Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Ultrafast time-resolved 2D imaging of laser-driven fast electron transport in solid density matter using an x-ray free electron laser

High-power, short-pulse laser-driven fast electrons can rapidly heat and ionize a high-density target before it hydrodynamically expands. The transport of such electrons within a solid target has been studied using two-dimensional (2D) imaging of electron-induced Kα radiation. However, it is currently limited to no or picosecond scale temporal resolutions. Here, we demonstrate femtosecond time-resolved 2D imaging of fast electron transport in a solid copper foil using the SACLA x-ray free electron laser (XFEL). An unfocused collimated x-ray beam produced transmission images with sub-micron and ∼10 fs resolutions. The XFEL beam, tuned to its photon energy slightly above the Cu K-edge, enabled 2D imaging of transmission changes induced by electron isochoric heating. Time-resolved measurements obtained by varying the time delay between the x-ray probe and the optical laser show that the signature of the electron-heated region expands at ∼25% of the speed of light in a picosecond duration. Time-integrated Cu Kα images support the electron energy and propagation distance observed with the transmission imaging. The x-ray near-edge transmission imaging with a tunable XFEL beam could be broadly applicable for imaging isochorically heated targets by laser-driven relativistic electrons, energetic protons, or an intense x-ray beam.

A flexible proton beam imaging energy spectrometer (PROBIES) for high repetition rate or single-shot high energy density (HED) experiments (invited)

The PROBIES diagnostic is a new, highly flexible, imaging and energy spectrometer designed for laser-accelerated protons. The diagnostic can detect low-mode spatial variations in the proton beam profile while resolving multiple energies on a single detector or more. When a radiochromic film stack is employed for "single-shot mode," the energy resolution of the stack can be greatly increased while reducing the need for large numbers of films; for example, a recently deployed version allowed for 180 unique energy measurements spanning ∼3 to 75 MeV with <0.4 MeV resolution using just 20 films vs 180 for a comparable traditional film and filter stack. When utilized with a scintillator, the diagnostic can be run in high-rep-rate (>Hz rate) mode to recover nine proton energy bins. We also demonstrate a deep learning-based method to analyze data from synthetic PROBIES images with greater than 95% accuracy on sub-millisecond timescales and retrained with experimental data to analyze real-world images on sub-millisecond time-scales with comparable accuracy.

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

2D monochromatic x-ray imaging for beam monitoring of an x-ray free electron laser and a high-power femtosecond laser

In pump-probe experiments with an X-ray Free Electron Laser (XFEL) and a high-power optical laser, spatial overlap of the two beams must be ensured to probe a pumped area with the x-ray beam. A beam monitoring diagnostic is particularly important in short-pulse laser experiments where a tightly focused beam is required to achieve a relativistic laser intensity for generation of energetic particles. Here, we report the demonstration of on-shot beam pointing measurements of an XFEL and a terawatt class femtosecond laser using 2D monochromatic Kα imaging at the Matter in Extreme Conditions end-station of the Linac Coherent Light Source. A thin solid titanium foil was irradiated by a 25-TW laser for fast electron isochoric heating, while a 7.0 keV XFEL beam was used to probe the laser-heated region. Using a spherical crystal imager (SCI), the beam overlap was examined by measuring 4.51 keV Kα x rays produced by laser-accelerated fast electrons and the x-ray beam. Measurements were made for XFEL-only at various focus lens positions, laser-only, and two-beam shots. Successful beam overlapping was observed on ∼58% of all two-beam shots for 10 μm thick samples. It is found that large spatial offsets of laser-induced Kα spots are attributed to imprecise target positioning rather than shot-to-shot laser pointing variations. By applying the Kα measurements to x-ray Thomson scattering measurements, we found an optimum x-ray beam spot size that maximizes scattering signals. Monochromatic x-ray imaging with the SCI could be used as an on-shot beam pointing monitor for XFEL-laser or multiple short-pulse laser experiments.

Time-Resolved Fuel Density Profiles of the Stagnation Phase of Indirect-Drive Inertial Confinement Implosions

The implosion efficiency in inertial confinement fusion depends on the degree of stagnated fuel compression, density uniformity, sphericity, and minimum residual kinetic energy achieved. Compton scattering-mediated 50-200 keV x-ray radiographs of indirect-drive cryogenic implosions at the National Ignition Facility capture the dynamic evolution of the fuel as it goes through peak compression, revealing low-mode 3D nonuniformities and thicker fuel with lower peak density than simulated. By differencing two radiographs taken at different times during the same implosion, we also measure the residual kinetic energy not transferred to the hot spot and quantify its impact on the implosion performance.

The MDM2 ligand Nutlin-3 differentially alters expression of the immune blockade receptors PD-L1 and CD276

BACKGROUND

The links between the p53/MDM2 pathway and the expression of pro-oncogenic immune inhibitory receptors in tumor cells are undefined. In this report, we evaluate whether there is p53 and/or MDM2 dependence in the expression of two key immune receptors, CD276 and PD-L1.

METHODS

Proximity ligation assays were used to quantify protein-protein interactions in situ in response to Nutlin-3. A panel of p53-null melanoma cells was created using CRISPR-Cas9 guide RNA mediated genetic ablation. Flow cytometric analyses were used to assess the impact of TP53 or ATG5 gene ablation, as well as the effects of Nutlin-3 and an ATM inhibitor on cell surface PD-L1 and CD276. Targeted siRNA was used to deplete CD276 to assess changes in cell cycle parameters by flow cytometry. A T-cell proliferation assay was used to assess activity of CD4+ T-cells as a function of ATG5 genotype.

RESULTS

CD276 forms protein-protein interactions with MDM2 in response to Nutlin-3, similar to the known MDM2 interactors p53 and HSP70. Isogenic HCT116 p53-wt/null cancer cells demonstrated that CD276 is induced on the cell surface by Nutlin-3 in a p53-dependent manner. PD-L1 was also unexpectedly induced by Nutlin-3, but PD-L1 does not bind MDM2. The ATM inhibitor KU55993 reduced the levels of PD-L1 under conditions where Nutlin-3 induces PD-L1, indicating that MDM2 and ATM have opposing effects on PD-L1 steady-state levels. PD-L1 is also up-regulated in response to genetic ablation of TP53 in A375 melanoma cell clones under conditions in which CD276 remains unaffected. A549 cells with a deletion in the ATG5 gene up-regulated only PD-L1, further indicating that PD-L1 and CD276 are under distinct genetic control.

CONCLUSION

Genetic inactivation of TP53, or the use of the MDM2 ligand Nutlin-3, alters the expression of the immune blockade receptors PD-L1 and CD276. The biological function of elevated CD276 is to promote altered cell cycle progression in response to Nutlin-3, whilst the major effect of elevated PD-L1 is T-cell suppression. These data indicate that TP53 gene status, ATM and MDM2 influence PD-L1 and CD276 paralogs on the cell surface. These data have implications for the use of drugs that target the p53 pathway as modifiers of immune checkpoint receptor expression.

HO-1 drives autophagy as a mechanism of resistance against HER2-targeted therapies

PURPOSE

Targeted therapies have resulted in major advances in the treatment of HER2-positive breast cancers. Despite this, up to 70% of patients will develop resistance to treatment within 2 years and new strategies for targeting resistant disease are needed.

METHODS

To identify potential resistance mechanisms, we used the mouse MMTV-NIC-PTEN+/- spontaneous model of HER2-positive breast cancer and the pan-HER family kinase inhibitor sapatinib. Vehicle and sapatinib-treated tumors were evaluated by immunohistochemistry and proteomic analysis. In vitro studies were carried out to define the role of heme oxygenase 1 (HO-1) and autophagy in resistance to sapatinib and lapatinib, another pan-HER family kinase inhibitor.

RESULTS

Treatment of tumor-bearing MMTV-NIC-PTEN+/- mice with sapatinib resulted in delayed tumor progression and increased survival. However, tumors eventually progressed on treatment. Proteomic analysis identified proteins associated with cellular iron homeostasis as being upregulated in the sapatinib-treated tumors. This included HO-1 whose overexpression was confirmed by immunohistochemistry. Overexpression of HO-1 in HER2-expressing SKBR3 breast cancer cells resulted in reduced sensitivity to both pan-HER family kinase inhibitors sapatinib and lapatinib. This was associated with increased autophagy in the HO-1 over-expressing cells. Furthermore, increased autophagy was also seen in the sapatinib-treated tumors. Treatment with autophagy inhibitors was able to increase the sensitivity of the HO-1 over-expressing cells to both lapatinib and sapatinib.

CONCLUSION

Together these data indicate a role for HO-1-induced autophagy in resistance to pan-HER family kinase inhibitors.

Generating keV ion distributions for nuclear reactions at near solid-density using intense short-pulse lasers

Our understanding of a large range of astrophysical phenomena depends on a precise knowledge of charged particle nuclear reactions that occur at very low rates, which are difficult to measure under relevant plasma conditions. Here, we describe a method for generating dense plasmas at effective ion temperatures >20 keV, sufficient to induce measurable charged particle nuclear reactions. Our approach uses ultra-intense lasers to drive micron-sized, encapsulated nanofoam targets. Energetic electrons generated in the intense laser interaction pass through the foam, inducing a rapid expansion of the foam ions; this results in a hot, near-solid density plasma. We present the laser and target conditions necessary to achieve these conditions and illustrate the system performance using three-dimensional particle-in-cell simulations, outline potential applications and calculate expected nuclear reaction rates in the D(d,n) and 12C(p,γ) systems assuming CD, or CH aerogel foams.

Monochromatic 2D Kα Emission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

The rapid heating of a thin titanium foil by a high intensity, subpicosecond laser is studied by using a 2D narrow-band x-ray imaging and x-ray spectroscopy. A novel monochromatic imaging diagnostic tuned to 4.51 keV Ti Kα was used to successfully visualize a significantly ionized area (⟨Z⟩>17±1) of the solid density plasma to be within a ∼35  μm diameter spot in the transverse direction and 2  μm in depth. The measurements and a 2D collisional particle-in-cell simulation reveal that, in the fast isochoric heating of solid foil by an intense laser light, such a high ionization state in solid titanium is achieved by thermal diffusion from the hot preplasma in a few picoseconds after the pulse ends. The shift of Kα and formation of a missing Kα cannot be explained with the present atomic physics model. The measured Kα image is reproduced only when a phenomenological model for the Kα shift with a threshold ionization of ⟨Z⟩=17 is included. This work reveals how the ionization state and electron temperature of the isochorically heated nonequilibrium plasma are independently increased.

CCPG1 Is a Non-canonical Autophagy Cargo Receptor Essential for ER-Phagy and Pancreatic ER Proteostasis

Mechanisms of selective autophagy of the ER, known as ER-phagy, require molecular delineation, particularly in vivo. It is unclear how these events control ER proteostasis and cellular health. Here, we identify cell-cycle progression gene 1 (CCPG1), an ER-resident protein with no known physiological role, as a non-canonical cargo receptor that directly binds to core autophagy proteins via an LIR motif to mammalian ATG8 proteins and, independently and via a discrete motif, to FIP200. These interactions facilitate ER-phagy. The CCPG1 gene is inducible by the unfolded protein response and thus directly links ER stress to ER-phagy. In vivo, CCPG1 protects against ER luminal protein aggregation and consequent unfolded protein response hyperactivation and tissue injury of the exocrine pancreas. Thus, via identification of this autophagy protein, we describe an unexpected molecular mechanism of ER-phagy and provide evidence that this may be physiologically relevant in ER luminal proteostasis.

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CCPG1 is an ER stress-inducible ER-phagy cargo receptor in mammals

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CCPG1 binds directly to ATG8 proteins and FIP200 via distinct peptide motifs

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CCPG1 lysosomal degradation and ER-phagy both require these interactions

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CCPG1 maintains normal ER luminal proteostasis in pancreatic acinar cells in vivo

FLCN, a novel autophagy component, interacts with GABARAP and is regulated by ULK1 phosphorylation

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant condition caused by mutations in the FLCN gene and characterized by benign hair follicle tumors, pneumothorax, and renal cancer. Folliculin (FLCN), the protein product of the FLCN gene, is a poorly characterized tumor suppressor protein, currently linked to multiple cellular pathways. Autophagy maintains cellular homeostasis by removing damaged organelles and macromolecules. Although the autophagy kinase ULK1 drives autophagy, the underlying mechanisms are still being unraveled and few ULK1 substrates have been identified to date. Here, we identify that loss of FLCN moderately impairs basal autophagic flux, while re-expression of FLCN rescues autophagy. We reveal that the FLCN complex is regulated by ULK1 and elucidate 3 novel phosphorylation sites (Ser406, Ser537, and Ser542) within FLCN, which are induced by ULK1 overexpression. In addition, our findings demonstrate that FLCN interacts with a second integral component of the autophagy machinery, GABA(A) receptor-associated protein (GABARAP). The FLCN-GABARAP association is modulated by the presence of either folliculin-interacting protein (FNIP)-1 or FNIP2 and further regulated by ULK1. As observed by elevation of GABARAP, sequestome 1 (SQSTM1) and microtubule-associated protein 1 light chain 3 (MAP1LC3B) in chromophobe and clear cell tumors from a BHD patient, we found that autophagy is impaired in BHD-associated renal tumors. Consequently, this work reveals a novel facet of autophagy regulation by ULK1 and substantially contributes to our understanding of FLCN function by linking it directly to autophagy through GABARAP and ULK1.

Deflection of MeV electrons by self-generated magnetic fields in intense laser-solid interactions

We show that the interaction of relativistic-intensity, picosecond laser pulses with solid targets is affected by the reflected light through the strong currents and 10(4)  T magnetic fields it produces. Three-dimensional particle-in-cell simulations, with the axisymmetry broken by a small angle of incidence, show that these magnetic fields deflect the laser-accelerated electrons away from the incident laser axis. This directly impacts the interpretation of electron divergence and directionality in applications such as laser-driven ion acceleration or fast-ignition inertial fusion.

A yeast tRNA mutant that causes pseudohyphal growth exhibits reduced rates of CAG codon translation

In Saccharomyces cerevisiae, the SUP70 gene encodes the CAG-decoding tRNA(Gln)(CUG). A mutant allele, sup70-65, induces pseudohyphal growth on rich medium, an inappropriate nitrogen starvation response. This mutant tRNA is also a UAG nonsense suppressor via first base wobble. To investigate the basis of the pseudohyphal phenotype, 10 novel sup70 UAG suppressor alleles were identified, defining positions in the tRNA(Gln)(CUG) anticodon stem that restrict first base wobble. However, none conferred pseudohyphal growth, showing altered CUG anticodon presentation cannot itself induce pseudohyphal growth. Northern blot analysis revealed the sup70-65 tRNA(Gln)(CUG) is unstable, inefficiently charged, and 80% reduced in its effective concentration. A stochastic model simulation of translation predicted compromised expression of CAG-rich ORFs in the tRNA(Gln)(CUG)-depleted sup70-65 mutant. This prediction was validated by demonstrating that luciferase expression in the mutant was 60% reduced by introducing multiple tandem CAG (but not CAA) codons into this ORF. In addition, the sup70-65 pseudohyphal phenotype was partly complemented by overexpressing CAA-decoding tRNA(Gln)(UUG), an inefficient wobble-decoder of CAG. We thus show that introducing codons decoded by a rare tRNA near the 5' end of an ORF can reduce eukaryote translational expression, and that the mutant tRNA(CUG)(Gln) constitutive pseudohyphal differentiation phenotype correlates strongly with reduced CAG decoding efficiency.

Interaction physics of multipicosecond Petawatt laser pulses with overdense plasma

We study the interaction of intense petawatt laser pulses with overdense plasma over several picoseconds, using two- and three-dimensional kinetic particle simulations. Sustained irradiation with non-diffraction-limited pulses at relativistic intensities yields conditions that differ qualitatively from what is experimentally available today. Nonlinear saturation of laser-driven density perturbations at the target surface causes recurrent emissions of plasma, which stabilize the surface and keep absorption continuously high. This dynamics leads to the acceleration of three distinct groups of electrons up to energies many times the laser ponderomotive potential. We discuss their energy distribution for applications like the fast-ignition approach to inertial confinement fusion.

Dynamics of relativistic laser-plasma interaction on solid targets

A novel time-resolved diagnostic is used to record the critical surface motion during picosecond-scale relativistic laser interaction with a solid target. Single-shot measurements of the specular light show a redshift decreasing with time during the interaction, corresponding to a slowing-down of the hole boring process into overdense plasma. On-shot full characterization of the laser pulse enables simulations of the experiment without any free parameters. Two-dimensional particle-in-cell simulations yield redshifts that agree with the data, and support a simple explanation of the slowing-down of the critical surface based on momentum conservation between ions and reflected laser light.

Hot electron temperature and coupling efficiency scaling with prepulse for cone-guided fast ignition

The effect of increasing prepulse energy levels on the energy spectrum and coupling into forward-going electrons is evaluated in a cone-guided fast-ignition relevant geometry using cone-wire targets irradiated with a high intensity (10(20) W/cm(2)) laser pulse. Hot electron temperature and flux are inferred from Kα images and yields using hybrid particle-in-cell simulations. A two-temperature distribution of hot electrons was required to fit the full profile, with the ratio of energy in a higher energy (MeV) component increasing with a larger prepulse. As prepulse energies were increased from 8 mJ to 1 J, overall coupling from laser to all hot electrons entering the wire was found to fall from 8.4% to 2.5% while coupling into only the 1-3 MeV electrons dropped from 0.57% to 0.03%.

Limitation on prepulse level for cone-guided fast-ignition inertial confinement fusion

The viability of fast-ignition (FI) inertial confinement fusion hinges on the efficient transfer of laser energy to the compressed fuel via multi-MeV electrons. Preformed plasma due to the laser prepulse strongly influences ultraintense laser plasma interactions and hot electron generation in the hollow cone of an FI target. We induced a prepulse and consequent preplasma in copper cone targets and measured the energy deposition zone of the main pulse by imaging the emitted K_{alpha} radiation. Simulation of the radiation hydrodynamics of the preplasma and particle in cell modeling of the main pulse interaction agree well with the measured deposition zones and provide an insight into the energy deposition mechanism and electron distribution. It was demonstrated that a under these conditions a 100 mJ prepulse eliminates the forward going component of approximately 2-4 MeV electrons.

Hot-electron energy coupling in ultraintense laser-matter interaction

We investigate the hydrodynamic response of plasma gradients during the interaction with ultraintense energetic laser pulses using kinetic particle simulations. Energetic laser pulses are capable of compressing preformed plasma gradients over short times, while accelerating low-density plasma backward. As light is absorbed on a steepened interface, hot-electron temperature and coupling efficiency drop below the ponderomotive scaling and we are left with an absorption mechanism that strongly relies on the electrostatic potential caused by low-density preformed plasma. We describe this process, discuss properties of the resulting electron spectra and identify the parameter regime where strong compression occurs. Finally, we discuss implications for fast ignition and other applications.

Power scaling of Nd:YVO4 and Nd:GdVO4 disk lasers using synthetic diamond as a heat spreader

A newly developed low-birefringence synthetic diamond is shown to be an effective intracavity heat spreader in Nd:YVO4 and Nd:GdVO4 disk lasers. A cw output power of 25.7 W from only one double pass of the pump is reported. The diamond heat spreader is shown to increase the pump power density at which fracture occurs.

Diagnostics for fast ignition science (invited)

The ignition concept for electron fast ignition inertial confinement fusion requires sufficient energy be transferred from an approximately 20 ps laser pulse to the compressed fuel via approximately MeV electrons. We have assembled a suite of diagnostics to characterize such transfer, simultaneously fielding absolutely calibrated extreme ultraviolet multilayer imagers at 68 and 256 eV; spherically bent crystal imagers at 4.5 and 8 keV; multi-keV crystal spectrometers; MeV x-ray bremmstrahlung, electron and proton spectrometers (along the same line of sight), and a picosecond optical probe interferometer. These diagnostics allow careful measurement of energy transport and deposition during and following the laser-plasma interactions at extremely high intensities in both planar and conical targets. Together with accurate on-shot laser focal spot and prepulse characterization, these measurements are yielding new insights into energy coupling and are providing critical data for validating numerical particle-in-cell (PIC) and hybrid PIC simulation codes in an area crucial for fast ignition and other applications. Novel aspects of these diagnostics and how they are combined to extract quantitative data on ultrahigh intensity laser-plasma interactions are discussed.

Hot-electron energy coupling in ultraintense laser-matter interaction

We investigate the hydrodynamic response of plasma gradients during the interaction with ultraintense energetic laser pulses, using kinetic particle simulations. Energetic laser pulses are capable of compressing preformed plasma gradients over short times while accelerating low-density plasma backwards. As light is absorbed on a steepened interface, hot-electron temperature and coupling efficiency drop below the ponderomotive scaling, and we are left with a new absorption mechanism that strongly relies on the electrostatic potential caused by low-density preformed plasma. We describe this process, explain electron spectra, and identify the parameter regime where strong compression occurs. Finally, we discuss the implications for fast ignition and other applications.

Laser heating of solid matter by light-pressure-driven shocks at ultrarelativistic intensities

The heating of solid targets irradiated by 5 x 10(20) W cm(-2), 0.8 ps, 1.05 microm wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo, and V. A surface layer is heated to approximately 5 keV with an axial temperature gradient of 0.6 microm scale length. Images of Ni Ly(alpha) show the hot region has <or=25 microm diameter. These data are consistent with collisional particle-in-cell simulations using preformed plasma density profiles from hydrodynamic modeling which show that the >100 G bar light pressure compresses the preformed plasma and drives a shock into the solid, heating a thin layer.

Collisional relaxation of superthermal electrons generated by relativistic laser pulses in dense plasma

Energy relaxation of the hot electron population generated by relativistic laser pulses in overdense plasma is analyzed for densities ranging from below to 1000 times solid density. It is predicted that longitudinal beam-plasma instabilities, which dominate energy transfer between hot electrons and plasma at lower densities, are suppressed by collisions beyond solid density. The respective roles of collisional energy transfer modes, i.e., direct collisions, diffusion, and resistive return current heating, are identified with respect to plasma density. The transition between the kinetic and the collisional regimes and scalings of collisional process are demonstrated by a fully integrated one-dimensional collisional particle simulation.

Phylogenetic analysis of the precore/core gene of hepatitis B virus genotypes E and A in West Africa: new subtypes, mixed infections and recombinations

One hundred and twenty-two new hepatitis B virus (HBV) preC/C sequences and three complete genomes from three major countries in West Africa were analysed. The majority of sequences were of genotype E and the only other genotype found was genotype A. Although for genotype E sequences, the genetic diversity of the preC/C gene was about two to three times higher than that of the preS/S gene, it was still considerably lower than that for genotype A sequences. The HBV/E preC/C gene was related most closely to subgenotype D1 and D2 sequences. Evidence of recombination was found in two strains that were of genotype A in the preS/S gene and of genotype E in the preC/C gene. The genotype A strains from Cameroon, Mali and Nigeria could be divided phylogenetically into three subtypes, A3 and two new subtypes, tentatively designated A4 and A5. Each subtype presented a genetic diversity of 2.19-3.85 % and intersubtype distances of 4.47-5.97 %. Interestingly, one sample from Nigeria showed evidence of a triple recombination of genotypes E/D and A, separated by a genotype G-specific insert of 36 bp. Of 110 patients, 19 (17.3 %) showed a coinfection of genotypes A and E, mostly in human immunodeficiency virus-positive children from Cameroon. Thus, in Cameroon, where both genotypes coexist, 37 % of all individuals tested had mixed infections. The low genetic variability in the preC/C gene of genotype E supports our previous speculation about a relatively short evolutionary history of this genotype, in contrast to the subtype-rich African genotype A strains.

Effect of bone meal (calcium phosphate) amendments on metal release from contaminated soils--a leaching column study

Metal-contaminated soil may be remediated in situ by the formation of highly insoluble metal phosphates if an appropriate phosphorus (P) source can be found. Leaching column experiments have been carried out to assess the suitability of bone meal as such a source. Bone meal additions reduced metal release from a contaminated soil, increased soil and leachate pH and decreased soil leachate toxicity. Minimal P leaching occurred from the soil. The data are consistent with a proton consuming bone meal (calcium phosphate) dissolution reaction followed by the formation of metal phosphates. Although, no metal phosphates were observed to form using X-ray diffraction of scanning electron microscopy this could be due to their low concentration. Relatively low (1:50 bone meal:soil) concentrations of fine (90-500 microns) bone meal would appear to be an effective treatment for metal-contaminated soils.

Compact and efficient Nd:YVO 4 laser that generates a tunable single-frequency green output

We demonstrate 250 mW of single-frequency 532-nm output from a simple intracavity-doubled Nd:YVO(4) laser, pumped with 1.2 W from a fiber-coupled diode laser. The laser can be frequency chirped smoothly over approximately 17 GHz while maintaining a single-frequency green output of greater than 200 mW. A short Fabry-Perot cavity is used, and single-frequency operation is enforced by means of a birefringent filter that utilizes the birefringence of both the KTP doubling crystal and the Nd:YVO(4) laser crystal with polarization-dependent loss from a glass Brewster plate combined with polarization-dependent gain from the laser crystal.

Changes in the proportions of peripheral blood lymphocytes in patients with worn implants

We compared the peripheral blood and periprosthetic tissues of 53 patients at revision arthroplasty with those of 30 patients at primary arthroplasty to determine whether there is a systemic difference in lymphocytes in patients with worn hip implants. The absolute number and relative proportion of lymphocytes bearing CD2, CD3, CD4, CD8, CD16, CD19, HLA-DR, kappa and lambda antigens were compared with the levels of IL-1beta, IL-6 and PGE2 in the pseudosynovial membrane as well as with a semiquantitative estimate of metal and polyethylene particles, necrosis and chronic inflammation and the total concentration of metals within the periprosthetic tissues. There was a significant increase in the relative proportion of CD2-positive T-cells and CD16-positive natural killer cells in the peripheral blood at revision arthroplasty compared with primary arthroplasty and an increased proportion of CD8-positive T-cells and a decreased ratio of CD4 to CD8 (helper inducer/suppressor cytotoxic cells). Three control patients, who went on to have revision surgery, had values at primary arthroplasty which were similar to those of patients at the time of revision surgery. These differences did not correlate with the local concentration of metal, plastic or cement or inflammatory response or the type of prosthesis. An inverse correlation was noted between the necrosis in the periprosthetic tissue and both the local production of IL-6 and the absolute numbers of T-cells in peripheral blood. We conclude that there may be several cell-mediated systemic immune responses to aseptic loosening, at least one of which may be directly related to events in the periprosthetic tissues. We cannot exclude the possibility that the changes in the proportion of CD8-positive cells reflected a predisposition, rather than a reaction, to loosening of the implant.

Microchip laser-pumped continuous-wave doubly resonant optical parametric oscillator

We report what we believe to be the first use of a multilongitudinal-mode frequency-doubled microchip laser to pump a doubly resonant optical parametric oscillator (OPO). This compact OPO is based on potassium titanyl phosphate (KTP) and operates with a low pump power threshold of 35 mW. The OPO output consists of a single pair of signal and idler modes even though it is pumped with a multilongitudinal-mode pump laser. We achieved smooth tuning (1.7 GHz) of the output frequencies by temperature tuning of the pump laser.

Self-Q-switched Nd:YVO4 microchip lasers

We have observed giant pulses from cw pumped, monolithic Nd:YVO(4) microchip lasers, several hundred times the cw level, with pulse lengths less than 2 ns, which cannot be accounted for by conventional gain switching. These pulses occur as the second longitudinal mode starts to oscillate and can be described by the inclusion of gain-related effects in the formation of a stable cavity.

Microchip Nd:vanadate lasers at 1342 and 671nm

As much as 105 mW of single-frequency output at 1342 nm was obtained from a diode-laser-pumped Nd:YVO(4) microchip laser. An intracavity frequency-doubled device generated 10 mW of single-frequency red radiation.

Tumors around implants

In 1989, A. G. Apley recommended cautious surveillance of malignant tumors that developed in association with orthopaedic implants. This retrospective review of the Bristol Bone Tumour Register between 1980 and 1992 reports on 240 malignant soft tissue sarcomas. Eighteen developed in the thigh region of patients more than 50 years old, and 4 of these developed in the soft tissues around a hip arthroplasty.

Widespread dissemination of metal debris from implants

In a post-mortem study, we compared subjects with metal implants with and without visible wear with an age-matched control group to determine the extent and effects of dissemination of wear debris. In subjects with stainless-steel and cobalt-chrome prostheses metal was found in local and distant lymph nodes, bone marrow, liver and spleen. The levels were highest in subjects with loose, worn joint prostheses and the main source of the debris was the matt coating. Metal levels were also raised in subjects with implants without visible wear and, to a less extent, in those with dynamic hip screws. Necrosis of lymph nodes was seen in those cases with the most wear, and potential damage to more distant organs such as the bone marrow, liver and spleen in the long term cannot be discounted. The consequences for the immune system and the role of metal dissemination in the possible induction of neoplasia are discussed.

Widespread dissemination of metal debris from implants

In a post-mortem study, we compared subjects with metal implants with and without visible wear with an age-matched control group to determine the extent and effects of dissemination of wear debris. In subjects with stainless-steel and cobalt-chrome prostheses metal was found in local and distant lymph nodes, bone marrow, liver and spleen. The levels were highest in subjects with loose, worn joint prostheses and the main source of the debris was the matt coating. Metal levels were also raised in subjects with implants without visible wear and, to a less extent, in those with dynamic hip screws. Necrosis of lymph nodes was seen in those cases with the most wear, and potential damage to more distant organs such as the bone marrow, liver and spleen in the long term cannot be discounted. The consequences for the immune system and the role of metal dissemination in the possible induction of neoplasia are discussed.

Multiple benign stromal cell tumours of the small bowel

A rare case of multiple small intestinal stromal cell tumours is described in a 79 year old woman who presented with melaena and anaemia. At surgery, about 40 lesions were noted on the serosal surface of the small intestine, the largest of these tumours being located in the mid-jejunum. This lesion showed central necrosis and haemorrhage with a sinus opening into the jejunal lumen. Histological examination of this jejunal tumour showed epithelioid and spindle shaped cells. A smaller biopsied tumour was a pure spindle cell lesion. Both lesions fitted the criteria for benign stromal cell tumours. Although skenoid fibres were identified, the immunophenotype was characteristically heterogeneous. Multiple benign small intestinal tumours can raise the spectre of metastases when seen at surgery, although their presence in this case does not seem to indicate this.

Dual effects of pyrazofurin and 3-deazauridine upon pyrimidine and purine biosynthesis in mouse L1210 leukemia

Pyrazofurin (NSC 143095) as the monophosphate derivative is a potent inhibitor of orotidine 5'-monophosphate (OMP) decarboxylase of the pyrimidine pathway and has been proposed to inhibit 5-aminoimidazole-4-carboxamide ribotide (AICAR) transformylase (EC 2.1.2.3) of the purine pathway (J. F. Worzalla, and M. J. Sweeney, Pyrazofurin inhibition of purine biosynthesis via 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranosyl 5'-monophosphate formyltransferase. Cancer Res., 40: 1482-1485, 1980). Measurement of levels of pyrimidine and purine intermediates in cultured mouse L1210 leukemia cells has shown that 25 microM pyrazofurin induces an 8-fold accumulation of OMP and large accumulations of intermediates proximal to the blockade with abrupt decreases in uridine and cytidine nucleotides. Considerable increases in the cellular concentrations of N-succino-AICAR (SAICAR), AICAR, 5-formamidoimidazole-4-carboxamide ribotide (FAICAR), IMP, XMP, and GMP at later times indicate that AICAR transformylase is not significantly inhibited in cultured cells; rather the purine pathway and the GMP branch are stimulated. However, addition of 25 microM 3-deazauridine (NSC 126849) to leukemia cells did result in inhibition of AICAR transformylase: AICAR and SAICAR accumulated, IMP disappeared and there was a large accumulation of guanosine nucleotides. Blockade of pyrimidine biosynthesis by derivatives of pyrazofurin or 3-deazauridine spares 5-phosphoribosyl-1-pyrophosphate and L-glutamine, elevated concentrations of which may stimulate initial reactions of purine biosynthesis and the reaction XMP----GMP.

Effects of acivicin and dichloroallyl lawsone upon pyrimidine biosynthesis in mouse L1210 leukemia cells

Acivicin (NSC 163501) and dichloroallyl lawsone (NSC 126771) are potent inhibitors of nucleotide biosynthesis with consequent anti-cancer activity against certain experimental tumors. To determine in detail the metabolic events induced by each inhibitor, we have devised a new two-dimensional chromatographic procedure for measurement of the concentrations of all pyrimidine intermediates and some purine nucleotides from 100 microliter of an extract of cells grown in the presence of [14C]bicarbonate. Addition of acivicin (25 microM) to mouse L1210 leukemia cells causes severe depletion in the cellular levels of CTP and GTP, accumulation of uridine nucleotides, and abrupt but transient increases in the concentrations of the early intermediates of both the pyrimidine and purine pathways. Addition of dichloroallyl lawsone (25 microM) results in a rapid depletion of uridine and cytidine nucleotides; carbamyl aspartate and dihydroorotate accumulate to high levels in an equilibrium ratio of 20.5:1, and orotate, orotidine, and UMP increase transiently before decreasing to levels approaching their original steady states. The predominant inhibitory effects of acivicin are upon the reactions UTP----CTP and XMP----GMP, but there is also an initial transient activation of both the pyrimidine and purine pathways by acivicin. The data obtained with dichloroallyl lawsone are consistent with inhibition of the conversion of UMP----UDP initially followed by potent inhibition of dihydroorotate----orotate.