Kinetics of Recovery of the Dark-adapted Salamander Rod Photoresponse

The kinetics of the dark-adapted salamander rod photocurrent response to flashes producing from 10 to 105 photoisomerizations (Φ) were investigated in normal Ringer's solution, and in a choline solution that clamps calcium near its resting level. For saturating intensities ranging from ∼102 to 104 Φ, the recovery phases of the responses in choline were nearly invariant in form. Responses in Ringer's were similarly invariant for saturating intensities from ∼103 to 104 Φ. In both solutions, recoveries to flashes in these intensity ranges translated on the time axis a constant amount (τc) per e-fold increment in flash intensity, and exhibited exponentially decaying “tail phases” with time constant τc. The difference in recovery half-times for responses in choline and Ringer's to the same saturating flash was 5–7 s. Above ∼104 Φ, recoveries in both solutions were systematically slower, and translation invariance broke down. Theoretical analysis of the translation-invariant responses established that τc must represent the time constant of inactivation of the disc-associated cascade intermediate (R*, G*, or PDE*) having the longest lifetime, and that the cGMP hydrolysis and cGMP-channel activation reactions are such as to conserve this time constant. Theoretical analysis also demonstrated that the 5–7-s shift in recovery half-times between responses in Ringer's and in choline is largely (4–6 s) accounted for by the calcium-dependent activation of guanylyl cyclase, with the residual (1–2 s) likely caused by an effect of calcium on an intermediate with a nondominant time constant. Analytical expressions for the dim-flash response in calcium clamp and Ringer's are derived, and it is shown that the difference in the responses under the two conditions can be accounted for quantitatively by cyclase activation. Application of these expressions yields an estimate of the calcium buffering capacity of the rod at rest of ∼20, much lower than previous estimates

Evolution of Baryon-Free Matter Produced in Relativistic Heavy-Ion Collisions

A 3-fluid hydrodynamic model is introduced for simulating heavy-ion collisions at incident energies between few and about 200 AGeV. In addition to the two baryon-rich fluids of 2-fluid models, the new model incorporates a third, baryon-free (i.e. with zero net baryonic charge) fluid which is created in the mid-rapidity region. Its evolution is delayed due to a formation time $\tau$, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After formation it thermalizes and starts to interact with the baryon-rich fluids. It is found that for $\tau$=0 the interaction strongly affects the baryon-free fluid. However, at reasonable finite formation time, $\tau$=1 fm/c, the effect of this interaction turns out to be substantially reduced although still noticeable. Baryonic observables are only slightly affected by the interaction with the baryon-free fluid.Comment: 17 pages, 3 figures, submitted to the issue of Phys. of Atomic Nuclei dedicated to S.T. Belyaev on the occasion of his 80th birthday, typos correcte

Quark Model and Neutral Strange Secondary Production by Neutrino and Antineutrino Beams

The experimental data on $K^0$ and $\Lambda$ production by $\nu$ and $\bar{\nu}$ beams are compared with the predictions of quark model assuming that the direct production of secondaries dominates. Disagreement of these predictions with the data allows one to suppose that there exists considerable resonance decay contribution to the multiplicities of produced secondaries.Comment: 6 pages, no figures, 2 table

Chemical Freeze-out of Strange Particles and Possible Root of Strangeness Suppression

Two approaches to treat the chemical freeze-out of strange particles in hadron resonance gas model are analyzed. The first one employs their non-equillibration via the usual \gamma_s factor and such a model describes the hadron multiplicities measured in nucleus-nucleus collisions at AGS, SPS and RHIC energies with \chi^2/dof = 1.15. Surprisingly, at low energies we find not the strangeness suppression, but its enhancement. Also we suggest an alternative approach to treat the strange particle freeze-out separately, but with the full chemical equilibration. This approach is based on the conservation laws which allow us to connect the freeze-outs of strange and non-strange hadrons. Within the suggested approach the same set of hadron multiplicities can be described better than within the conventional approach with \chi^2/dof = 1.06. Remarkably, the fully equilibrated approach describes the strange hyperons and antihyperons much better than the conventional one.Comment: 6 pages, 5 figure

Broadband optical gain via interference in the free electron laser: principles and proposed realizations

We propose experimentally simplified schemes of an optically dispersive interface region between two coupled free electron lasers (FELs), aimed at achieving a much broader gain bandwidth than in a conventional FEL or a conventional optical klystron composed of two separated FELs. The proposed schemes can {\it universally} enhance the gain of FELs, regardless of their design when operated in the short pulsed regime