Description of concept and first feasibility test results of a life support subsystem of the Botany Facility based on water reclamation

The Botany Facility allows the growth of higher plants and fungi over a period of 6 months maximum. It is a payload planned for the second flight of the Eureca platform around 1990. Major tasks of the Life Support Subsystem (LSS) of the Botany Facility include the control of the pressure and composition of the atmosphere within the plant/fungi growth chambers, control of the temperature and humidity of the air and the regulation of the soil water content within specified limits. Previous studies have shown that various LSS concepts are feasible ranging from heavy, simple and cheap to light, complex and expensive solutions. A summary of those concepts is given. A new approach to accomplish control of the temperature and humidity of the air within the growth chambers based on water reclamation is discussed. This reclamation is achieved by condensation with a heat pump and capillary transport of the condensate back into the soil of the individual growth chamber. Some analytical estimates are given in order to obtain guidelines for circulation flow rates and to determine the specific power consumption

Energy Balance in the Solar Transition Region. IV. Hydrogen and Helium Mass Flows With Diffusion

In this paper we have extended our previous modeling of energy balance in the chromosphere-corona transition region to cases with particle and mass flows. The cases considered here are quasi-steady, and satisfy the momentum and energy balance equations in the transition region. We include in all equations the flow velocity terms and neglect the partial derivatives with respect to time. We present a complete and physically consistent formulation and method for solving the non-LTE and energy balance equations in these situations, including both particle diffusion and flows of H and He. Our results show quantitatively how mass flows affect the ionization and radiative losses of H and He, thereby affecting the structure and extent of the transition region. Also, our computations show that the H and He line profiles are greatly affected by flows. We find that line shifts are much less important than the changes in line intensity and central reversal due to the effects of flows. In this paper we use fixed conditions at the base of the transition region and in the chromosphere because our intent is to show the physical effects of flows and not to match any particular observations. However, we note that the profiles we compute can explain the range of observed high spectral and spatial resolution Lyman alpha profiles from the quiet Sun. We suggest that dedicated modeling of specific sequences of observations based on physically consistent methods like those presented here will substantially improve our understanding of the energy balance in the chromosphere and corona.Comment: 50 pages + 20 figures; submitted to ApJ 9/10/01; a version with higher resolution figures is available at http://cfa-www.harvard.edu/~avrett

Proposal for an Experiment to Test a Theory of High Temperature Superconductors

A theory for the phenomena observed in Copper-Oxide based high temperature superconducting materials derives an elusive time-reversal and rotational symmetry breaking order parameter for the observed pseudogap phase ending at a quantum-critical point near the composition for the highest $T_c$. An experiment is proposed to observe such a symmetry breaking. It is shown that Angle-resolved Photoemission yields a current density which is different for left and right circularly polarized photons. The magnitude of the effect and its momentum dependence is estimated. Barring the presence of domains of the predicted phase an asymmetry of about 0.1 is predicted at low temperatures in moderately underdoped samples.Comment: latex, 2 figure

Spontaneous time reversal symmetry breaking in the pseudogap state of high-Tc superconductors

When matter undergoes a phase transition from one state to another, usually a change in symmetry is observed, as some of the symmetries exhibited are said to be spontaneously broken. The superconducting phase transition in the underdoped high-Tc superconductors is rather unusual, in that it is not a mean-field transition as other superconducting transitions are. Instead, it is observed that a pseudo-gap in the electronic excitation spectrum appears at temperatures T* higher than Tc, while phase coherence, and superconductivity, are established at Tc (Refs. 1, 2). One would then wish to understand if T* is just a crossover, controlled by fluctuations in order which will set in at the lower Tc (Refs. 3, 4), or whether some symmetry is spontaneously broken at T* (Refs. 5-10). Here, using angle-resolved photoemission with circularly polarized light, we find that, in the pseudogap state, left-circularly polarized photons give a different photocurrent than right-circularly polarized photons, and therefore the state below T* is rather unusual, in that it breaks time reversal symmetry11. This observation of a phase transition at T* provides the answer to a major mystery of the phase diagram of the cuprates. The appearance of the anomalies below T* must be related to the order parameter that sets in at this characteristic temperature .Comment: 11 pages, 4 figure

Disorder-driven quantum phase transition from antiferromagnetic metal to insulating state in multilayered high-Tc cuprate (Cu,C)Ba2Ca4Cu5Oy

We report on superconducting(SC) characteristics for oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba2Ca4Cu5Oy(Cu-1245(OPT)), which includes five-fold outer planes (OP) and four-fold inner planes (IP).As a result of the reduction of the carrier density, the bulk SC for Cu-1245 (OPT) takes place at the nearly optimally-doped OP with Tc= 98 K that is different from previously-reported Cu-1245(OVD) where IP plays a primary role for the onset of SC. It gives an evidence that the carrier density of the optimally-doped layer determines its bulk Tc.Static antiferromagnetic(AFM) order is evidenced at IP's by zero-field Cu-NMR at low temperature, irrespective of the SC transition at OP's below 98K. This AFM state at IP's is characterized by a carrier localization at low temperatures due to disorder effect, whereas the carrier densities in each layer are similar to Hg-1245(OPT) where the AFM metallic state are realized in IP's. This finding reinforces the phase diagram in which the AFM metallic phase exists between AFM insulator and SC states for the case of ideally-flat CuO2 plane without disorder.Comment: 4 pages, 5 figure

Truncation of a 2-dimensional Fermi surface due to quasiparticle gap formation at the saddle points

We study a two-dimensional Fermi liquid with a Fermi surface containing the saddle points $(\pi,0)$ and $(0,\pi)$. Including Cooper and Peierls channel contributions leads to a one-loop renormalization group flow to strong coupling for short range repulsive interactions. In a certain parameter range the characteristics of the fixed point, opening of a spin and charge gap and dominant pairing correlations are similar to those of a 2-leg ladder at half-filling. An increase of the electron density we argue leads to a truncation of the Fermi surface with only 4 disconnected arcs remaining.Comment: Reference added. RevTeX 4 pages incl. 4 ps file

Pseudogap and photoemission spectra in the attractive Hubbard model

Angle-resolved photoemission spectra are calculated microscopically for the two-dimensional attractive Hubbard model. A system of self-consistent T-matrix equations are solved numerically in the real-time domain. The single-particle spectral function has a two-peak structure resulting from the presense of bound states. The spectral function is suppressed at the chemical potential, leading to a pseudogap-like behavior. At high temperatures and densities the pseudogap diminishes and finally disappears; these findings are similar to experimental observations for the cuprates.Comment: 5 pages, 4 figures, published versio

Coherent quasiparticle weight and its connection to high-T_c superconductivity from angle-resolved photoemission

In conventional superconductors, the pairing energy gap (\Delta) and superconducting phase coherence go hand-in-hand. As the temperature is lowered, both the energy gap and phase coherence appear at the transition temperature T_c. In contrast, in underdoped high-T_c superconductors (HTSCs), a pseudogap appears at a much higher temperature T^*, smoothly evolving into the superconducting gap at T_c. Phase coherence on the other hand is only established at T_c, signaled by the appearance of a sharp quasiparticle (QP) peak in the excitation spectrum. Another important difference between the two types of superconductors is in the ratio of 2\Delta / T_c=R. In BCS theory, R~3.5, is constant. In the HTSCs this ratio varies widely, continuing to increase in the underdoped region, where the gap increases while T_c decreases. Here we report that in HTSCs it is the ratio z_A\Delta_m/T_c which is approximately constant, where \Delta_m is the maximum value of the d-wave gap, and z_A is the weight of the coherent excitations in the spectral function. This is highly unusual, since in nearly all phase transitions, T_c is determined by an energy scale alone. We further show that in the low-temperature limit, z_{\it A} increases monotonically with increasing doping x. The growth is linear, i.e. z_A(x)\propto x, in the underdoped to optimally doped regimes, and slows down in overdoped samples. The reduction of z_A with increasing temperature resembles that of the c-axis superfluid density.Comment: 11 pages, 5 figures, revised versio

Strongly Correlated Electrons and Neutron Scattering

Various aspects of close and interesting relationship between antiferromagnetism and singlet ground states are introduced for which neutron scattering have been playing vital roles. The special emphasis is on the disorder-induced antiferromagnetism in spin-Peierls systems, which can be viewed as a nucleation process of classical magnetic order in the background of singlet state whose origin is purely quantum-mechanical. It is then pointed out that similar features will be found in Ce_xCu_2Si_2 and high T_c cuprates. Finally the possible charge ordering process in NaV_2O_5 is discussed which leads to the quenching of localized spins.Comment: 8 pages, 3 figures, Proceedings of 7th ISSP International Symposium "Frontiers in Neutron Scattering Research" (To appear in J. Phys. Chem. Solids (1999)

Transport properties in the d-density wave state: Wiedemann-Franz law

We study the Wiedemann-Franz (WF) law in the d-density wave (DDW) model. Even though the opening of the DDW gap $(W_{0})$ profoundly modifies the electronic density of states and makes it dependent on energy, the value of the WF ratio at zero temperature (T=0) remains unchanged. However, neither electrical nor thermal conductivity display universal behavior. For finite temperature, with T greater than the value of the impurity scattering rate at zero frequency $\gamma(0)$ i.e. $\gamma(0)<T\ll W_{0}$, the usual WF ratio is obtained only in the weak scattering limit. For strong scattering there are large violations of the WF law.Comment: 1 figur