes all the reverse link six radio configurations and their corresponding data rates, according to cdma2000 specifications. After briefly reviewing the traffic channel characteristics of the cdma2000 reverse link (subscriber to base station), the paper discusses the rake receiver implementation including an ideal rake receiver. It then evaluates the performance of each receiver for a Spreading Rate 3 (3XRTT) operation, which is considered as a true "3G" cdma2000 technology. These evaluations are based on the vehicular IMT-2000 (International Mobile Telecommunication 2000) channel model using the link budget defined in cdma2000 specifications for the reverse link
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
Exploiting Randomness in Quantum Information Processing
We consider how randomness can be made to play a useful role in quantum
information processing - in particular, for decoherence control and the
implementation of quantum algorithms. For a two-level system in which the
decoherence channel is non-dissipative, we show that decoherence suppression is
possible if memory is present in the channel. Random switching between two
potentially harmful noise sources can then provide a source of stochastic
control. Such random switching can also be used in an advantageous way for the
implementation of quantum algorithms.Comment: 10 pages, final versio
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