2,966 research outputs found
Status Updates Over Unreliable Multiaccess Channels
Applications like environmental sensing, and health and activity sensing, are
supported by networks of devices (nodes) that send periodic packet
transmissions over the wireless channel to a sink node. We look at simple
abstractions that capture the following commonalities of such networks (a) the
nodes send periodically sensed information that is temporal and must be
delivered in a timely manner, (b) they share a multiple access channel and (c)
channels between the nodes and the sink are unreliable (packets may be received
in error) and differ in quality.
We consider scheduled access and slotted ALOHA-like random access. Under
scheduled access, nodes take turns and get feedback on whether a transmitted
packet was received successfully by the sink. During its turn, a node may
transmit more than once to counter channel uncertainty. For slotted ALOHA-like
access, each node attempts transmission in every slot with a certain
probability. For these access mechanisms we derive the age of information
(AoI), which is a timeliness metric, and arrive at conditions that optimize AoI
at the sink. We also analyze the case of symmetric updating, in which updates
from different nodes must have the same AoI. We show that ALOHA-like access,
while simple, leads to AoI that is worse by a factor of about 2e, in comparison
to scheduled access
Logarithmic correction to the Bekenstein-Hawking entropy of the BTZ black hole
We derive an exact expression for the partition function of the Euclidean BTZ
black hole. Using this, we show that for a black hole with large horizon area,
the correction to the Bekenstein-Hawking entropy is , in
agreement with that for the Schwarzschild black hole obtained in the canonical
gravity formalism and also in a Lorentzian computation of BTZ black hole
entropy. We find that the right expression for the logarithmic correction in
the context of the BTZ black hole comes from the modular invariance associated
with the toral boundary of the black hole.Comment: LaTeX, 10 pages, typos corrected, clarifications adde
Segregation by membrane rigidity in flowing binary suspensions of elastic capsules
Spatial segregation in the wall normal direction is investigated in
suspensions containing a binary mixture of Neo-Hookean capsules subjected to
pressure driven flow in a planar slit. The two components of the binary mixture
have unequal membrane rigidities. The problem is studied numerically using an
accelerated implementation of the boundary integral method. The effect of a
variety of parameters was investigated, including the capillary number,
rigidity ratio between the two species, volume fraction, confinement ratio, and
the number fraction of the more floppy particle in the mixture. It was
observed that in suspensions of pure species, the mean wall normal positions of
the stiff and the floppy particles are comparable. In mixtures, however, the
stiff particles were found to be increasingly displaced towards the walls with
increasing , while the floppy particles were found to increasingly
accumulate near the centerline with decreasing . The origins of this
segregation is traced to the effect of the number fraction on the
localization of the stiff and the floppy particles in the near wall region --
the probability of escape of a stiff particle from the near wall region to the
interior is greatly reduced with increasing , while the exact opposite
trend is observed for a floppy particle with decreasing . Simple model
studies on heterogeneous pair collisions involving a stiff and a floppy
particle mechanistically explain this observation. The key result in these
studies is that the stiff particle experiences much larger cross-stream
displacement in heterogeneous collisions than the floppy particle. A unified
mechanism incorporating the wall-induced migration of deformable particles and
the particle fluxes associated with heterogeneous and homogeneous pair
collisions is presented.Comment: 19 Pages, 16 Figure
Spacetime Dependent Lagrangians and Weak-Strong Duality : Sine Gordon and Massive Thirring Models
The formalism of spacetime dependent lagrangians developed in Ref.1 is
applied to the Sine Gordon and massive Thirring models.It is shown that the
well-known equivalence of these models (in the context of weak-strong duality)
can be understood in this approach from the same considerations as described in
[1] for electromagnetic duality. A further new result is that all these can be
naturally linked to the fact that the holographic principle has analogues at
length scales much larger than quantum gravity. There is also the possibility
of {\it noncommuting coodinates} residing on the boundaries. PACS: 11.15.-q:
11.10/EfComment: Latex, 16 pages, article shortened, references added, minor typos
correcte
Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Cd(II) & UO2(II) Chelates of Schiff Bases Derived from o-Aminobenzenesulphonic Acid & 2-Aminoethanesulphonic Acid & 2-Hydroxy-1-naphthaldehyde
61-6
Black Hole Entropy from a Highly Excited Elementary String
Suggested correspondence between a black hole and a highly excited elementary
string is explored. Black hole entropy is calculated by computing the density
of states for an open excited string. We identify the square root of oscillator
number of the excited string with Rindler energy of black hole to obtain an
entropy formula which, not only agrees at the leading order with the
Bekenstein-Hawking entropy, but also reproduces the logarithmic correction
obtained for black hole entropy in the quantum geometry framework. This
provides an additional supporting evidence for correspondence between black
holes and strings.Comment: revtex, 4 page
First-Order Superfluid to Valence-Bond Solid Phase Transitions in Easy-Plane SU(\u3cem\u3eN\u3c/em\u3e) Magnets for Small \u3cem\u3eN\u3c/em\u3e
We consider the easy-plane limit of bipartite SU(N) Heisenberg Hamiltonians, which have a fundamental representation on one sublattice and the conjugate to fundamental on the other sublattice. For N = 2 the easy plane limit of the SU(2) Heisenberg model is the well-known quantum XY model of a lattice superfluid. We introduce a logical method to generalize the quantum XY model to arbitrary N, which keeps the Hamiltonian sign-free. We show that these quantum Hamiltonians have a world-line representation as the statistical mechanics of certain tightly packed loop models of N colors in which neighboring loops are disallowed from having the same color. In this loop representation we design an efficient Monte Carlo cluster algorithm for our model. We present extensive numerical results for these models on the two dimensional square lattice, where we find the nearest neighbor model has superfluid order for N ≤ 5 and valence-bond order for N \u3e 5. By introducing SU(N) easy-plane symmetric four-spin couplings we are able to tune across the superfluid-VBS phase boundary for all N ≤ 5. We present clear evidence that this quantum phase transition is first order for N = 2 and N = 5, suggesting that easy-plane deconfined criticality runs away generically to a first-order transition for small N
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