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In this paper, we establish a framework of delta-sigma conversion of graph signals. First, we define delta-sigma conversion for graph signals by considering the corresponding conversion for standard time series signals. We next propose a conversion method based on spanning in-tree, for which it is proven that the method satisfies the conditions for delta-sigma conversion. The proposed method is demonstrated by numerical examples and application to halftone image processing.

Engineering optimization problems usually contain various constraints and mixed integer-discrete-continuous type of design variables. This article proposes an efficient particle swarm optimization (PSO) algorithm for such problems. First, the constrained optimization problem is transformed into an unconstrained problem without introducing any problem-dependent or user-defined parameters such as penalty factors or Lagrange multipliers, though such parameters are usually required in general optimization algorithms. Then, the above PSO method is extended to handle integer, discrete, and continuous design variables in a simple manner, yet with a high degree of precision. The proposed PSO scheme is fairly simple and thus it is easy to implement. In order to demonstrate the effectiveness of our method, several mechanical design optimization problems are solved, and the numerical results are compared with those reported in the literature.

ITER will be the first magnetic confinement device with burning DT plasma and fusion power of about 0.5 GW. Parameters of ITER plasma have been predicted using methodologies summarized in the ITER Physics Basis (1999 Nucl. Fusion 39 2175). During the past few years, new results have been obtained that substantiate confidence in achieving Q  10 in ITER with inductive H-mode operation. These include achievement of a good H-mode confinement near the Greenwald density at high triangularity of the plasma cross section; improvements in theory-based confinement projections for the core plasma, even though further studies are needed for understanding the transport near the plasma edge; improvement in helium ash removal due to the elastic collisions of He atoms with D/T ions in the divertor predicted by modelling; demonstration of feedback control of neoclassical tearing modes and resultant improvement in the achievable β-values; better understanding of edge localized mode (ELM) physics and development of ELM mitigation techniques; and demonstration of mitigation of plasma disruptions. ITER will have a flexibility to operate also in steady-state and intermediate (hybrid) regimes. The ‘advanced tokamak’ regimes with weak or negative central magnetic shear and internal transport barriers are considered as potential scenarios for steady-state operation. The paper concentrates on inductively driven plasma performance and discusses requirements for steady-state operation in ITER.

The diagnostic system of JT-60U (JT-60upgrade) is composed of about 50 individual diagnostic devices. Recently, the detailed radial profile measurements of plasma parameters have been improved, so that the internal structure of plasmas could be explored. The understanding of plasma confinement has been enhanced by density and temperature fluctuation measurements using a mm-wave reflectometer and electron cyclotron emission measurements, respectively. In addition, real-time control experiments of electron density, neutron yield, radiated power, and electron temperature gradient have been carried out successfully by corresponding diagnostic devices. These measurements and the real-time control contribute to improving plasma performance. Diagnostic devices for next generation fusion devices such as a CO2laser interferometer/polarimeter and a CO2laser collective Thomson scattering system have been developed.

Heat and particle control has been studied under the reactor-relevant high-power heating in the large tokamak of JT-60U with an open divertor and progressively a W-shaped pumped divertor. Heat and particle control is crucial for reduction in heat load onto the divertor plates, control of density in the main plasma, effective exhaust of helium ash, and reduction in impurity contamination. For the reduction of heat load, radiative divertor concept was developed based on understanding of heat and particle transport in scrape-off layer and divertor plasmas, which contributed to establishment of divertor concept in ITER. With argon injection, the total radiation loss power reached up to 80% of the net heating power with high confinement of HHy2~ 1, where HHy2is a confinement enhancement factor over the IPB98(y,2) ELMy H-mode scaling, at high density of 80% of the Greenwald density in the ELMy H-mode plasma. For the density control, the dependence of particle confinement on plasma parameters was systematically studied with two confinement times for center- and edge-fueled particles, which enabled discussion of density controllability. Core fueling using a high-field-side pellet injection extended the operation range of high confinement (HHy2~ 1) from 60 to 70% of the Greenwald density in the high βpELMy H-mode plasma. Efficient helium ash exhaust of τHe*/τE= 2.8 was demonstrated in the ELMy H-mode plasma with the pumping from the private flux region, which is the same pumping geometry as that in ITER design. Reduction in Zeffby puff-and-pump scheme was demonstrated, and chemical sputtering yields were estimated with the consideration of not only methane but also heavier hydrocarbons. Their sputtering yields showed strong dependence on the wall temperature and weak dependence on the particle flux. The measured profiles of C II and C IV line intensities were well reproduced by the Monte Carlo impurity transport simulation code (IMPMC code). The estimation of sputtering yields and development of the simulation code enabled reliable predictions for impurity behavior in a fusion reactor.

Fusion plasma performance and confinement studies on JT-60 and JT-60U are reviewed. With the main aim of providing a physics basis for ITER and the steady-state tokamak reactors, JT-60/JT-60U has been developing and optimizing the operational concepts, and extending the discharge regimes toward sustainment of high integrated performance in the reactor relevant parameter regime. In addition to achievement of high fusion plasma performances such as the equivalent breakeven condition (QDTequp to 1.25) and a high fusion triple product nD(0)τETi(0) = 1.5 × 1021m-3skeV, JT-60U has demonstrated the integrated performance of high confinement, high βN, full non-inductive current drive with a large fraction of bootstrap current. These favorable performances have been achieved in the two advanced operation regimes, the reversed magnetic shear (RS) and the weak magnetic shear (high-βp) ELMy H modes characterized by both internal transport barriers (ITB) and edge transport barriers (ETB). The key factors in optimizing these plasmas towards high integrated performance are control of profiles of current, pressure, rotation, etc. utilizing a variety of heating, current drive, torque input, and particle control capabilities and high triangularity operation. As represented by discovery of ITBs (density ITB in the central pellet mode, ion temperature ITB in the high-βpmode, and electron temperature ITB in the reversed shear mode), confinement studies in JT-60/JT-60U have been emphasizing freedom and also restriction of radial profiles of temperature and density. In addition to characterization of confinement and analyses of transport properties of the OH, the L-mode, the H-mode, the pellet mode, the high-βpmode, and the RS mode, JT-60U has clarified formation conditions, spatial structures and dynamics of edge and internal transport barriers, and evaluated effects of repetitive MHD events on confinement such as sawteeth and ELMs. Through these studies, JT-60U has demonstrated applicability of the high confinement modes to ITER and the steady-state tokamak reactors.

The chemical sputtering yields of CH₄/CD₄ and C₂H_x/C₂D_x have been measured at the divertor plates of JT-60U. Spectroscopic measurements for CH/CD and C₂ spectral bands are applied to estimate the CH₄/CD₄ and the C₂H_x/C₂D_x flux. At the surface temperatures of 380, 440 and 560 K, the CH₄ yield is, respectively, ~0.8%, 1-2% and 2-3%, the C₂H_x yield 1-2%, 3-4% and 4-5%, and the total sputtering yield by hydrogen ions 3-4%, ~8% and ~10%. With increasing ion flux to the divertor plates (Γ_ion), the sputtering yields (Y) decrease, i.e. Y∝Γ_ion^{(-0.05 to -0.40)}. With increasing electron temperature (T_e), the sputtering yields increase, i.e. Y∝T_e^0.5. It is concluded from the result of regression analysis of Y∝T_e^0.5 that the negative dependence of the yields on the ion flux is attributed to the incident ion energies to the carbon plates. The ratio of the sputtering yields by deuterium ions and hydrogen ions is estimated to be ≥1.5 based on the ion flux measurement by H_α/D_α intensity. The C₂H_x/C₂D_x sputtering yield accounts for ~80% of the total number of sputtered carbon atoms.

A radiative divertor experiment with neon gas puff was carried out with the aim of investigating impurity behaviour, after the open divertor was modified to the pumped W-shaped divertor. To evaluate neon radiation, we analysed lines from the neon ion measured with a VUV spectrometer in the divertor plasma. As a result, lines from Ne IV-Ne VIII were identified. By combining the measurement of an absolutely calibrated multichannel interference filter spectrometer with that of the VUV spectrometer, the radiation loss through neon line emission was estimated in the divertor plasma. In the case of pumping-off, the detached plasma evolved into multifaceted asymmetric radiation from the edge (MARFE). It was observed that the line intensities of highly ionized neon (Ne VII, Ne VIII) increased simultaneously with the formation of the MARFE and furthermore increased after the MARFE formation. It is considered that after the divertor plasma was detached, the plasma flow velocity and the friction force were weaker in the case of pumping-off than in the case of pumping-on and more impurities moved toward the X-point region. These observations imply impurity back flow from the divertor upstream by the reduction of friction force.

Taking account of the plant nonlinearity, we propose a controller design method which consists of H∞control and exact linearization via nonlinear state feedback. The latter one is designed to yield the linear system which exactly equals to the linearization of the plant around an equilibrium point. We illustrate the validity of our method by experiments.

This paper is concerned with the problem to find a controller which satisfies (a) internal stability, (b) the robust tracking, (c) the exact model matching and (d) the specified H 00 control performance related to the feedback properties. First, we give a necessary and sufficient condition for such a controller to exist. Second, we characterize all such controllers, where (i) the two-degree-of-freedom compensator configuration and (ii) the free parameter of the H∞ suboptimal controller are fully exploited, Third, we evaluate the effectiveness of our control method by tlte experiment using a magnetic bearing system.

This paper is concerned with the parametrization of nonlinear state feedback controllers via kernel representations. First we define an appropriate stability for state feedback systems. Second it is shown that the stability condition can be reduced to the internal stability of a specific type of output feedback system. Finally the state feedback parametrization will be derived based on the existing output feedback parametrization. Furthermore, the robustness of state feedback systems is discussed.

As an R&D task of the ITER engineering design activities (EDA), we carried out the irradiation tests on the basic materials of transmission components such as ceramics, windows, fiber optics and mirrors, and in-vessel diagnostics sensors such as magnetic probes and bolometers. Ceramics will be used as general insulating materials. Here we investigated the radiation induced conductivity (RIC) of ceramics for 14 MeV neutrons. Optical elements are the most sensitive to radiation damages among the transmission components. Radiation induce transmission loss of window materials and fiber optics have been measured in the Japan material testing reactor (JMTR). Off line irradiation tests were carried out for molybdenum corner cube reflector (CCR) and gold coated mirrors in JMTR also. Fourteen MeV-neutron-induce luminescence of window material was evaluated in the fusion neutronics source (FNS). Bolometers should be installed inside the vacuum vessel to measure the radiation losses in the infra red to soft X-ray range. We demonstrated the performance of the JT 60 type bolometer under 60Co gamma-rays.

Antisera against components of unfertilized mouse eggs other than zonae pellucidae were produced in 3 male rabbits and the effects of the antisera on fertilization were studied in the mouse. The antibody titers determined by using zona-free eggs in the cytotoxic test were 2−4to 2−6. Treatment of eggs in vitro or passive immunization of female mice with antisera No. 1 and No. 3 did not inhibit fertilization, but treatment of intact eggs and passive immunization with antiserum No. 2 did inhibit fertilization. It was considered that the inhibition of fertilization after treatment of eggs or passive immunization of females with antiserum No. 2 was due to the contaminating antibody against the zona pellucida. The fertilizing capacity of spermatozoa was suppressed by treatment of sperm with all 3 antisera. The inhibitory effect of antiserum on fertilizing capacity of sperm disappeared, however, after absorption of antiserum with the ovary but not with liver or kidney. It is possible that spermatozoa and egg components other than the zona pellucida have a common antigen which induces an antibody which suppresses the fertilizing capacity of spermatozoa.

This paper is concerned with an iterative learning control law. This control law enable us to find a control input automatically that produces the desired output exactly over a finite time interval by some iteration rule, even if only the partial knowledge of the object system to be controlled is available. First, we derive a sufficient condition for a general class of systems to achieve the desired output by the iterative learning control scheme in both continuous and discrete time cases. This result clarifies that the direct transmission term of the object systems plays a crucial role in the error convergence. Second, based on this result, we clarify the class of systems to which the learning control law is applicable. Furthermore, we briefly discuss the design of learning control systems.

Summary.A significantly higher survival rate was obtained when frozen—thawed morulae were transferred to oviducts of recipients ovulating after donors rather than to those of synchronized or earlier ovulating recipients. The highest proportion of live young, 23%, was obtained after transfer of eggs to recipients ovulating 18 h after donors. The proportion of live young (48%) was significantly increased when frozen—thawed rabbit morulae were transferred into both oviducts of recipients at this stage.

To aid in designing high-speed optical networks, the fundamental limitations of lightwave transmission systems are investigated from the viewpoint of fibre nonlinearities, particularly of stimulated Brillouin scattering (SBS). When SBS occurs, the fibre launch power is usually restricted; thus, SBS is detrimental to lightwave systems. The effects of SBS on signals transmitted in fibres are clarified for several modulation schemes, especially coherent modulation schemes. A generalized model based on the maximum power spectrum density in the signals is proposed to estimate the degree of SBS generation. The maximum repeaterless transmissions for various bit rates, laser diode linewidths, and Brillouin gains of optical fibres are presented. The degradation of transmission due to SBS is clarified experimentally, focusing on the bit error rate, fibre input power, and spectra of signals transmitted in fibres. In addition, various techniques for suppressing the SBS effects are proposed. A repeaterless transmission experiment conducted over 364.3 km using optical booster amplifiers is presented to verify the effectiveness of the SBS suppression technique.

CD/CH-band intensities emitted from hydrocarbon molecules have been measured in the divertor region of JT-60U and the chemical sputtering yield of methane was estimated as a function of the surface temperature and the deuterium ion flux. The chemical sputtering yield increases with the surface temperature and decreases with increasing ion flux density in the L-mode plasmas. The B 4 C converted CFC tiles are installed in JT-60U and it is found that the chemical sputtering of B 4 C converted CFC tiles is suppressed in comparison to normal CFC tiles.

The many closely crowded lines (pseudo-continuum) of high-Z gold impurities are studied in detail with a calibrated grazing-incidence monochromator in hydrogen plasma, in the upgraded DIVA tokamak device with a divertor; the toroidal field is 20 kG and the peak plasma current is 40 kA. The emission spectrum of the many lines is observed in the wavelength region of 42 to 200 Å. The time-resolved spatial distribution of the emission of the many lines was measured in each element in the wavelength region. It was found that the radiation due to the many lines in the wavelength region of 120 to 200 Å concentrated in an intermediate region of the plasma column, and that the emission of the many lines in the wavelength region of 42-110 Å peaked at the plasma centre. The radiation power loss due to the many lines in the 120-200 Å region was dominant during the whole discharge. The radiation power due to the many lines corresponded to 40-70% of the total radiation power loss from the plasma volume.

ICRF heating experiments were carried out in the JFT-2 tokamak with pure high-field-side excitation. Almost pure electron and ion heating regimes were made possible in the experiment so that the metal impurities were reduced. Power balance of the plasma heated by ICRF is revealed by a transport analysis of the experimental results. RF power deposition profiles of each heating regime are obtained. The results of this analysis may serve as an experimental basis for refining the present theoretical treatment of ICRF heating.

Deuterium and hydrogen energy spectra during ICRF heating as well as nH/nDwere measured with the E||B type mass-separated neutral particle energy analyser. High-energy tails of deuterium and hydrogen were observed in the dilute-minority case. From Fokker-Planck calculations of the charge-exchange spectrum and power-balance analysis it is shown that second-harmonic cyclotron damping by the majority deuterium is the dominant mechanism of ion heating in the dilute-minority case.

ICRF heating of impurity-free tokamak plasmas is studied in DIVA. The frequency is fixed at 25 MHz, which is a second-harmonic cyclotron frequency of deuteron with a toroidal magnetic field of 16.4 kG. The toroidal field BTand the ratio of proton-to-deuteron density pare varied over ranges of 12 ? BT? 19 kG and 2 p40%, respectively. The most favourable ion heating is obtained at BT= 18 kG and p= 5 ~ 10%. Ion temperature increases from 200 to 300 eV were measured by charge-exchange neutral analysis and also by spectroscopy, where 100 kW RF net power were applied. The results are consistent with mode-conversion theory.

This paper introduces the canonical transformation for the generalized Hamiltonian systems, which preserves the generalized Hamiltonian structure of the original system and is expected to provide new insights and useful tools for analysis and synthesis of such systems. First, the class of such transformations and some of their properties are clarified. Second, we show how to stabilize the generalized Hamiltonian systems by using the transformation. This method works even when we can not stabilize them by conventional unity feedback without canonical transformation. Furthermore, it is shown that the proposed stabilization method includes the well-known one which exploits the virtual potential energy as a special case.

Impurities in JT-60 were studied by visible and VUV spectroscopy over two periods of operation. The two periods were distinguished by the use of different first wall materials: from April 1985 to March 1987, TiC coated molybdenum was used as limiter material; from June to October 1987, graphite was used. Quantitative spectroscopic measurements of Zeff, impurity concentrations and radiated power losses were made for ohmically heated and neutral beam heated discharges with limiter and divertor configurations. In the first phase with metallic first wall material, oxygen, carbon and titanium were identified as the main plasma impurities. In neutral beam heated, diverted discharges, Zeffwas 1.6 at e= 4 × 1019m?3. The concentrations of oxygen, carbon and titanium were 1%, 0.1% and 0.006% of ne, respectively. In the second phase with graphite material, the metallic impurities were reduced, and the contribution of metallic impurities to the radiated power loss was less than 1%. However, Zeffincreased up to 3 in neutral beam heated discharges. In limited plasmas, the concentrations of oxygen and carbon were 1% and 5%, respectively, at e= 4 × 1019m?3; in diverted plasmas, these concentrations were 2% and 0.4% at the same e. The radiated power loss from the main plasma was 20-40% of the input power in neutral beam heated, limited discharges, and 7-25% in diverted discharges. The contributions of oxygen and carbon to the radiated power in limited discharges were comparable, and in diverted discharges the contribution of oxygen was dominant.

The active beam scattering method was applied to ion temperature measurements in JT-60 plasmas. The ion temperature found was in reasonable agreement with that obtained from Doppler broadening of the Ti XXI and Ti XXII resonance lines in the temperature range of 1.5 to 10 keV. With the help of the scattering system, the central ion temperature of JT-60 plasmas during 40 keV and 70-75 keV NBI heating was measured. Higher ion temperature was obtained during 70 to 75 keV than during 40 keV NBI heating. These data and a possible explanation are presented. A numerical simulation of this diagnostic indicates that the ion temperature as deduced from the diagnostic is almost equal to the bulk temperature when the ratio of high energy ion component to the total ion stored energy is less than 0.3.

The impurity transport characteristics of ohmically and neutral beam heated diverted plasmas in JT-60 have been studied. In sawtoothfree, ohmically heated plasmas with Ip= 1.5 MA, e= (2?3) × 1019m?3, q(a) = 3.2, no radiation buildup is observed. The temporal evolution of injected titanium has been measured by VUV and X-ray crystal spectrometers and PIN diodes. The spectral lines of Ti XX (259.3 Å) and Ti XXI (2.6097 Å) are compared with one-dimensional diffusive/convective impurity transport calculations. The transport calculations for Ohmic discharges with Ip= 1.5?2 MA, e= (1-3) × 1019m-3, q(a) = 3?3.7, show that DA=(1?2) m2s?1and that the inward convective velocity is small. In neutral beam heated plasmas with Ip= 1.5 MA, e= 4 × 1019m-3, q(a)= 3.6, Pb= 8 MW, no difference is observed in the global time evolution of the Ti XXI line emissions between co- and counter-injected discharges. The experimental observations are well represented by choosing DA= (1-2) m2s?1and a small inward velocity.

Characteristics are presented of the energy confinement time resulting from neutral hydrogen beam heating of JT-60 tokamak plasmas with a plasma current, Ip, of 1-2 MA, a line averaged electron density, e, of 1.5-7 × 1019m?3and an absorbed beam power, Pabs, up to 20 MW. The plasma energy content follows an offset linear relation to the absorbed power. The incremental energy confinement time for thermal components, , is almost independent of Ipand eat 60 ms, while the incremental energy confinement time for the total plasma energy, , decreases with plasma density. The value of in JT-60 coincides with the prediction of the Shimomura-Odajima scaling of L-mode discharges.

Impurity contamination and radiation power have been studied with a vacuum UV monochromator (10-1300 Å) on JFT-2 for typical 160-kA and 18-kG hydrogen discharges. Oxygen has been found to be a dominant impurity element (5-7% of the electron density) and to be radially distributed according to the ionization sequence. The ground level population densities of the O6+and O7+ions in the central hot region have been determined, and that of fully ionized oxygen has been also estimated, combined with enhanced bremsstrahlung radiation measurement. The radial profile of the effective ionic charge Zeffhas been determined from that of the impurity ions. The Zeffvalue has been found to be consistent with the value derived from the electrical conductivity. The total power of line radiation from the first resonance transitions of the oxygen ions amounts to 100-50 kW (34-17% of Joule heating power).

A pulse of methane gas and a short burst of aluminium have been injected into DIVA plasma at the point farthest from the divertor. For the same amount of injected impurity, the accumulation of injected impurity in the main plasma is reduced by a factor of 2 to 4 by the action of the divertor. The impurity shielded by the scrape-off plasma is rapidly guided into the burial chamber. The time needed for the poloidal excursion of the injected impurity ions in the scrape-off layer is roughly equal to that of the scrape-off plasma. Sweeping-out of the impurity ions diffusing from the main plasma into the burial chamber is also observed.

The radiation loss in DIVA is measured quantitatively by a pyroelectric detector calibrated by heavily contaminated resistive discharges. The results are: (1) radiation loss power due to low-Z impurities does not play an important role; (2) radiation loss power due to the pseudo-continuum from high-Z impurities affects the power balance of the confined plasma; (3) the time dependence of energy loss channels is clarified in the gross power balance, a fact which attests to the reliability of the radiation measurements carried out by the pyroelectric detector.

A pulse of methane gas is injected into the DIVA tokamak. The major portion of the injected impurity is shielded by the outer edge plasma, i.e. only 20% of the injected carbon are introduced into the discharge. After radial penetration of the injected carbon has been accomplished, accumulation doubles and a new steady state is sustained over the period of proton confinement. The transient radial diffusion process of the carbon is compared with calculations using an impurity transport code. The behaviour of the carbon impurity in the whole minor radius is well described by assuming perfect re-cycling at the gold-plated shell surface and using neoclassical diffusion superposed by anomalous diffusion of protons. It is shown that spreading caused by anomalous diffusion is important. The calculated result indicates that the carbon ions are lost dominantly in a He-like state.

It is shown that the presence of a clean gold shell surface and titanium gettering of the burial chamber reduce light impurities in the DIVA plasma significantly.Formation and discharge characteristics of the light-impurity free plasma are presented.

In this paper we study linear time-invariant multi variable systems including both feedforward and feedback compensators. Firstly, a condition for the system to be an internally stable robust tracking system is obtained. Secondly, the class of attainable transfer matrices from reference signal to plant output of internally stable robust tracking systems is clarified. Thirdly, measures of the sensitvity and the stability margin are given, and a simple method is proposed for setting these quantities to desirable ones Finally, based on these results, we propose a synthesis procedure of robust tracking systems with desirable transient responses, sensitivity and stability margin.

17β-Oestradiol was administered intramuscularly to twentyeight heifers either before, simultaneously with or after a subcutaneous injection of 3000 i.u. of pregnant mares' serum (pms). This was followed by an intravenous injection of 2000 i.u. ofhuman chorionic gonadotrophin (hcg). The animals were bred and slaughtered, the reproductive tract flushed and the ova examined microscopically.Oestrogen treatment tended to reduce the number of developed follicles when applied before pms, but it significantly increased the number when applied after pms. The proportion of follicles which ovulated was not affected by oestrogen. In a group treated with oestrogen after pms, the number of fertilized ova per cow ranged from six to seventeen with an average of 11·3 which was considered an improvement over superovulated cattle not treated with oestrogen. There was no evidence that the rate of tubal transport of ova was altered by the oestrogen therapy applied.

Embryos were recovered from super-ovulated rabbits and transferred to beef cattle. Three techniques of embryo transfer were attempted: (a) non-surgical, (b) non-surgical with CO2insufflation, using the “Kidde” insufflator and (c) surgical via a paralumbar laparotomy. An apparatus made of three plastic tubes and two long metal needles was used to by-pass the cervix and to transfer the embryos non-surgically into the uterus. Carbon dioxide insufflation through the cervix was essential for successful transfer. This non-surgical technique was inferior to the surgical technique in terms of percent of embryos successfully transferred. Viable rabbit embryos of 16- and 32-cell stages developed to the blastocyst stage in the cow's uterus.Embryos were recovered from super-ovulated cattle and transferred by laparotomy to the Fallopian tubes or uteri of 1-, 2-, 3- and 4-day pseudopregnant rabbits. Viable cattle embryos of 1- to 8-cell stages failed in most cases to cleave when kept for 48 hr. in the genitalia of pseudopregnant rabbits.