¹⁹F(p, n)¹⁹Ne, ¹⁶O(α, n)¹⁹Ne, and ²³Na(p, n)²³Mg endothermic reactions have been used to determine the mean lives of the excited states at 1508 and 1536 keV states in ¹⁹Ne and 451 keV state in ²³Mg by the Doppler shift attenuation method. The results are τ=(1.4_−0.6^+0.5)×10⁻¹² sec, τ=(2.8_−1.6^+1.8)×10⁻¹⁴ sec and τ=(3.6_−2.4^+9.1)×10⁻¹² sec respectively. From the measurement of gamma ray energies, the accurate energies of the excited state have been determined.

View full abstract

The decay of 6.3 min ^94mNb to levels of ⁹⁴Mo was studied with a Ge(Li) detector and a Ge(Li)–NaI(Tl) coincidence spectrometer. A 0.993-MeV gamma ray coincident with the 0.871-MeV gamma transition between the first excited and ground states of ⁹⁴Mo was found, and a level of ⁹⁴Mo at 1.864 MeV is proposed. A probable spin and parity assignment of 3⁺ is made to the 1.864-MeV level.

View full abstract

The ionization cross sections of Al–K, Cu–L, Mo–L, Ag–L and W–M shells have been presented for the incident ³He⁺ and ⁴He⁺ ions in the energy range from 45 to 90 keV/amu. The cross sections have been evaluated from the experimentally obtained thick target yields of characteristic X-rays, referring to the semiempirical stopping power data of helium ions. Contrary to the prediction by Born approximation, isotope dependence has been clearly ascertained in the ionization of target atoms. The quantitative analysis for Al–K shell ionization has shown that the collision process can be explained by the “binding theory”. The isotope dependence is mainly attributed to the Coulomb deflection difference of the isotopic projectiles near the target nucleus.

View full abstract

The lattice energies, infrared absorption frequencies and Debye characteristic temperatures have been calculated using a new logarithmic form A log_e(1+B⁄r⁹) for the overlap repulsion interaction for the alkali halide crystals containing lighter ions. The potential parameters A and B have been evaluated using room temperature lattice conditions. The necessary equation for the force constant, and infrared absorption frequency have been derived. The results have been compared with the experimental data as well as with calculated values from other methods. The logarithmic form for the overlap repulsion gives better results as compared with the Born-Mayer and Pauling’s potential energy functions.

View full abstract

Calculations of (1) the elastic scattering factor, (2) the inelastic scattering factor and (3) the linear Compton profile are carried out by use of the new wave function for an O⁻² atom in MgO by Yamashita and Asano (J. Phys. Soc. Japan 28 (1970) 1143). The comparison of the calculations of (1) and (3) with corresponding measurements has shown that the new wave function is definitely better than that by Watson (Phys. Rev. 111 (1958) 1108).

View full abstract

The effect of spatial dispersion on the electromagnetic wave propagation in the magnetplasma of semimetals is investigated with the spherical mass model. It is found that near the cyclotron harmonics propagating modes exist which correspond to the high frequency waves (HFW) in metals discussed by Platzman et al. By numerical calculations of the surface impedance it is found that the theory assuming weak spatial dispersion is promising for analyzing the cyclotron resonance absorption of semimetals.

View full abstract

The band structure of both paramagnetic and antiferromagnetic γMn is evaluated by G.F.M. with the Slater exchange approximation. The observed magnetic moment (2.3μ_B) is self-consistently obtainable, if the full Slater exchange is reduced by about one-half. The situation is the same at Cr. No special charactors are observed in E(k)-curves of γMn contrary to the case of Cr. Introducing a simple exchange interaction term −J_effδn² by the random phase approximation, we extend Mueller’s interpolation scheme to apply to the antiferromegnetic case, and antiferromagnetism in f.c.c. structure is examined within the limit of the rigid band approximation. If we assume the value J_eff=0.060Ry, f.c.c. Mn and f.c.c. Fe are antiferromagnetic and their magnetic moments are determined as 2.3μ_B and 0.7μ_B, respectively, which are in good agreement with experimental values. In f.c.c. structure the gap mechanism similar to Cr is found to be effective around N≈7.3. The theoretical prediction seems to be supported by experiments of γFeMn alloy.

View full abstract

General arguments given previously for the absence of singular enhancement of linear specific heat due to spin fluctuations in nearly antiferromagnetic metals are corrobolated by supplementing with arguments on special cases. Discussions are given on the possibility for stronger enhancement of linear specific heat in nearly two-dimensional metals than in usual three dimensional ones.

View full abstract

The phase transition for the spin systems described by the Hamiltonian
(Remark: Graphics omitted.)
is studied by means of the high-temperature series expansion of the zero field susceptibility. The first five terms in the susceptibility series are explicitly obtained for the two-dimensional square lattice in the cases of (i) 0≤ξ≤1, η=0 and (ii) 0≤ξ=η≤1. The critical temperature T_c and the critical exponent γ (susceptibility) are obtained as functions of the spin S and the anisotropy parameter ξ. The critical temperature has a finite value in the XY model (ξ=1, η=0) as well as the Heisenberg model (ξ=η=1). The simple formulae expressing T_c and γ valid for arbitrary S and ξ are proposed.

View full abstract

The heat capacities of Fe²⁺ and Ni²⁺ formate dihydrates were measured. Fe²⁺ salt showed a sharp peak at T_N=3.75±0.05 K with total magnetic entropy Nk⁄2(ln5+ln2). Ni²⁺ salt exhibited a distinct peak at T_N=15.5±0.2 K and a Schottky type maximum around 3.1 K. It was discussed that M²⁺ ions in (200) layer in this series of compounds were magnetically free and that M²⁺ ions in (100) layer behaved as magnetically two-dimensional spin system which ordered at T_N. It was concluded theoretically, using R. P. A. method, that the broad shoulder generally found in the specific heat curve just above T_N was characteristic to the low dimensional spin system. This tendency was remarkable in the system with isotropic coupling such as Mn²⁺ ions and not so distinct in the case of anisotropic Co²⁺ ions. The present cases of Fe²⁺ and Ni²⁺ ions gave the examples of those with intermediate anisotropy.

View full abstract

The nuclear spin-lattice relaxation times T₁ for Mn⁵⁵, Sb¹²¹ and Sb¹²³ in ferromagnetic intermetallic compound MnNiSb have been measured in applied magnetic field above 6 kOe in the temperature range between 4.2 and 600 K.
Below 250 K the relaxation rates T₁⁻¹ for the three nuclei are proportional to the temperature T, while above 250 K they are expressed as T₁⁻¹=aT+bT^3.8±0.2, where T₁ is in unit of second, and a=2.9, 2.5 and 0.74 for Mn⁵⁵, Sb¹²¹ and Sb¹²³, respectively, and b=8.1×10⁻⁸, 7.7×10⁻⁸, 2.3×10⁻⁸ for Mn⁵⁵, Sb¹²¹ and Sb¹²³, respectively. The relaxation is mainly due to the interaction between the nuclear spins and conduction electrons via spin waves at low temperatures, and due to the three magnon process at high temperatures.

View full abstract

Magnetic measurements were made of the systems (Cr_1.01Sb)_1−x(Fe_1.22Sb)_x and (Cr_1.01Sb)_1−x(Co_1.13Sb)_x. In both systems, ferromagnetism appeared in the intermediate range of x. In the (Cr, Fe)Sb system maximum of the spontaneous magnetization and the Curie temperature was found at x=0.6. However, the temperature variation of the magnetization near the Curie temperature was not so sharp as in the usual ferromagnet, and also the high field susceptibility at low temperatures was anomalously high. X-ray and neutron diffraction measurements revealed that there was no miscibility gap between ferromagnetic and antiferromagnetic phases. Mössbauer effect showed that, for x=0.8 the internal field on Fe⁵⁷ nuclei was about 90 kOe, and the isomer shift (against stainless steel) was 0.54 mm/sec. The anomalous behavior of magnetization was even more pronounced in the (Cr, Co)Sb system. Ferromagnetic interactions Cr–Sb–Fe and Cr–Sb–Co can well be interpreted on the basis of the Goodenough-Kanamori theory.

View full abstract

A method is presented to determine the variation of superconducting transition temperature for tin. The initial linear drop of T_c when plotted against change in volume, which is experimentally observed fact, is theoretically confirmed.

View full abstract

Yield stress of Cu and Cu base solid solutions is measured from room temperature down to 1.6 K. Two kinds of anomalous behavior of the yield stress of the solid solutions are observed below 50 and 10 K. From theoretical considerations, these anomalies are attributed to dynamical motion of dislocation and to dynamical production of point defects due to climb motion of the dislocation, respectively. Hysteresis behavior of the temperature dependence of the yield stress, which is due to the dynamically produced point defects, is observed in very low temperature region. Criterion for applicability of chemical rate process to the motion of dislocation is discussed.

View full abstract

In the nuclear quadrupole resonance spectra there is only one weak absorption peak in Sn Cl₂2H₂O, and two peaks in K₂SnCl₄H₂O - one strong and the other weak. These observations indicate that two chlorines in SnCl₂(OH₂) complex are in almost identical positions. In (SnCl₃)⁻ ion, on the other hand, there are two non-equivalent positions for chlorine atoms.
The dependence of nuclear quadrupole resonance frequency on temperature is assumed to arise from relative angular displacements (θ) of covalently bonded atoms. Major contribution is found to come from two orthogonal lattice modes each of wave number 39 cm⁻¹.

View full abstract

Cu²⁺ in NaCl, LiCl and NaF, and Ni⁺ in NaCl, most of which were produced from Cu⁺ and Ni²⁺ by X-ray irradiation were studied by the e.s.r.
All of Cu²⁺ had elongated tetragonal surroundings, while Ni⁺ had compressed ones. In NaCl:Cu²⁺, the optical dichroism along a cube edge was detected at 5 K corresponding to the Jahn-Teller distortion.
From the observed super hyperfine structure of surrounding nuclei the amounts of covalency, f_s and f_σ were estimated as 0.77 to 0.89% and 7.9 to 12% in the chlorides, respectively.
In the case of NaCl:Cu²⁺ doped as divalent states, sharp anisotropic spectra without the hyperfine structure due to Cu nucleus were observed, which are presumably due to coagulated ions.

View full abstract

Absorption spectra of thin films of all rubidium halides are investigated at room an liquid nitrogen temperatures in the energy range 12–30 eV. Synchrotron orbital radiation at INS-Tokyo was used as a continuum light source. Several sharp peaks are found in the range 16–19 eV. When samples are cooled to liquid nitrogen temperature, two of them shift towards high energy, while three of them towards low energy. The former are attributed to the excitons composed of Rb+4p hole and the s-like electron, while the latter are attributed to those composed of Rb+4p hole and the d-like electron. The multiplicity of the exciton peaks is discussed in terms of the band model and the atomic model.

View full abstract

The electron spin resonance experiment was performed on phosphorus donors in compensated n-type silicon in the temperature range of 1.5 K to 4.2 K, using the microwave of 46 GHz. From the comparison of the peak shifts of the central lines in highly compensated samples and in uncompensated ones, the average local density of donor electrons were obtained in highly compensated samples, whose magnitude was rather close to N_D than N_D−N_A. This result is interpreted in terms of a simple model that the donor electrons are mostly located outside the critical spheres centred at each negatively charged acceptor as a result of Coulomb repulsion between the donor electrons and the charged acceptors, as first considered by Mott and Davis. The temperature dependence of the peak shift of the central line and the line broadening are also discussed.

View full abstract

The temperature dependence of the decay time of singlet excitons in anthracene crystals was measured under no suffering of reabsorption effect. It was clarified that the excitons were populated on the two Davydov states in quasi-thermal equilibrium before emission process. Furthermore, probabilities of energy transfer from the exciton to doped acceptors were measured and the values of the diffusion coefficient D of the exciton was estimated as 10⁻¹∼1 cm²/sec which was much larger than that obtained by many researchs. A similar measurement to that by Simpson was carried out by using a pure perylene film instead of the tetracene doped film in the earlier measurement, giving D as 1.5 cm² sec⁻¹. Furthermore, the drift time due to the diffusion of the exciton through a thin anthracene layer was directly observed, giving D as 1.3 cm² sec⁻¹.

View full abstract

A method to calculate the “abnormal” stopping power of the planar channeled particle in crystal is proposed. Making use of the formula and Bohr’s classical model the abnormal stopping power is calculated as a function of the distance from the channeling wall for electronic and nuclear excitations.

View full abstract

Precipitation of hydride from the solid solution of vanadium-hydrogen containing a small amount of hydrogen was observed at temperatures ranging between 300 K and 77 K using the cold stage of a 500 kV electron microscope. Two types of precipitates were found at low temperatures. One has a cubic superstructure with a unit cell twice as large as that of vanadsum matrix. The other has a tetragonal structure in which vanadium atoms form a body-centered tetragonal lattice with c⁄a=1.1−1.3. On heating these precipitates dissolved to the matrix at certain temperatures depending on the hydrogen concentration of the specimens. These facts give a direct confirmation to the postulation that the ‘anomalies’ in vanadium metal are caused by the precipitation as the hydride phase of a trace of hydrogen involved.

View full abstract

The experimental observations on the two X-ray wave fields in elastically distorted silicon single crystals, which were reported in Part I (J. Phys. Soc. Japan 31 (1971) 204), are analysed on the basis of the dynamical diffraction theory. A new technique for computer calculation of propagation paths, phase changes and intensities of the wave-field beams in a distorted crystal is devised. Satisfactory agreements are obtained between experiment and theory for a uniformly curved crystal and a crystal compressed with knife edges. A physical interpretation is given on the asymmetry of the diffraction intensities of the two wave fields with respect to the sign of elastic strain gradient.

View full abstract

The dynamical theory of electron and X-ray diffraction for a deformed crystal, developed by Takagi, is studied in a finite crystal which includes both the Laue case and the Bragg case by the way on incidence. The integral representations of the crystal wave in a deformed crystal are expressed by the Green functions in a perfect crystal. The diffracted wave in a deformed crystal is given by the sum of the wave field in a perfect crystal and that in a deformed region. The general expressions of the Pendellösung fringes reflected by the interface of the crystal are obtained, and it is shown that there is no essential difference between the Laue case and the Bragg case. The experimental results of reflected Pendellösung fringes by the crystal sides are reported in the X-ray case.

View full abstract

The Non-Gaussian corrections have been estimated for liquid argon by using a model in which the motion of a typical atom is analyzed in terms of the dynamics of an “oscillation”, a quasiparticle consisting of the atom plus a surrounding spherical shell representing the collective effect of the instantaneous near neighbours. Tne oscillatory motion of the atom inside the shell is represented by a stochastic Langevin oscillator first used by Rahman, Singwi and Sjolander. As regards the diffusive motion of the atom plus the spherical shell, a Langevin binary collision model is used. Comparison with Rahman’s calculations for liquid argon shows that the agreement of velocity autocorrelation and α₂(t) has been considerably improved with the present model in comparison with the earlier Gibbs model.

View full abstract

Anomalous enhancement of a transmitted X-ray beam in Bragg-case diffraction is studied experimentally for the case that the direction of the diffracted beam comes close to the entrance surface of a target crystal. The intensity of the transmitted ray at μ₀t=10 amounts to 30% of the incident beam, which is extremely stronger in comparison with observations up to the present. In this experiment (220)CrK_α1 diffraction from a silicon single crystal is used in the double crystal spectrometer arrangement. Theoretical explanation for the phenomenon is also tried with a method which is more rigorous than the conventional two-waves approximation. A fairly good agreement is obtained between the experimental and theoretical results both for the anomalously transmitted intensity, and for the difference of the incident angle at which the intensities of the anomalously transmitted and diffracted beams reach to a maximum respectively.

View full abstract

Transverse relaxation time of optically pumped cesium atoms in the ground state has been measured by use of the technique of multiple spin echo and cross-beam. Longitudinal relaxation time has also been measured by use of the pulse technique. The variation of relaxation time with the buffer gas pressure and the cell temperature has been studied in an unlined glass cell. Transverse relaxation time (T₂)_F+ depends strongly on the cell temperature but longitudinal relaxation time T_n does not. From the temperature dependence of (T₂)_F+, the spin-exchange cross section has been evaluated as 1.4×10⁻¹⁴ cm². Disorientation cross sections have been evaluated as follows: σ((T₂)_F+)=1.8×10⁻²³ cm² and σ(T_n)=3.2×10⁻²⁴ cm² for cesium-neon collisions; σ((T₂)_F+)=5.9×10⁻²² cm² and σ(T_n)=2.5×10⁻²³ cm² for cesium-argon collisions. Diffusion coefficients for cesium in neon and in argon have been evaluated as 0.19 cm²/sec and 0.14 cm²/sec, respectively. For the interrelation of transverse and longitudinal relaxation times, it is revealed that (1⁄T_e+1⁄T_n) is equal to (1⁄(T₂)_F++1⁄(T₂)_F−) in the case of extreme motion narrowing.

View full abstract

A theory is given to compute the shift of equilibrium nuclear distance of molecule in every electronic state from initially assumed value, in terms of electron-vibration interaction. It is applied to the computation of the equilibrium nuclear distances of the ground, the first and the second singlet excited states of a naphthalene molecule. The calculated relative shifts of the equilibrium point of vibration (corresponding roughly to that of nuclear distance) between the ground and the first and the second singlet excited states are, in average, 3.3×10⁻² Å and 7.1×10⁻² Å respectively. The equilibrium nuclear distances of the molecule are also obtained with LCAO-ASMO-INDO-CI method. The shifts of equilibrium nuclear distances by this method between the ground and the first and the second singlet excited states are 0.5×10⁻² Å and 0.8×10⁻² Å respectively. The values calculated by the two methods are in reasonable agreement.

View full abstract

Total ionization cross sections of Ca, Sr and Ba by electron impact have been measured by the crossed beam technique. Intensity of neutral atomic beam is determined by the deposition method. Sample atoms deposited onto a beam collector are quantitatively analyzed by atomic absorption spectrophotometry. The absolute cross sections are determined to be 6.2±0.2 Ų at 13.6 eV for Ca and 7.2±0.3 Ų at 12.6 eV for Sr. The absolute cross section of Ba could not be determined because of a poor sensitivity of spectrophotometer for Ba. Possible systematic errors are estimated to be between +8% and −19% for both of Ca and Sr. Relative cross sections of the three elements are obtained for electron energy from 0 eV to 1000 eV. Each curve for the total ionization cross section as a function of electron energy has two maxima in low energy region, one of which is considered to be due to autoionization. The results are compared with some experimental results and theoretical calculations by other workers.

View full abstract

The electron-transfer from the reduced form NAD_red of NAD (nicotinamide adenine dinucleotide) to FMN (flavin mononucleotide), which plays an important role in biological energy-transformations, is studied according to the Mulliken theory for charge-transfer complexes. The π-electronic structures of NAD and FMN are determined in terms of the Pariser-Parr-Pople approximation of LCAO-ASMO-SCF theory. The geometrical configuration of NAD-FMN complex is assumed such that the molecular plane of pyridine ring of NAD is parallel to that of isoalloxazine ring of FMN, in order to obtain an optimum overlap of π-electrons between them. It is shown that the electron-transfer does not occur from NAD_red to FMN but only from the ionized form (NAD_ox)²⁻ to FMN (NAD_ox being the oxidized form of NAD).

View full abstract

Orientation of poly-γ-benzyl-L-glutamate under magnetic field has been measured in liquid-crystalline solution and in film, cast and dried from the solution, by means of optical and electrostatic methods. The orientation which is in the direction of the external field is of an antiparallel type and proposed to be due to induced magnetic dipoles of the side chain groups of the polypeptide molecules. Although the orientation is poor in solution, it is striking in film, and some cooperative behavior of the permanent electric dipoles in a system of the molecular clusters of the polypeptide and of the solvent molecules, which becomes especially prominent as the solution is dried up, is suggested to be involved. Some wall effects from the surfaces of the optical cell used, however, make it difficult of detect true magnetic orientation in solution.

View full abstract

Ultrasonic absorption measurements have been conducted in heavy water-dioxane mixtures over the entire composition range at six different frequencies in the range 30–100 Mc/s and at 25°C, using pulse technique. The nature of the α⁄f² versus X_HW (mole fraction of heavy water) curve is found to be quite similar to that observed for water-dioxane mixtures. The results have been analysed in terms of a two-relaxation mechanism proposed by Hammes and Knoche.

View full abstract

The equilibrium of the current-carrying toroidal plasma in the Heliotron C field is studied experimentally. The equilibrium state is very sensitive to a change in the transverse field of order 10⁻³ of the main confining field. The effect of vertical magnetic field on the equilibrium is precisely examined by measuring the electrostatic equipotential surface of the plasma and the apparent electric conductivity of the plasma current. The observed values of the optimum vertical field B_v, which is necessary for the equilibrium of a current-carrying toroidal plasma, are about 1⁄2∼1⁄3 of the theoretical values.

View full abstract

The characteristics of double probes immersed in plasmas in which electrons and ions have drifted Maxwellian distributions are theoretically investigated by using an electronic computer. The results about a double probe which has “two frontal electrodes” show that the electron drift changes the inclination of the characteristic curve; therefore, the electron temperature estimated from the curve contains an appreciable error. On the contrary, the results about a probe which has “back-to-back electrodes” show that the electron drift shifts the idealized characteristic curve parallel to the potential axis of the figure and the ion drift parallel to the current axis, but the original pattern is still conserved; therefore, the estimated temperature is valid in this case as far as the drift velocity of electrons or ions is far lower than their thermal velocity.

View full abstract

The δ∫dl(1/B) criterion of the plasma stability is extended to the relativistic plasma. The relativistic plasma is stable for the interchange instability if
(Remark: Graphics omitted.)
where Π_⁄⁄ and Π_⊥ are the anisotropic pressure of the relativistic plasma along and perpendicular to the magnetic line of force respectively.

View full abstract

The relaxation rate is obtained on the basis of the unified theory. When the ion temperature is of the same order of magnitude as the electron temperature, the effective screening length of the interaction is the electron Debye length. As the ion temperature decreases, the effective screening length decreases. The low ion-temperature asymptote is obtained. Numerical values are given graphically.

View full abstract

The combination of the toroidal h.f. electric field and the stellarators with stellarator winding located on the major radius side is exhibited to be a possible stationary fusion reactor. The fusion ignition condition is attainable by the major radius compression of toroidal plasma.

View full abstract

The coulomb logarithm for the viscosity coefficient of a plasma in a magnetic field is determined exactly by the quantum mechanical unified theory. The magnetic field is assumed so strong that the condition,
Debyelength << ion gyration radius << mean free path,
is satisfied. For a hydrogenic plasma, the quantum correction to the coulomb logarithm can not be neglected if the temperature is higher than 10⁶ K.

View full abstract

Effect of inhomogeneity in plasma density and magnetic field on the propagation of magneto-acoustic waves in a cold collision-free plasma is investigated. It is shown, by using a nonlinear perturbation method, that the basic system of equations governing one-dimensional plane waves with small but finite amplitude can be reduced to a modified form of the Korteweg-de Vries equation, from which we can expect damping, growing or splitting of the waves.

View full abstract

A circular magnetic field is applied to the channel. The fluid is inviscid and thermally nonconductive. The electrical conductivity of the fluid is assumed to be small so that the distorsion of the magnetic field is neglected. The basic equations are linearized and the solution is obtained by the method of Fourier transforms. The solutions consist of two parts, including the three parameters, the Mach number, the interaction parameter and the interval between the walls. One part comes from the interaction between the fluid and the magnetic field. The other is the interaction between the fluid and walls. The flow accelerates in the channel for subsonic case. This fact indicates that the effect of the Joule heating overcomes the Lorentz force in the case of channel flow across the nonuniform magnetic field.

View full abstract

The hydromagnetic flow due to the impulsive rotation of an infinite disc has been studied. The equations of the problem have been linearised by expanding the velocity components, pressure and the magnetic field components in powers of the dimensionless angular rotation of the disc. It is observed that velocity components are reduced by the increase of the magnetic field. The induced magnetic field components are of the order of the magnetic Prandtl number and is small for practical fluids. The boundary layer displacement thickness is decreased by the increase of the applied magnetic field.

View full abstract

Time-dependent flows around circular cylinders and flat plates, which are decelerated from a steady speed, were investigated by means of a flow visualization technique at low Reynolds numbers.
For very small values of deceleration, the twin-vortices behind the test body shorten monotonically during deceleration, but elongate rapidly just before the test body is stopped. For intermediate values of deceleration, the twin-vortices elongate slightly at the first, but after a while they begin to shorten, the elongate again just before the test body is completely stopped. For large values of deceleration, the twin-vortices elongate monotonically.
When the test body is decelerated rapidly from one steady speed to another lower speed, a large vortex-pair is formed in the wake during deceleration. After the second speed is reached the vortex-pair leaves the test body and moves backward, and the whole field of flow proceeds to grow into a new steady state.

View full abstract