No abstract

Strong inter-particle interactions between polaritons have traditionally stemmed from their exciton component. In this work, we impart a strong photonic nonlinearity to a polaritonic mode by embedding a nonlinear polymethine dye within a high-Q all-metal microcavity. We demonstrate nonlinear microcavities operating in the ultrastrong coupling regime with a normalized coupling ratio of 62%, the highest reported to date. When pumping the lower polariton branch, we observe tunable third-harmonic generation spanning the entire visible spectrum, with internal conversion enhancements more than three orders of magnitude larger than in bare films. Transfer matrix calculations indicate that the observed enhancements are consistent with the enhanced pump electric field.

No abstract

No abstract

Vehicular Ad Hoc Networks (VANETs) are attracting the attention of researchers, industry, and governments for their potential of significantly increasing the safety level on the road. In order to understand whether VANETs can actually realize this goal, in this paper we analyze the dynamics of multi-hop emergency message dissemination in VANETs. Under a probabilistic wireless channel model that accounts for interference, we derive lower bounds on the probability that a car at distance d from the source of the emergency message correctly receives the message within time t. Besides d and t, this probability depends also on 1-hop channel reliability, which we model as a probability value p, and on the message dissemination strategy. Our bounds are derived for an idealized dissemination strategy which ignores interference, and for two provably near-optimal dissemination strategies under protocol interference. The bounds derived in the first part of the paper are used to carefully analyze the tradeoff between the safety level on the road (modeled by parameters d and t), and the value of 1-hop message reliability p. The analysis of this tradeoff discloses several interesting insights that can be very useful in the design of practical emergency message dissemination strategies.

No abstract

We examine the following question: 'Given a problem, is it more difficult to tell how many solutions the problem has than just deciding whether it has a solution?'. We show, that in specific cases, the question can be put into a mathematically meaningful form, namely when we can translate 'number of solutions' as 'number of distinct accepting computations of a nondeterministic Turing machine' (perhaps with appropriate weights). In this context, as we show, these questions are equivalent to problems about probabilistic machines (in the sense ofGill (9)).In the first part of the paper we examine time-bounded computations, and justify our claim that this formalization is really the ma thematical form of the question above by exhibiting a unifying model (the treshold machine) which has a special subcases the nondeterministic and the probabilistic machines. We show that natural complete problems exist and prove some elementary properties of the model.In the second part we examine tape-bounded machines. We show that probabilistic tape-bounded machines may be simulated by determin- and is quite involved, using some powerful recent results in complexity theory (i0) (18) (4). i.i. INTRODUCTIONA central question in the theory of computational complexity

No abstract