9,005 research outputs found
Modulator for tone and binary signals
Tones and binary information are transmitted as phase variations on a carrier wave of constant amplitude and frequency. The carrier and tones are applied to a balanced modulator for deriving an output signal including a pair of sidebands relative to the carrier. The carrier is phase modulated by a digital signal so that it is + or - 90 deg out of phase with the predetermined phase of the carrier. The carrier is combined in an algebraic summing device with the phase modulated signal and the balanced modulator output signal. The output of the algebraic summing device is hard limited to derive a constant amplitude and frequency signal having very narrow bandwidth requirements. At a receiver, the tones and binary data are detected with a phase locked loop having a voltage controlled oscillator driving a pair of orthogonal detection channels
Theory of the Jamming Transition at Finite Temperature
A theory for the microscopic structure and the vibrational properties of soft
sphere glass at finite temperature is presented. With an effective potential,
derived here, the phase diagram and vibrational properties are worked out
around the Maxwell critical point at zero temperature and pressure .
Variational arguments and effective medium theory identically predict a
non-trivial temperature scale with
such that low-energy vibrational properties are hard-sphere like for , and zero-temperature soft-sphere like otherwise. However, due to
crossovers in the equation of state relating , , and the packing fraction
, these two regimes lead to four regions where scaling behaviors differ
when expressed in terms of and . Scaling predictions are presented
for the mean-squared displacement, characteristic frequency, shear modulus, and
characteristic elastic length in all regions of the phase diagram.Comment: 8 pages + 3 pages S
Asymptotically simple spacetime manifolds
This is the published version, also available here: http://dx.doi.org/10.1063/1.1666825.Asymptotic simplicity is shown to be kâstable (kâ„3) at any Minkowski metric on R4 in both the Whitney fine Ck topology and a coarser topology (in which the Ck twiceâconvariant symmetric tensors form a Banach manifold whose connected components consist of tensor field asymptotic to one another at null infinity). This result, together with a sequential method for solving the field equations previously proposed by the authors, allows a fairly straightforward proof that a wellâknown result in the linearized theory holds in the full nonlinear theory as well: There are no nontrivial (i.e., nonâMinkowskian) asymptotically simple vacuum metrics on R4 whose conformal curvature tensors result from prescribing zero initial data on past null infinity
Weak gravitational fields
This is the published version, also available here: http://dx.doi.org/10.1063/1.1666824.We consider the set of Ck bounded tensor fields of type (r,s) on R 4 in the topology of uniform Ck convergence. For each kâ„2, the map sending a metric to its curvature tensor is shown to be analytic at the Minkowski metric. The same is true of the map sending a metric to its Einstein tensor. The wellâknown linearized theory of gravitation amounts to studying the directional derivatives of these maps. An iterative method for solving the full field equations along an analytic curve of Einstein tensors passing through zero is proposed
MoodBar: Increasing new user retention in Wikipedia through lightweight socialization
Socialization in online communities allows existing members to welcome and
recruit newcomers, introduce them to community norms and practices, and sustain
their early participation. However, socializing newcomers does not come for
free: in large communities, socialization can result in a significant workload
for mentors and is hard to scale. In this study we present results from an
experiment that measured the effect of a lightweight socialization tool on the
activity and retention of newly registered users attempting to edit for the
first time Wikipedia. Wikipedia is struggling with the retention of newcomers
and our results indicate that a mechanism to elicit lightweight feedback and to
provide early mentoring to newcomers improves their chances of becoming
long-term contributors.Comment: 9 pages, 5 figures, accepted for presentation at CSCW'1
Boundedness of Pseudodifferential Operators on Banach Function Spaces
We show that if the Hardy-Littlewood maximal operator is bounded on a
separable Banach function space and on its associate space
, then a pseudodifferential operator
is bounded on whenever the symbol belongs to the
H\"ormander class with ,
or to the the Miyachi class
with ,
. This result is applied to the case of
variable Lebesgue spaces .Comment: To appear in a special volume of Operator Theory: Advances and
Applications dedicated to Ant\'onio Ferreira dos Santo
Shwartzman reaction after human renal homotransplantation.
In three human recipients, five renal homografts were destroyed within a few minutes to hours after their revascularization in the new host. The kidneys, removed one to 54 days later, had cortical necrosis. The major vessels were patent, but the arterioles and glomeruli were the site of fibrin deposition. There was little or no fixation of host immunoglobulins in the homografts. The findings were characteristic of a generalized Shwartzman reaction. Although the cause (or causes) of the Shwartzman reaction in our patients is not known, they may have been conditioned by the bacterial contamination and hemolysis that often attend hemodialysis, by immunosuppression and by the transplantation itself. Some of the patients have preformed lymphocytotoxic antibodies. Thus, certain patients may be predisposed. High-risk patients should be recognized and treated prophylactically with anticoagulants
Asymptotically exact probability distribution for the Sinai model with finite drift
We obtain the exact asymptotic result for the disorder-averaged probability
distribution function for a random walk in a biased Sinai model and show that
it is characterized by a creeping behavior of the displacement moments with
time, ~ t^{\mu n} where \mu is dimensionless mean drift. We employ a
method originated in quantum diffusion which is based on the exact mapping of
the problem to an imaginary-time Schr\"{odinger} equation. For nonzero drift
such an equation has an isolated lowest eigenvalue separated by a gap from
quasi-continuous excited states, and the eigenstate corresponding to the former
governs the long-time asymptotic behavior.Comment: 4 pages, 2 figure
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