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The beta subunit of the signal recognition particle receptor is a transmembrane GTPase that anchors the alpha subunit, a peripheral membrane GTPase, to the endoplasmic reticulum membrane.
The signal recognition particle receptor (SR) is required for the cotranslational targeting of both secretory and membrane proteins to the endoplasmic reticulum (ER) membrane. During targeting, the SR interacts with the signal recognition particle (SRP) which is bound to the signal sequence of the nascent protein chain. This interaction catalyzes the GTP-dependent transfer of the nascent chain from SRP to the protein translocation apparatus in the ER membrane. The SR is a heterodimeric protein comprised of a 69-kD subunit (SR alpha) and a 30-kD subunit (SR beta) which are associated with the ER membrane in an unknown manner. SR alpha and the 54-kD subunits of SRP (SRP54) each contain related GTPase domains which are required for SR and SRP function. Molecular cloning and sequencing of a cDNA encoding SR beta revealed that SR beta is a transmembrane protein and, like SR alpha and SRP54, is a member of the GTPase superfamily. Although SR beta defines its own GTPase subfamily, it is distantly related to ARF and Sar1. Using UV cross-linking, we confirm that SR beta binds GTP specifically. Proteolytic digestion experiments show that SR alpha is required for the interaction of SRP with SR. SR alpha appears to be peripherally associated with the ER membrane, and we suggest that SR beta, as an integral membrane protein, mediates the membrane association of SR alpha. The discovery of its guanine nucleotide-binding domain, however, makes it likely that its role is more complex than that of a passive anchor for SR alpha. These findings suggest that a cascade of three directly interacting GTPases functions during protein targeting to the ER membrane
Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation
Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the
coherent splitting of Cooper pairs from a superconductor to two spatially
separated quantum dots has been predicted to generate nonlocal pairs of
entangled electrons. In order to test this hypothesis, we propose a scheme to
transfer the spin state of a split Cooper pair onto the polarization state of a
pair of optical photons. We show that the produced photon pairs can be used to
violate a Bell inequality, unambiguously demonstrating the entanglement of the
split Cooper pairs.Comment: 11 pages, 9 figures, v3 with added reference
Transient excitation and data processing techniques employing the fast fourier transform for aeroelastic testing
The development of testing techniques useful in airplane ground resonance testing, wind tunnel aeroelastic model testing, and airplane flight flutter testing is presented. Included is the consideration of impulsive excitation, steady-state sinusoidal excitation, and random and pseudorandom excitation. Reasons for the selection of fast sine sweeps for transient excitation are given. The use of the fast fourier transform dynamic analyzer (HP-5451B) is presented, together with a curve fitting data process in the Laplace domain to experimentally evaluate values of generalized mass, model frequencies, dampings, and mode shapes. The effects of poor signal to noise ratios due to turbulence creating data variance are discussed. Data manipulation techniques used to overcome variance problems are also included. The experience is described that was gained by using these techniques since the early stages of the SST program. Data measured during 747 flight flutter tests, and SST, YC-14, and 727 empennage flutter model tests are included
An ellipsometer with variable angle of incidence for studies in ultrahigh vacuum
The windows for the vacuum chamber are incorporated into the optical bench system by means of flexible bellows which allow measurements to be made over a large range of angle of incidence, one of which is chosen so that maximum sensitivity is obtained. The principal angle of incidence was determined, and straightforward corrections for strain birefringence of vacuum chamber windows were made. Atomically clean surfaces of sodium chloride and lithium fluoride were investigated to verify the performance of the system. Submonolayer and monolayer coverage of water on these surfaces could be detected. On cleavage planes of NaCl, a first monolayer of adsorbed water is complete at about one torr only
Fleming's bound for the decay of mixed states
Fleming's inequality is generalized to the decay function of mixed states. We
show that for any symmetric hamiltonian and for any density operator
on a finite dimensional Hilbert space with the orthogonal projection onto
the range of there holds the estimate \Tr(\Pi \rme^{-\rmi ht}\rho
\rme^{\rmi ht}) \geq\cos^{2}((\Delta h)_{\rho}t) for all real with
We show that equality either holds for all
or it does not hold for a single with All the density operators saturating the bound for
all i.e. the mixed intelligent states, are determined.Comment: 12 page
Stink Bugs (Hemiptera: Heteroptera: Pentatomidae) of Minnesota: An Annotated Checklist and New State Records
Pentatomidae have been relatively poorly documented in Minnesota. Based on literature and museum records, an annotated checklist of the Pentatomidae of Minnesota was created. State-level and county-level records for Minnesota and the distribution of each species in North America are provided. Fifty-one species of Pentatomidae (12 Asopinae, 37 Pentatominae, and 2 Podopinae) are recorded for Minnesota. Of this total, 15 species are newly recorded for the state. Knowledge of the fauna of Pentatomidae in Minnesota will be important for providing baseline data for monitoring of potential shifts in the fauna resulting from the invasions of exotic Pentatomidae. Furthermore, a list of native Pentatomidae will be necessary for monitoring non-target impacts, if classical biological control is implemented for management of exotic Pentatomidae
Quantum Phase Transition in a Multi-Level Dot
We discuss electronic transport through a lateral quantum dot close to the
singlet-triplet degeneracy in the case of a single conduction channel per lead.
By applying the Numerical Renormalization Group, we obtain rigorous results for
the linear conductance and the density of states. A new quantum phase
transition of the Kosterlitz-Thouless type is found, with an exponentially
small energy scale close to the degeneracy point. Below , the
conductance is strongly suppressed, corresponding to a universal dip in the
density of states. This explains recent transport measurements.Comment: 4 pages, 5 eps figures, published versio
Kondo effect in coupled quantum dots with RKKY interaction: Finite temperature and magnetic field effects
We study transport through two quantum dots coupled by an RKKY interaction as
a function of temperature and magnetic field. By applying the Numerical
Renormalization Group (NRG) method we obtain the transmission and the linear
conductance. At zero temperature and magnetic field, we observe a quantum phase
transition between the Kondo screened state and a local spin singlet as the
RKKY interaction is tuned. Above the critical RKKY coupling the Kondo peak is
split. However, we find that both finite temperature and magnetic field restore
the Kondo resonance. Our results agree well with recent transport experiments
on gold grain quantum dots in the presence of magnetic impurities.Comment: 4 pages, 5 figure
Computer Simulation Study of the Phase Behavior and Structural Relaxation in a Gel-Former Modeled by Three Body Interactions
We report a computer simulation study of a model gel-former obtained by
modifying the three-body interactions of the Stillinger-Weber potential for
silicon. This modification reduces the average coordination number and
consequently shifts the liquid-gas phase coexistence curve to low densities,
thus facilitating the formation of gels without phase separation. At low
temperatures and densities, the structure of the system is characterized by the
presence of long linear chains interconnected by a small number of three
coordinated junctions at random locations. At small wave-vectors the static
structure factor shows a non-monotonic dependence on temperature, a behavior
which is due to the competition between the percolation transition of the
particles and the stiffening of the formed chains. We compare in detail the
relaxation dynamics of the system as obtained from molecular dynamics with the
one obtained from Monte Carlo dynamics. We find that the bond correlation
function displays stretched exponential behavior at moderately low temperatures
and densities, but exponential relaxation at low temperatures. The bond
lifetime shows an Arrhenius behavior, independent of the microscopic dynamics.
For the molecular dynamics at low temperatures, the mean squared displacement
and the (coherent and incoherent) intermediate scattering function display at
intermediate times a dynamics with ballistic character and we show that this
leads to compressed exponential relaxation. For the Monte Carlo dynamics we
find always an exponential or stretched exponential relaxation. Thus we
conclude that the compressed exponential relaxation observed in experiments is
due to the out-of-equilibrium dynamics
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