Metastability of diamond ramp-compressed to 2 terapascals.

Carbon is the fourth-most prevalent element in the Universe and essential for all known life. In the elemental form it is found in multiple allotropes, including graphite, diamond and fullerenes, and it has long been predicted that even more structures can exist at pressures greater than those at Earth's core1-3. Several phases have been predicted to exist in the multi-terapascal regime, which is important for accurate modelling of the interiors of carbon-rich exoplanets4,5. By compressing solid carbon to 2 terapascals (20 million atmospheres; more than five times the pressure at Earth's core) using ramp-shaped laser pulses and simultaneously measuring nanosecond-duration time-resolved X-ray diffraction, we found that solid carbon retains the diamond structure far beyond its regime of predicted stability. The results confirm predictions that the strength of the tetrahedral molecular orbital bonds in diamond persists under enormous pressure, resulting in large energy barriers that hinder conversion to more-stable high-pressure allotropes1,2, just as graphite formation from metastable diamond is kinetically hindered at atmospheric pressure. This work nearly doubles the highest pressure at which X-ray diffraction has been recorded on any material.

Probing the Solid Phase of Noble Metal Copper at Terapascal Conditions.

Ramp compression along a low-temperature adiabat offers a unique avenue to explore the physical properties of materials at the highest densities of their solid form, a region inaccessible by single shock compression. Using the National Ignition Facility and OMEGA laser facilities, copper samples were ramp compressed to peak pressures of 2.30 TPa and densities of nearly 30 g/cc, providing fundamental information regarding the compressibility and phase of copper at pressures more than 5 times greater than previously explored. Through x-ray diffraction measurements, we find that the ambient face-centered-cubic structure is preserved up to 1.15 TPa. The ramp compression equation-of-state measurements shows that there are no discontinuities in sound velocities up to 2.30 TPa, suggesting this phase is likely stable up to the peak pressures measured, as predicted by first-principal calculations. The high precision of these quasiabsolute measurements enables us to provide essential benchmarks for advanced computational studies on the behavior of dense monoatomic materials under extreme conditions that constitute a stringent test for solid-state quantum theory. We find that both density-functional theory and the stabilized jellium model, which assumes that the ionic structure can be replaced by an ionic charge distribution by constant positive-charge background, reproduces our data well. Further, our data could serve to establish new international secondary scales of pressure in the terapascal range that is becoming experimentally accessible with advanced static and dynamic compression techniques.

Ramp compression of diamond to five terapascals.

The recent discovery of more than a thousand planets outside our Solar System, together with the significant push to achieve inertially confined fusion in the laboratory, has prompted a renewed interest in how dense matter behaves at millions to billions of atmospheres of pressure. The theoretical description of such electron-degenerate matter has matured since the early quantum statistical model of Thomas and Fermi, and now suggests that new complexities can emerge at pressures where core electrons (not only valence electrons) influence the structure and bonding of matter. Recent developments in shock-free dynamic (ramp) compression now allow laboratory access to this dense matter regime. Here we describe ramp-compression measurements for diamond, achieving 3.7-fold compression at a peak pressure of 5 terapascals (equivalent to 50 million atmospheres). These equation-of-state data can now be compared to first-principles density functional calculations and theories long used to describe matter present in the interiors of giant planets, in stars, and in inertial-confinement fusion experiments. Our data also provide new constraints on mass-radius relationships for carbon-rich planets.

X-Ray Diffraction of Solid Tin to 1.2 TPa.

We report direct in situ measurements of the crystal structure of tin between 0.12 and 1.2 TPa, the highest stress at which a crystal structure has ever been observed. Using angle-dispersive powder x-ray diffraction, we find that dynamically compressed Sn transforms to the body-centered-cubic (bcc) structure previously identified by ambient-temperature quasistatic-compression studies and by zero-kelvin density-functional theory predictions between 0.06 and 0.16 TPa. However, we observe no evidence for the hexagonal close-packed (hcp) phase found by those studies to be stable above 0.16 TPa. Instead, our results are consistent with bcc up to 1.2 TPa. We conjecture that at high temperature bcc is stabilized relative to hcp due to differences in vibrational free energy.

Time-resolved X-ray diffraction diagnostic development for the National Ignition Facility.

We present the development of an experimental platform that can collect four frames of x-ray diffraction data along a single line of sight during laser-driven, dynamic-compression experiments at the National Ignition Facility. The platform is comprised of a diagnostic imager built around ultrafast sensors with a 2-ns integration time, a custom target assembly that serves also to shield the imager, and a 10-ns duration, quasi-monochromatic x-ray source produced by laser-generated plasma. We demonstrate the performance with diffraction data for Pb ramp compressed to 150 GPa and illuminated by a Ge x-ray source that produces ∼7 × 1011, 10.25-keV photons/ns at the 400 µm diameter sample.

Solid iron compressed up to 560 GPa.

Dynamic compression by multiple shocks is used to compress iron up to 560 GPa (5.6 Mbar), the highest solid-state pressure yet attained for iron in the laboratory. Extended x-ray absorption fine structure (EXAFS) spectroscopy offers simultaneous density, temperature, and local-structure measurements for the compressed iron. The data show that the close-packed structure of iron is stable up to 560 GPa, the temperature at peak compression is significantly higher than expected from pure compressive work, and the dynamic strength of iron is many times greater than the static strength based on lower pressure data. The results provide the first constraint on the melting line of iron above 400 GPa.

Extended X-ray absorption fine structure of dynamically-compressed copper up to 1 terapascal.

Large laser facilities have recently enabled material characterization at the pressures of Earth and Super-Earth cores. However, the temperature of the compressed materials has been largely unknown, or solely relied on models and simulations, due to lack of diagnostics under these challenging conditions. Here, we report on temperature, density, pressure, and local structure of copper determined from extended x-ray absorption fine structure and velocimetry up to 1 Terapascal. These results nearly double the highest pressure at which extended x-ray absorption fine structure has been reported in any material. In this work, the copper temperature is unexpectedly found to be much higher than predicted when adjacent to diamond layer(s), demonstrating the important influence of the sample environment on the thermal state of materials; this effect may introduce additional temperature uncertainties in some previous experiments using diamond and provides new guidance for future experimental design.

Establishing gold and platinum standards to 1 terapascal using shockless compression.

New techniques are advancing the frontier of high-pressure physics beyond 1 terapascal, leading to new discoveries and offering stringent tests for condensed-matter theory and advanced numerical methods. However, the ability to absolutely determine the pressure state remains challenging, and well-calibrated pressure-density reference materials are required. We conducted shockless dynamic compression experiments at the National Ignition Facility and the Z machine to obtain quasi-absolute, high-precision, pressure-density equation-of-state data for gold and platinum. We derived two experimentally constrained pressure standards to terapascal conditions. Establishing accurate experimental determinations of extreme pressure will facilitate better connections between experiments and theory, paving the way toward improving our understanding of material response to these extreme conditions.

Cross-stimulation of monoclonal antibodies in anamnestic responses.

Immunization of BALB/c mice with Group A streptococcal vaccines leads to the induction of high levels of monoclonal antibody populations. Subsequent immunization of these mice with Group A-variant streptococcal vaccines induces a significant level of monoclonal antibody of A-variant antigen specificity revealed by labeled group A-variant polysaccharide. During these course Av and Av' immunizations, the monoclonal Group A-specific antibodies were also restimulated to levels usually higher than the variant-specific antibodies. With two exceptions, these homogeneous antibody populations were not cross-reactive in vitro with the related antigen. Such cross-stimulation of monoclonal antibodies was interpreted as a function of particular membrane properties of the Ig receptor-bearing memory cells which, for restimulation, would only require the structurally closely related antigen which serves as a backbone to the original antigen, and not necessarily the exact fit of the homologous immunodominant group.

Genetics of restricted antibodies to streptococcal group polysaccharides in mice. I. Strain differences of isoelectric focusing spectra of group A hyperimmune antisera.

The immune response of nine inbred and one outbred strain of mice to the streptococcal group A polysaccharide was investigated with respect to magnitude and restriction. Analytical isoelectric focusing served as a tool to estimate the degree of restriction of Group A polysaccharide-specific antibodies. It proved feasible to distinguish low and intermediate from high responder strains, and to delineate strain-specificity of isoelectric focusing spectra of the immune sera. For example, immune sera of BALB/c mice, restricted high responders, and of C57BL/6 mice, heterogeneous low responders, had distinct focusing properties. Responsiveness was a dominant autosomal genetic trait in C57BL/6 x BALB/c F(1) hybrid mice, irrespective of the maternal and the paternal genotype; the immune sera of these mice had their own, rather uniform isoelectric focusing spectra whereby structural genes of the low responder strain were expressed to predominant levels in 81% of the hybrids. Responsiveness in C57BL/6 x BALB/c F(2) progeny segregated into 79% high and 21% low responders, and showed no genetic linkage to the following characteristics: hair color, sex, H-2 type, and Ig allotype of the heavy chain. The isoelectric focusing properties of these immune sera indicated segregation into patterns like BALB/c mice (40%), F(1) hybrids (48%), and C57BL/6 mice (12%). Since this segregation is independent of any of the above criteria in these F(2) mice a regulatory gene(s) is postulated that controls the clonal pattern of the immune response.

The individual antigenic specificity of antibodies to streptococcal carbohydrates.

Although a single electrophoretically uniform antibody component with specificity for the group carbohydrate may comprise the bulk of the gamma-globulin in rabbits immunized with streptococcal vaccines, this is not always the case. Not infrequently, electrophoresis may reveal multiple antibody components. Nevertheless, it has been feasible by various preparative procedures to isolate from a single antiserum at least two antibody components with similar reactivity for the carbohydrate both of which are electrophoretically monodisperse. Light chains from such antibodies reveal a restricted pattern when examined by disc electrophoresis. Antibodies to streptococcal carbohydrates have been examined for their individual antigenic specificity. Goats were immunized with isolated Group C and Group A-variant antibodies raised in rabbits. Individual antigenic specificity of these antibodies was brought out by absorption of the goat anti-antiserum with Fr II of pooled normal rabbit sera. Additional absorption of the goat anti-antisera with Fr II diminished but did not eliminate the reactivity for the homologous antibody. Immunoelectrophoretic studies with papain fragments of purified streptococcal antibodies localized the specificity to the Fab fragment. Specificity was not confined to the isolated light chains of the antibody.

Rabbit antibodies to streptococcal carbohydrates. Influence of primary and secondary immunization and of possible genetic factors on the antibody response.

In a search for possible genetic factors which may influence the immune response to the streptococcal carbohydrates, over 100 rabbits have been immunized with streptococcal vaccines, and representative examples of high and low response pairs mated. The concentration of precipitins to the group-specific carbohydrates has been measured in the antisera following primary intravenous immunization with heat-killed streptococcal vaccines, Group A, Group A-variant, and Group C. For the majority of rabbits, the concentration of precipitins varied between 1 and 10 mg/ml of antiserum; while in the minority, it was between 11 and 32 mg/ml. The offspring of rabbits with high antibody levels had a significantly higher concentration of antibody than was seen in the offspring of rabbits of low response parents. Such data suggest that the magnitude of the immune response to these carbohydrate antigens is under some form of genetic control. Not uncommonly in rabbits with hyper-gamma-globulinemia following primary immunization, the group-specific precipitins are the predominant component of the gamma-globulin. An unusual feature of such components is that they are electrophoretically monodisperse, and possess individual antigenic specificity. In this respect they resemble the myeloma proteins. When a response of this sort is not seen after primary immunization, it may occur after secondary immunization. Therefore, prior exposure to the same or closely related antigen may also have an influence on the occurrence of high concentrations of such uniform antibodies.

Idiotypic specificity of rabbit antibodies to streptococcal group polysaccharides.

Anti-idiotypic antisera against six restricted rabbit streptococcal group specific antibodies have been raised in rabbits matched for allotypes. All these antisera reacted specifically with their homologous idiotypes on double-diffusion tests in agarose gel. In addition, they showed a high incidence of cross-specificities with group-specific hyperimmune sera induced in both closely related and unrelated individuals. These precipitating cross-specificities could be explained for two systems by the interference of rheumatoid factor. Two idiotypic antibody systems have been analyzed in detail; these were restricted antibodies produced in a father and in one of his offspring. The methods employed included binding inhibition of radio-labeled homologous Fab fragments and hemagglutination inhibition with homologous idiotypic coat. The data demonstrated that only related rabbits produced, besides non-cross-reacting antibodies, idiotypically similar antibodies raised to the same antigen. About one-third of the cross-reactive idiotypes showed binding inhibition between 31 and 92%. Inhibition of binding above 50% in the paternal idiotypic system was only achieved by one offspring antibody whereas the F(1) progeny idiotypic system was inhibited to this extent by seven antibodies of related rabbits. In contrast, 87.5% and 91.7% of antibodies of unrelated rabbits were less than 20% inhibitory. Within this study two idiotypically identical antibodies have not been found. This implies that A-variant-specific antibodies of related rabbits which produced antipolysaccharide antibodies were structurally different. Cross-reaction, even if greater than 90% by binding inhibition, appears to involve only part and not all of the variable regions.

Influence of genetic factors on the magnitude and the heterogeneity of the immune response in the rabbit.

Selective breeding of rabbits immunized with Group C and Group A streptococcal vaccines was employed to reveal genetic influences on the magnitude and on the restriction in heterogeneity of the immune response to the group-specific carbohydrates. After two generations of selective breeding, complete segregation was achieved between a high-response population (>18 mg precipitins/ml serum, average 33 mg/ml) and a low-response population (<13 mg precipitins/ml serum, average 7.5 mg/ml) to Group C carbohydrate. This suggests that a limited number of genes controls the magnitude of the immune response to this antigen. Selective breeding of rabbits which were representative of heterogeneous, restricted, and monoclonal responses revealed that the degree of antibody heterogeneity in the parental rabbits is reflected in the offspring. More than 95% of the offspring derived from rabbits which had a heterogeneous immune response developed heterogeneous antibodies. 33% of the offspring derived from rabbits which had restricted and monoclonal immune responses developed monoclonal antibodies. This suggests that the degree of heterogeneity of the antibody response to the streptococcal carbohydrates is under genetic control. The degree of heterogeneity and the magnitude of the immune response appear to be independent variables.

A rabbit family of restricted high responders to the streptococcal group A-variant polysaccharide. Selective breeding narrows the isoelectric focusing spectra of dominant clones.

Immunization of rabbits from a closed colony with streptococcal Group A-variant vaccines identified about two-thirds of them as low and heterogeneous responders. One-third of the rabbits showed a restriction of the response independent from the magnitude. Selective breeding from one monoclonal high-responder male and two restricted high-responder female rabbits succeeded in segregation of high-responder progeny after two generations. Their antibody levels were on the average 2.5 times higher than those of the random group of rabbits and a small group of low-responder offspring. Immunization of 13 offspring originating from rabbits bred for restricted high response to the streptococcal Group C polysaccharide revealed that 11 progeny were restricted high responders and 2 progeny monoclonal high responders. This finding suggests that high responsiveness to the Groups A-variant and C polysaccharides is inherited as genetically linked traits. Selective breeding combinations between restricted and monoclonal high-responder rabbits by brother-sister matings succeeded in narrowing the isoelectric focusing spectra of Group A-variant-specific antibodies in the offspring. It furthermore revealed a preferential expression of monoclonal antibodies after three generations with a similar net charge as those identified first in the original monoclonal paternal parent. These data suggest that similar copies of structural genes for the variable regions are transmitted from the parent to the progeny.

Antibody response to the streptococcal group A-variant polysaccharide in BASILEA rabbits lacking kappa-polypeptide chains.

Rabbits from a variant strain called BASILEA, in which homozygotes express only lambda-type chains and heterozygotes have normal kappa/lambda ratios, were hyperimmunized with a streptococcal group A variant vaccine. Homozygotes (bas/bas) produced antibodies with lambda-chains, heterozygotes, however, produced predominantly antibodies with kappa-chains. The incidence of restricted high responders in the BASILEA strain was high; it was probably introduced by the original mutant rather than by the loss of kappa-chains (founder effect). The degree of heterogeneity of homozygotes is similar to the heterogeneity of heterozygotes, and to that of rabbits expressing kappa-chains. This suggests that in the rabbit, the repertoire of lambda-chain genes is of similar size to that of kappa-chain genes.

Distinct functions of monoclonal IgG antibody depend on antigen-site specificities.

Intraveneous hyperimmunization of selectivity bred rabbits with streptococcal group A-variant vaccines elicits antibody responses of restricted heterogeneity at high antibody levels. All antisera contain two functionally distinct antibody populations, which can be isolated in single-band purity upon analytical isoelectric focusing. Typical examples of these two kinds of single-band antibodies were investigated in great detail for several parameters by a variety of methods. 85--99% of the streptococcal group A-variant polysaccharide (Av-CHO)-specific antibody in the antisera does not precipitate the isolated 5,000 daltons poly-L-rhamnose antigen, neither agglutinates nor lyses in the presence of complement Av-CHO-coated sheep erythrocytes (SRBC), binds the radio-labeled Av-CHO with an association constant in the ragne of 10(5)--10(6) M-1, and is of terminal specificity (nonreducing end) for the linear Av-CHO. In contrast, the minor fraction of Av-CHO-specific antibody (1--15%) does precipitate the linear Av-CHO, both agglutinates and lyses Av-CHO-coated SRBC in the presence of complement, has an affinity range of 10(8)--10(9) M-1, and is of internal specificity for the Av-CHO. The antigenic determinants of the Av-CHO for the antibodies are nonoverlapping, only one Fab of the low affinity antibody can be bound whereas four Fab of the high affinity antibody are accommodated. Hence, the determinant specificity explains the functional differences observed, for there is no indication of subclass differences. A mechanistic model of the A-variant carbohydrate presentation on the vaccine appears to account best for the unbalanced levels of low and high affinity antibody.

Immunochemical studies on the cross-reactivity between streptococcal and staphylococcal mucopeptide.

Particulate mucopeptides of Group A-variant streptococci and Staphylococcus aureus, solubilized by ultrasonic treatment, give a precipitin reaction with the sera of rabbits immunized with Group A-variant streptococci. gamma-G globulin antibodies have been recovered from these sera which react with the mucopeptides but not with the Group A-variant carbohydrate. The immunochemical basis for the cross-reactivity between the streptococcal and staphylococcal mucopeptides was investigated in detail. Three chemically different fractions have been isolated from enzymatic digests of staphylococcal mucopeptide and were employed as haptenic inhibitors of the precipitin reaction. A fraction consisting of the peptide moiety of mucopeptide was the strongest inhibitor, whereas the hexosamine-rich fraction was less effective. The third fraction, rich in glycine, was least effective. It is suggested that the immunologic cross-reactivity between streptococcal and staphylococcal mucopeptide is due to the fact that these two substances contain chemically similar tetrapeptides. The hexosamine polymer which is identical for both mucopeptides may also contribute to their cross-reactivity.

The emergence of antibodies with either identical or unrelated individual antigenic specificity during repeated immunizations with streptococcal vaccines.

Electrophoretically monodisperse antibody components in rabbit antisera to the carbohydrates of the Groups A and C streptococci have been examined for their individual antigenic specificity. In these antibody components which were isolated by preparative electrophoresis, individual antigenic specificity was confined to the specific antibody and was absent in the nonantibody gamma-globulin. Radioprecipitation experiments and the use of immune absorbent columns constructed from goat anti-antisera, which had been absorbed with fraction II, revealed that all the specific antibody in an electrophoretically monodisperse component was reactive with the homologous anti-antibody. Antibodies with either identical or distinct individual antigenic specificities may occur in the same rabbit with repeated immunizations. Antibodies with identical antigenic specificity had identical electrophoretic mobility, whereas antibodies with unrelated antigenic specificities had distinct electrophoretic mobilities. In the interval between immunizations, if antibody to the carbohydrate antigen was absent, there was no detectable antibody with individual antigenic specificity.