Optimal rectification in the ultrastrong coupling regime.

We study the effect of ultrastrong coupling on the transport of heat. In particular, we present a condition for optimal rectification, i.e., flow of heat in one direction and complete isolation in the opposite direction. We show that the strong-coupling formalism is necessary for correctly describing heat flow in a wide range of parameters, including moderate to low couplings. We present a situation in which the strong-coupling formalism predicts optimal rectification whereas the phenomenological approach predicts no heat flow in any direction, for the same parameter values.

Energy transfer dynamics and thermalization of two oscillators interacting via chaos.

We consider the classical dynamics of two particles moving in harmonic potential wells and interacting with the same external environment HE, consisting of N noninteracting chaotic systems. The parameters are set so that when either particle is separately placed in contact with the environment, a dissipative behavior is observed. When both particles are simultaneously in contact with HE an indirect coupling between them is observed only if the particles are in near-resonance. We study the equilibrium properties of the system considering ensemble averages for the case N=1 and single trajectory dynamics for N large. In both cases, the particles and the environment reach an equilibrium configuration at long times, but only for large N can a temperature be assigned to the system.

Energy dissipation via coupling with a finite chaotic environment.

We study the flow of energy between a harmonic oscillator (HO) and an external environment consisting of N two-degrees-of-freedom nonlinear oscillators, ranging from integrable to chaotic according to a control parameter. The coupling between the HO and the environment is bilinear in the coordinates and scales with system size as 1/√N. We study the conditions for energy dissipation and thermalization as a function of N and of the dynamical regime of the nonlinear oscillators. The study is classical and based on a single realization of the dynamics, as opposed to ensemble averages over many realizations. We find that dissipation occurs in the chaotic regime for fairly small values of N, leading to the thermalization of the HO and the environment in a Boltzmann distribution of energies for a well-defined temperature. We develop a simple analytical treatment, based on the linear response theory, that justifies the coupling scaling and reproduces the numerical simulations when the environment is in the chaotic regime.

[Acute toxicity of ammonia in the production process of postlarvae of Penaeus paulensis Pérez-Farfante, 1967]. / Toxicidade aguda da amônia no processo produtivo de pós-larvas de Penaeus paulensis Pérez-Farfante, 1967.

Larval shrimp Penaeus paulensis showed a tendency to decrease in ammonia tolerance as the larva metamorphosed from nauplius to postlarvae stage. The 24-h LC50 were 4.04, 1.70, 2.72, and 1.42 mg/l NH3-N on nauplii, zoea, mysis and postlarvae, respectively. The zoea stage and the initial postlarvae substages were very susceptible to ammonia. The 96-h LC50 values on zoea and postlarvae were 0.69 mg/l and 0.32 mg/l, against 0.80 mg/l NH3-N on mysis. The eggs of Penaeus paulensis were very affected by ammonia, which provoked a progressive decrease in the hatching rate and induced morphological deformities in hatched nauplii. A "safe level" of ammonia was estimated at 0.032 mg/l NH3-N on the basis of 24-h LC50 for eggs.