504 research outputs found
Transformations among Pure Multipartite Entangled States via Local Operations Are Almost Never Possible
Local operations assisted by classical communication (LOCC) constitute the
free operations in entanglement theory. Hence, the determination of LOCC
transformations is crucial for the understanding of entanglement. We
characterize here almost all LOCC transformations among pure multipartite
multilevel states. Combined with the analogous results for qubit states shown
by Gour \emph{et al.} [J. Math. Phys. 58, 092204 (2017)], this gives a
characterization of almost all local transformations among multipartite pure
states. We show that nontrivial LOCC transformations among generic, fully
entangled, pure states are almost never possible. Thus, almost all multipartite
states are isolated. They can neither be deterministically obtained from
local-unitary-inequivalent (LU-inequivalent) states via local operations, nor
can they be deterministically transformed to pure, fully entangled
LU-inequivalent states. In order to derive this result, we prove a more general
statement, namely, that, generically, a state possesses no nontrivial local
symmetry. We discuss further consequences of this result for the
characterization of optimal, probabilistic single copy and probabilistic
multi-copy LOCC transformations and the characterization of LU-equivalence
classes of multipartite pure states.Comment: 13 pages main text + 10 pages appendix, 1 figure; close to published
versio
Phosphorylation and Dephosphorylation of the RIG-I-like Receptors: A Safety Latch on a Fateful Pathway
Activation of antiviral responses by RNA sensors RIG-I and MDA5 must be stringently controlled. In this issue of Immunity, Wies et al. (2013) show that a requirement for activation-induced dephosphorylation of these proteins reinforces this restriction
The Mason Test: A Defense Against Sybil Attacks in Wireless Networks Without Trusted Authorities
Wireless networks are vulnerable to Sybil attacks, in which a malicious node
poses as many identities in order to gain disproportionate influence. Many
defenses based on spatial variability of wireless channels exist, but depend
either on detailed, multi-tap channel estimation - something not exposed on
commodity 802.11 devices - or valid RSSI observations from multiple trusted
sources, e.g., corporate access points - something not directly available in ad
hoc and delay-tolerant networks with potentially malicious neighbors. We extend
these techniques to be practical for wireless ad hoc networks of commodity
802.11 devices. Specifically, we propose two efficient methods for separating
the valid RSSI observations of behaving nodes from those falsified by malicious
participants. Further, we note that prior signalprint methods are easily
defeated by mobile attackers and develop an appropriate challenge-response
defense. Finally, we present the Mason test, the first implementation of these
techniques for ad hoc and delay-tolerant networks of commodity 802.11 devices.
We illustrate its performance in several real-world scenarios
Language Without Words: A Pointillist Model for Natural Language Processing
This paper explores two separate questions: Can we perform natural language
processing tasks without a lexicon?; and, Should we? Existing natural language
processing techniques are either based on words as units or use units such as
grams only for basic classification tasks. How close can a machine come to
reasoning about the meanings of words and phrases in a corpus without using any
lexicon, based only on grams?
Our own motivation for posing this question is based on our efforts to find
popular trends in words and phrases from online Chinese social media. This form
of written Chinese uses so many neologisms, creative character placements, and
combinations of writing systems that it has been dubbed the "Martian Language."
Readers must often use visual queues, audible queues from reading out loud, and
their knowledge and understanding of current events to understand a post. For
analysis of popular trends, the specific problem is that it is difficult to
build a lexicon when the invention of new ways to refer to a word or concept is
easy and common. For natural language processing in general, we argue in this
paper that new uses of language in social media will challenge machines'
abilities to operate with words as the basic unit of understanding, not only in
Chinese but potentially in other languages.Comment: 5 pages, 2 figure
Translation of mRNA for human lymphotoxin in microinjected Xenopus oocytes
AbstractSynthesis and secretion of biologically active human lymphotoxin (LT) can be detected in Xenopus laevis oocytes following their inoculation with poly(A+) RNA from human stimulated peripheral blood lymphocytes, but not in oocytes inoculated with RNA from unstimulated lymphocytes or from fibroblastoid cells. In size-fractionating mRNA of stimulated lymphocytes most LT activity is found to be coded for by RNA with an approximate sedimentation value of 19 S
- …