1,341 research outputs found
Extremely high data-rate, reliable network systems research
Significant progress was made over the year in the four focus areas of this research group: gigabit protocols, extensions of metropolitan protocols, parallel protocols, and distributed simulations. Two activities, a network management tool and the Carrier Sensed Multiple Access Collision Detection (CSMA/CD) protocol, have developed to the point that a patent is being applied for in the next year; a tool set for distributed simulation using the language SIMSCRIPT also has commercial potential and is to be further refined. The year's results for each of these areas are summarized and next year's activities are described
Superconducting Order Parameter in Bi-Layer Cuprates: Occurrence of Phase Shifts in Corner Junctions
We study the order parameter symmetry in bi-layer cuprates such as YBaCuO,
where interesting phase shifts have been observed in Josephson junctions.
Taking models which represent the measured spin fluctuation spectra of this
cuprate, as well as more general models of Coulomb correlation effects, we
classify the allowed symmetries and determine their associated physical
properties. phase shifts are shown to be a general consequence of
repulsive interactions, independent of whether a magnetic mechanism is
operative. While it is known to occur in d-states, this behavior can also be
associated with (orthorhombic) s-symmetry when the two sub-band gaps have
opposite phase. Implications for the magnitude of are discussed.Comment: 5 pages, RevTeX 3.0, 9 figures (available upon request
Deterministic mechanical model of T-killer cell polarization reproduces the wandering of aim between simultaneously engaged targets
T-killer cells of the immune system eliminate virus-infected and tumorous cells through direct cell-cell interactions. Reorientation of the killing apparatus inside the T cell to the T-cell interface with the target cell ensures specificity of the immune response. The killing apparatus can also oscillate next to the cell-cell interface. When two target cells are engaged by the T cell simultaneously, the killing apparatus can oscillate between the two interface areas. This oscillation is one of the most striking examples of cell movements that give the microscopist an unmechanistic impression of the cell's fidgety indecision. We have constructed a three-dimensional, numerical biomechanical model of the molecular-motor-driven microtubule cytoskeleton that positions the killing apparatus. The model demonstrates that the cortical pulling mechanism is indeed capable of orienting the killing apparatus into the functional position under a range of conditions. The model also predicts experimentally testable limitations of this commonly hypothesized mechanism of T-cell polarization. After the reorientation, the numerical solution exhibits complex, multidirectional, multiperiodic, and sustained oscillations in the absence of any external guidance or stochasticity. These computational results demonstrate that the strikingly animate wandering of aim in T-killer cells has a purely mechanical and deterministic explanation. © 2009 Kim, Maly
Coulomb Correlations and Pseudo-gap Effects in a Pre-formed Pair Model for the Cuprates
We extend previous work on pre-formed pair models of superconductivity to
incorporate Coulomb correlation effects. For neutral systems, these models have
provided a useful scheme which interpolates between BCS and Bose Einstein
condensation with increasing coupling and thereby describes some aspects of
pseudo-gap phenomena. However, charge fluctuations (via the plasmon,
) significantly modify the collective modes and therefore the
interpolation behavior. We discuss the resulting behavior of the pseudo-gap and
thermodynamic quantities such as , and as a function of
.Comment: 4 pages RevTeX, 3 ps figures included (Submitted to Physical Review B
August 27, 1996
The pseudogap in underdoped high Tc superconductors in the framework of the Boson Fermion model
The question of whether the pseudogap in high cuprates is related to
super conducting precursor effects or to the existence of extrinsic bosonic
massive excitations is investigated on the basis of the Boson-Fermion model.
The characteristic three peak structure of the electronic spectral function and
the temperature dependent Fermi vector derived here are signatures for a two
component scenario which can be tested by ARPES and BIS experiments.Comment: revtex version with 3 eps figures. Revised version to appear in Phys.
Rev. B. 4 c programs adde
Probing superconducting phase fluctuations from the current noise spectrum of pseudogaped metal-superconductor tunnel junctions
We study the current noise spectra of a tunnel junction of a metal with
strong pairing phase fluctuation and a superconductor. It is shown that there
is a characteristic peak in the noise spectrum at the intrinsic Josephson
frequency when is smaller than the pairing gap but
larger than the pairing scattering rate. In the presence of an AC voltage, the
tunnelling current noise shows a series of characteristic peaks with increasing
DC voltage. Experimental observation of these peaks will give direct evidence
of the pair fluctuation in the normal state of high- superconductors and
from the half width of the peaks the pair decay rate can be estimated.Comment: 4 pages, 3 figure
A computationally engineered RAS rheostat reveals RAS-ERK signaling dynamics.
Synthetic protein switches controlled with user-defined inputs are powerful tools for studying and controlling dynamic cellular processes. To date, these approaches have relied primarily on intermolecular regulation. Here we report a computationally guided framework for engineering intramolecular regulation of protein function. We utilize this framework to develop chemically inducible activator of RAS (CIAR), a single-component RAS rheostat that directly activates endogenous RAS in response to a small molecule. Using CIAR, we show that direct RAS activation elicits markedly different RAS-ERK signaling dynamics from growth factor stimulation, and that these dynamics differ among cell types. We also found that the clinically approved RAF inhibitor vemurafenib potently primes cells to respond to direct wild-type RAS activation. These results demonstrate the utility of CIAR for quantitatively interrogating RAS signaling. Finally, we demonstrate the general utility of our approach in design of intramolecularly regulated protein tools by applying it to the Rho family of guanine nucleotide exchange factors
Reduction of Tc due to Impurities in Cuprate Superconductors
In order to explain how impurities affect the unconventional
superconductivity, we study non-magnetic impurity effect on the transition
temperature using on-site U Hubbard model within a fluctuation exchange (FLEX)
approximation. We find that in appearance, the reduction of Tc roughly
coincides with the well-known Abrikosov-Gor'kov formula. This coincidence
results from the cancellation between two effects; one is the reduction of
attractive force due to randomness, and another is the reduction of the damping
rate of quasi-particle arising from electron interaction. As another problem,
we also study impurity effect on underdoped cuprate as the system showing
pseudogap phenomena. To the aim, we adopt the pairing scenario for the
pseudogap and discuss how pseudogap phenomena affect the reduction of Tc by
impurities. We find that 'pseudogap breaking' by impurities plays the essential
role in underdoped cuprate and suppresses the Tc reduction due to the
superconducting (SC) fluctuation.Comment: 14 pages, 28 figures To be published in JPS
Superconducting transitions from the pseudogap state: d-wave symmetry, lattice, and low-dimensional effects
We investigate the behavior of the superconducting transition temperature
within a previously developed BCS-Bose Einstein crossover picture. This
picture, based on a decoupling scheme of Kadanoff and Martin, further extended
by Patton, can be used to derive a simple form for the superconducting
transition temperature in the presence of a pseudogap. We extend previous work
which addressed the case of s-wave pairing in jellium, to explore the solutions
for T_c as a function of variable coupling in more physically relevant
situations. We thereby ascertain the effects of reduced dimensionality,
periodic lattices and a d-wave pairing interaction. Implications for the
cuprate superconductors are discussed.Comment: REVTeX, 11 pages, 6 EPS figures included, Replace with published
versio
Incoherent Pair Tunneling as a Probe of the Cuprate Pseudogap
We argue that incoherent pair tunneling in a cuprate superconductor junction
with an optimally doped superconducting and an underdoped normal lead can be
used to detect the presence of pairing correlations in the pseudogap phase of
the underdoped lead. We estimate that the junction characteristics most
suitable for studying the pair tunneling current are close to recently
manufactured cuprate tunneling devices.Comment: ReVTeX 3.1; 4 pages, 2 EPS figures (included
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