The Active Transport of Oxygen and Carbon Dioxide into the Swim-Bladder of Fish

The active transport of oxygen and carbon dioxide into the swim-bladder of fish is discussed. The rete mirabile is a capillary network which is involved in the gas secretion into the bladder. The rete is regarded as a counter-current multiplier. Lactic acid which is produced in the gas gland generates in the rete single concentrating effects for oxygen and carbon dioxide; i.e., for equal partial pressures the concentrations of the gases in the afferent rete capillaries are higher than those in the efferent ones. The single concentrating effects were calculated from measurements of sea robin blood (Root, 1931). The multiplication of these effects within the rete for different rete lengths and different transport rates was numerically evaluated. The calculated O2 and CO2 pressures in the bladder are in good agreement with the experimental results of Scholander and van Dam (1953). The descent velocities at equilibrium between bladder pressure and hydrostatic pressure are discussed for fishes with different rete lengths

Magnetic Resonance Investigation of the Human Brain after 6 Days of Acclimatization to 4554 m - Preliminary Results of the EFA study -

Objective: Hypoxia is the main trigger of acute mountain sickness (AMS). However it is not the cause of the actual symptoms of AMS. The biochemical mechanisms underlying the AMS development are not well understood what leads to a high uncertainty regarding the likeliness of AMS development in astronauts living in future moderate hypobaric hypoxic habitats on Mars or moon. The hypothesis of the EFA study (Edema Formation in the High Alps) was that hypoxia triggered inflammatory processes lead to a breakdown of the capillary barrier and edema formation in vulnerable tissues as the brain. Methods: 11 subjects (5 women) ascended within 48 h from 1154 m to the Capanna Regina Margherita in 4554 m. Brain magnetic resonance imaging (MRI) was performed at sea level before the altitude exposure and within the first 12 h after descent. MRI included amongst others an anatomical 3D volumetric T1-weighted MPRAGE (magnetization-prepared rapid acquisition of gradient echo) scan, a susceptibility weighted gradient echo sequence, T2 weighted spin echo sequences and a diffusion weighted sequence to gain an apparent diffusion coefficient mapping and a trace image to test for volume changes of the different brain compartments, for hypoxic triggered brain edema and for micro-bleedings. Baseline measurements were performed at the DLR MRI lab in Cologne (77 m) whereas post line measurements were performed at the MRI department of the German Air Force in Fürstenfeldbruck (517 m) by applying identical sequences at both centers. Results: Neither mean global intracranial volume (p=7.97) nor mean volumes of the particular brain compartments grey (p=0.279) and white matter (p=0.758) or cerebrospinal fluid (p=0.586) showed any significant differences after the altitude exposure with respect to baseline. However 6 days of altitude exposure lead to the exacerbation of pre-existing white matter lesions in one subject and the occurrence of a local hypoxic edema in the splenium of a second subjects in the sense of a reversible splenial lesion syndrome (RESLES) (1, 2). Conclusion: Contradictory to the current literature (3) we were not able to show a general volume gain of the intracranial compartments after high altitude adaptation. However our findings of white matter lesions (4) and RESLES in two subjects not presenting any symptoms of a high altitude cerebral edema (HACE) have, as far as we know, not been described before (5)

Determinisitic Optical Fock State Generation

We present a scheme for the deterministic generation of N-photon Fock states from N three-level atoms in a high-finesse optical cavity. The method applies an external laser pulsethat generates an $N$-photon output state while adiabatically keeping the atom-cavity system within a subspace of optically dark states. We present analytical estimates of the error due to amplitude leakage from these dark states for general N, and compare it with explicit results of numerical simulations for N \leq 5. The method is shown to provide a robust source of N-photon states under a variety of experimental conditions and is suitable for experimental implementation using a cloud of cold atoms magnetically trapped in a cavity. The resulting N-photon states have potential applications in fundamental studies of non-classical states and in quantum information processing.Comment: 25 pages, 9 figure

Dynamic generation of maximally entangled photon multiplets by adiabatic passage

The adiabatic passage scheme for quantum state synthesis, in which atomic Zeeman coherences are mapped to photon states in an optical cavity, is extended to the general case of two degenerate cavity modes with orthogonal polarization. Analytical calculations of the dressed-state structure and Monte Carlo wave-function simulations of the system dynamics show that, for a suitably chosen cavity detuning, it is possible to generate states of photon multiplets that are maximally entangled in polarization. These states display nonclassical correlations of the type described by Greenberger, Horne, and Zeilinger (GHZ). An experimental scheme to realize a GHZ measurement using coincidence detection of the photons escaping from the cavity is proposed. The correlations are found to originate in the dynamics of the adiabatic passage and persist even if cavity decay and GHZ state synthesis compete on the same time scale. Beyond entangled field states, it is also possible to generate entanglement between photons and the atom by using a different atomic transition and initial Zeeman state.Comment: 22 pages (RevTeX), including 23 postscript figures. To be published in Physical Review

Cross-generational trans fat intake exacerbates UV radiation-induced damage in rat skin

AbstractWe evaluated the influence of dietary fats on ultraviolet radiation (UVR)-induced oxidative damage in skin of rats. Animals from two consecutive generations born of dams supplemented with fats during pregnancy and breastfeeding were maintained in the same supplementation: soybean-oil (SO, rich in n-6 FA, control group), fish-oil (FO, rich in n-3 FA) or hydrogenated-vegetable-fat (HVF, rich in TFA). At 90days of age, half the animals from the 2nd generation were exposed to UVR (0.25J/cm2) 3×/week for 12weeks. The FO group presented higher incorporation of n-3 FA in dorsal skin, while the HVF group incorporated TFA. Biochemical changes per se were observed in skin of the HVF group: greater generation of reactive oxygen species (ROS), lower mitochondrial integrity and increased Na+K+-ATPase activity. UVR exposure increased skin wrinkles scores and ROS generation and decreased mitochondrial integrity and reduced-glutathione levels in the HVF group. In FO, UVR exposure was associated with smaller skin thickness and reduced levels of protein–carbonyl, together with increased catalase activity and preserved Na+K+-ATPase function. In conclusion, while FO may be protective, trans fat may be harmful to skin health by making it more vulnerable to UVR injury and thus more prone to develop photoaging and skin cancer

Resonance fluorescence of a trapped three-level atom

We investigate theoretically the spectrum of resonance fluorescence of a harmonically trapped atom, whose internal transitions are $\Lambda$--shaped and driven at two-photon resonance by a pair of lasers, which cool the center--of--mass motion. For this configuration, photons are scattered only due to the mechanical effects of the quantum interaction between light and atom. We study the spectrum of emission in the final stage of laser--cooling, when the atomic center-of-mass dynamics is quantum mechanical and the size of the wave packet is much smaller than the laser wavelength (Lamb--Dicke limit). We use the spectral decomposition of the Liouville operator of the master equation for the atomic density matrix and apply second order perturbation theory. We find that the spectrum of resonance fluorescence is composed by two narrow sidebands -- the Stokes and anti-Stokes components of the scattered light -- while all other signals are in general orders of magnitude smaller. For very low temperatures, however, the Mollow--type inelastic component of the spectrum becomes visible. This exhibits novel features which allow further insight into the quantum dynamics of the system. We provide a physical model that interprets our results and discuss how one can recover temperature and cooling rate of the atom from the spectrum. The behaviour of the considered system is compared with the resonance fluorescence of a trapped atom whose internal transition consists of two-levels.Comment: 11 pages, 4 Figure

Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion

We describe the results of a parametric down-conversion experiment in which the detection of one photon of a pair causes the other photon to be switched into a storage loop. The stored photon can then be switched out of the loop at a later time chosen by the user, providing a single photon for potential use in a variety of quantum information processing applications. Although the stored single photon is only available at periodic time intervals, those times can be chosen to match the cycle time of a quantum computer by using pulsed down-conversion. The potential use of the storage loop as a photonic quantum memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe

Spatial Light Modulators for the Manipulation of Individual Atoms

We propose a novel dipole trapping scheme using spatial light modulators (SLM) for the manipulation of individual atoms. The scheme uses a high numerical aperture microscope to map the intensity distribution of a SLM onto a cloud of cold atoms. The regions of high intensity act as optical dipole force traps. With a SLM fast enough to modify the trapping potential in real time, this technique is well suited for the controlled addressing and manipulation of arbitrarily selected atoms.Comment: 9 pages, 5 figure

Panspermia, Past and Present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space

Astronomically, there are viable mechanisms for distributing organic material throughout the Milky Way. Biologically, the destructive effects of ultraviolet light and cosmic rays means that the majority of organisms arrive broken and dead on a new world. The likelihood of conventional forms of panspermia must therefore be considered low. However, the information content of dam-aged biological molecules might serve to seed new life (necropanspermia).Comment: Accepted for publication in Space Science Review